The AM Forum

Question.  George has both 230 and 115 volt transformers.  The Gates iron is 230 primary and will provide 1500 DC to the 4-125 or 250 final.  Everything else is 115.  I mentioned early on that I would run 240 to the cabinet and divide it.

After looking at the current-flow possibles in the mains I found balance between both halves of the mains was important.  I plan on plugging into the outlet that leads to our dryer about 10 feet away.  I may tap into that outlet and run 220 to the shack area.  We're talking less than 10 feet so I can keep the rack cord shorter.

Only the RF plate supply will be 220.  RF screen, bias & fils plus the modulator are all 115 iron.  The modulator has a Thordarson plate iron that will give me 1250DC at .3A.  We're looking at 100 watts of audio at a minimum.  The fils for PP 811As are also 115.  All of these have to be balanced on each side of the incoming 220 I assume?  The tap to the dryer is on a solid and little used breaker. 

How critical is it to divide loads from a 220V main into a 300 watt input (max) AM amp and modulator when only the PA plate iron is 220? 

George,

You configuration for good design practice requires you to have a 4 wire feed from your service entrance panel.  L1 which we will define as one side of your 240 feed.  L2 which is the other end of your 240V feed.  A neutral and finally a safety ground.  You need that center tap provided by the neutral to assure that you have 120V on each side of that neutral to power your lower voltage 120V primary transformers.  I would distribute the 120V primaries on each side of neutral although that is not absolutely necessary.  Your 240V which is obtained from L1 to L2 will power your larger 240V primary transformer.   Size your breaker back in your service panel for the load current and make sure the wire gauge is adequate for the current level your protecting with the chosen breaker. 

The safety ground should not be carrying any current. 

Hope that helps.

Joe, W3GMS   

If you have stout wire, balancing won't matter as much. Making the cable as short as possible and making the neutral 2x larger than necessary helps greatly with balance.

I have the same unbalance thing with a rig here where the RF is on one side of the 240V and the modulator is on the other side. Hots are 10 gauge, neutral is two 10 gauges in parallel. With 2000W DC to one side and the other 'off', as would be for CW, it's less than 2V difference in the balance. The safety ground is also a #10. I happened to find a 30FT 'scrap' of 5-conductor cable 8-). would hate to buy that today.

I would follow Joe's advice.  If your dryer line outlet does not have a neutral, you will have a hard time balancing 120v loads across a 240 volt feed.  You need a neutral.

Fred

Looking at ur picture and scratching my head leaves me with one design question.

Why are you using plug in replacement rectifiers instead of something more compact like microwave oven diode blocks. (K2AW rectifier diodes, etc)? ? ?

It would give you more room to finagel things around on the chassis, and they are pretty cheap and reasonable. They are also compact and easy to install.
Unless I am going for a "period correct" look, I use them for everything high voltage.

Also, be careful using the dryer feed or dryer socket. Many (most) of them nowadays are wired with 2 hots and a safety ground only. (no neutral)
An easy way to tell is simply to look at the socket. If it has 3 prongs, it has NO neutral, if it has 4, it does.

Basically, If you plan to have any 120 volt loads - you must have a neutral. The NEC does not allow any current flowing through the green "ground" or grounding conductor.

As Slab says - many dryers are not supplied with a neutral and have a 3 wire cord. Years ago - the NEC allowed appliances to use the "green" ground to have a few mA of current to run a timer or clock on ranges and dryers. That was stopped and any 120 volt device - no matter how small the current needs a neutral or "grounded conductor"

The neutral may be "reduced" if the load on the 240/120 volt branch circuit has mostly 240 volt load - typically by no more than 50%.

Size your wire for the load using 60 degree C tables for loads under 100 amperes. If the load is "continuous" (operates for 2 hours or more) size the wire for 125% of the load. Size the breaker to the wire size. The breaker does not protect the load - it protects the wire.

A 30 amp breaker will pass 30 amps forever and 60 amps for minutes.



Pat
N4LTA

The NEC is in business to protect the permanently stupid, keep them employed writing new regs, employ more union electricians and generally cost the consumer money for no added benefit.

The 3 wire 240V with 2 hots and a ground has worked fine for decades in dryers, ovens and similar....no body has been fried by having the 120V devices hung from one hot to ground.

Even several ham products did it including Alpha, Henry, and Johnson.

These days its still OK to hang the 120V fans, etc across one half of a dual 120V winding that is in series for 240V, nothing goes to ground. No overprice wire, conector or outlets required.

In the case where the 240V transformer is only a single winding I suggest seperate 120 and 240V outlets unless you want to rip the house apart to run a 4 wire feed, etc. just to keep your insurance in effect and the building inspector employed.

My HB 2M 1500W amp is still wired the old way for the almost 30 years its been there since it has only a single 240V winding. The feed from the panel is 10-3 and the cord is 12-3. There is no voltage difference between the combined ground/neutral and the copper water pipes overhead which are bonded together there and back at the panel where they are tied to the the ground rods.

If anybody asks its a 1500W heater ::)

I am probably one of those idiots that keep themselves employed by the NEC.

Just a little side item - though - the year before the GFI (many say stupidly put into law) was put into law -over 2500 people were killed with 120 volt to ground electricutions.

Last year the number was less than 50

In 20 years time that may add up to as many as 40,000 people that did not die.

If you accidently open that harmless oven ground -feeling safe  because a ground wire has no voltage and can't hurt you - you have 120 volts trying to push that 1/4 amp through your body - likely you won't be killed but if you are under a sink or crammed in a close space - who knows?

The NEC has reasons for every rule. Grounding conductor current is not allowed and in many cases is dangerous. I have witnessed too many injuries and deaths in my career. It's the stuff that seems safe that usually hurts people.
I had a friend from my hometown that went to electrical engineering school at NCSU (same as me) and was a couple of years older. He was killed one summer with a metal Black and Decker drill working under the house when the drill grounded. I am sure that the ground prong was not connected.

Pat
N4LTA

Sometimes the pendulum swings from extreme danger to extreme safety....

I have a Signal 230V/115V Auto transformer here that I'd send George if it were not so dang heavy. Must be good for 15 amps or more. This way with a three wire 230V system (H-H-G) you can make a Neutral in the rack, and any draw from the power line is all 230V with no ground current even though there are 115V loads in the rack referenced to the center tap neutral. Does NEC allow for this option?

I grew up in an old 2 wire 110v system house. I recall my dad straddling two shelves over the basement stairs, house pitch black until the Zippo lighter is lit then looking for the blown screw in fuse. Once found, the pack of spares was always depleted. Then I'd hear, "anyone have a penny"?  ;D

We had a dishwasher in the kitchen, the kind that sat next to the sink, and attached to the sink faucet. The dishwasher had a 3 prong cord in a 2 prong house, so the ground was defeated. Then one day the dishwasher was HOT! Touch the faucet and the dishwasher and it would knock you on your butt. I took a 100 watt lamp and affixed wires to a socket, and put one wire on the dishwasher and one on the faucet. It went full brightness! We used it that way for years!! We knew not to touch it.

These days if someone licks a 9v battery they call a lawyer....

Jim
WD5JKO

Yep - That would be perfect - better than a 4 wire feed because the transformer would limit the current.

I grew up with the same system and my "experimenting" sent my father to the service station or curb market late at night looking for a fuse many times.

Pat
N4LTA

In the case of a ham transmitter there is usually an abundance of ground connections and using a common safety ground and neutral probably isn't such a big deal.  I have been using 3 prong dryer connections for 30 years without issue and have no desire to re do the wiring in my station to correct this.  However, if I was starting with a new installation, I would use 4 wire connection as suggested above.

More of a danger is old transmitters that use fuses on both the hot and neutral side of a 115V primary circuit.  My Collins 30K's do this and sure enough the fuse in the neutral side blew.  Sure enough, I got bit brushing up against something while changing the fuse.  This I need to fix.

We are talking about a ham install by someone with some smarts, so  trying to spin it doesnt fly Pat.

Most of the morons eliminated from the gene pool prior to GFCI likely had their radio, curling iron, razor, etc fall in the tub or pool with them. Even no coders and CBers are smarter than that.....I think.

Many modern tools and appliances have 2 wire cords

NEC wont even let you enjoy a good tingle these days by limiting line bypass caps to values that are useless for the purpose. Once the nanny state produces rules that protect down to the lowest IQ across the board what will they come up with next? And we will also have a population of breeding morons worse than you can believe.

Not trying to spin anything Carl.  Not a thing wrong with a 2 wire cord on a double insulated tool. There is no grounding conductor and no current flowing in it.

I was responding to your review of the NEC:

"The NEC is in business to protect the permanently stupid, keep them employed writing new regs, employ more union electricians and generally cost the consumer money for no added benefit."


We don't agree. I'd bet one hell of a lot of hams don't have a clear understanding of the NEC and the whole idea behind the single point grounding system. Many times have I seen the neutral switched on home made equipment. The AC ground and the antenna ground get confused often. Electrical grounding is not something only idiots don't understand.


I have recently been involved in a very nasty problem with grounding conductor current  - where the grounding conductor was used by a manufacturer of a large piece of equipment as a neutral - 50 amps worth - and they didn't even know this was not allowed.  They stated that a neutral was not required.

The ground was bonded to the water pipe system and the guy removing the valve standing in water had no idea. Imagine how it was holding a 20 pound brass valve with water leaking all over him when the current through the valve was interrupted by his wet self. That's what usually kills people - when you have no ide there is a danger - this guy was not killed thankfully.

Grounds (grounding conductor as defined by the NEC) should not carry current -  That is what the neutral (grounded conductor as defined by the NEC) is for. 

We  agree to disagree - but when someone gets killed  - I don't want to be on your side.
 

Pat
N4LTA

  I once went to change my underwater pool light. The thing was hard wired from a GFCI outlet. So I turned off the breaker, turned off the switch, popped the cover and measured with a DVM to make sure the outlet was dead. So there I was, bare chest wet laying on the concrete with my arms underwater down two feet. When I removed the last screw from the light bezel and pulled the light out of the recessed hole, I was instantly nailed. It was only a few volts, but quite a surprise nevertheless.

 Turns out that the Neutral wire up the power pole was broken loose, so my house was fed 220V with no centertap. The only thing trying to keep things centered was the pool light fixture! If the XYL had turned on something big like the garbage disposal while I removed the light, then I probably wouldn't have survived.

  So the NEC at my house was followed, and I took precautions. I could have been killed just the same. A loose or slippery Ground/Neutral from the power feed connection is very dangerous.

  I guess I'm just a DA. ???

Jim
WD5JKO

Safety aside. Save a little copper, make it up in time chasing hummmm.

Those little voltage drops across neutrals tied to ground become large when audio gear is involved.

First of all, who is George?

This thing with having to have 4 wire service to ham gear is new to me.  I run a Ten Tec Centurion amp, built about 12 years ago and it runs off two hots and a ground.  There is (or was in my case) a 120 v. fan inside it that runs off one end of the plate iron primary and its center tap. 

I've had a licensed electrician come in a few times over the years to run 240 v. circuits because among other things, I stink at bending conduit, and he always ran two hots and a ground.  I have a gas dryer and stove so that may be why the four wire service is foreign to me. 

If I were uncomfortable with running a combination of 240 and 120 v. loads in a cabinet, I'd just put them on separate circuits i.e. service lines, 240 and ground for the plate supply and 120 hot, neutral and ground for the rest of the rig. 

I dimly recall a dispute on some reflector about not having a neutral return for a RF amplifier that ran off two hots and a ground and it ultimately boiled down to a misinterpretation of the NEC as it applied to out-buildings and sub-panels.  Running a 120 v. load across 1/2 of the plate transformer primary was deemed okay.  It might be interesting to find out if Ten Tec still sells the Centurion amp with a three wire cord--I doubt they'd make and sell it that way if it would get them into trouble.

rob 

We are talking about running both 120 and 240 volt loads on a single 240 volt circuit with no neutral.

Using the green grounding conductor as the return for 120 volt current


Pat
N4LTA

George is his transmitter.

I just went through this fiasco a couple years back when wiring up the big transmitter and a Johnson Tbolt.  The T bolt does exactly what George will do.  It runs the plate off 220 but the LV and fils off 120 volt.  That T bolt has a 3 wire cord.  Two hots and a neutral. No ground. I ended up running the a 4 wire 60 amp 240 volt outlet in the room and running plug that has a four wire and the case of the T bolt to the ground pin.

Here in AZ we have no ground at the house. Thats right, no ground.  No ground at the panel and no ground rods at the panel.  Shocked(pun) I called the power company to make sure this is right.  The man came right out, He said there are no grounds as they do not work in sandy soil and your house uses neutral to the shared power transformer outside at the street.  I said I felt like adding a ground rod and ground buss anyways and he said "My house has one" as he walked away.  We put the ground system in next day. Its also gets wet from sprinklers and seems to have conductivity.

The worst possible case was discovered here. Shared neutral.  Whats shared neutral?  That means that all five homes that run off that Power transformer out in the street SHARE a neutral.  Get RF on that line from your shack and you now sent that RF blasting into the neigbors house. 

Jim. your story scared me.  I bet people have died in your exact situation with the pool.
C

In residential service the white wire is neutral and the bare wire is ground.

Now, look at the service panel and tell me there's a difference when you use 4 wire over 3 wire.

I'm with you Carl. Most regulatory agencies (NEC, IEC, UL, CSA) exist now only to justify their existance. Just look at the 61000-4-2 indirect discharge ESD testing.  ::)

OK - I'll tell you there is a big difference

You obviously don't understand the basic concept of AC grounding or the difference would be apparent.

This type of misunderstanding is what causes many grounding problems which can be dangerous and cause transient problems and problems with communication system, as well as safety problems.

The grounding conductor for all NEC power systems is either green in color or bare - usually green. The power company does not supply a ground - they supply a grounded conductor (often called a neutral).
The grounded conductor is bonded at one and only one place - at the service overcurrent device and where the ground system is tied into the system (the grounding electrode).

The grounded conductor (neutral) NEVER is connected to ground downstream. The neutral is a current carrying conductor and so it has voltage drop. The green ground or grounding conductor never carries current except under fault conditions - that is what it is for - to supply a path to trip the overcurrent device. So the neutral condutor is at a different voltage than the grounding conductor. They are not the same and treating them the same causes problems.

I don't really care at all how you wire up your power systems, but the NEC is one of the most important codes for safety that exists. Without it, the safe wiring of power systems would not exist. It is neither brief or simple in concept. I have spent 37 years working with it and am a registered PE in 5 states, and I still learn about it on a regular basis.

I often see the results of ignorance of the NEC and ignorance of proper wiring methods and most of the time it comes from "know it alls" that don't know very much - not ignorant idiots and morons - who for the most part are scared to death of electricity.

Do it anyway you want - there are many ways to make things work - or as a braintrust on here once said "working always beats science". But when the insurance company tells you YOYO ..........

Pat
N4LTA

Around here, the code requires that the neutral be "bonded" to the ground buss only at the main panel. But any sub panels the neutral does not get bonded. And that there can only be one ground point per house. Trying to achive an "RF Ground" like this can be a challenging job at best depending on how long the run is, not to mention the "ground loop" issue.  Also all grounds have to be tied together at one central point. This can be a real P.I.T.A. ! ! !  

to me it seems that the safety grounds on anything coming off of a sub panel now have a longer / higher resistance path to ground.

My house is grounded per NEC, but............. I used to have nasty "RF in the shack" issues. I have since put a 8' ground rod with #2 wire on my tower for lightning protection, and I have drilled a hole in the floor of the basement radio room and driven another 8' ground rod into the virgin soil below the floor. It ties into the back of ALL of my gear with very short copper braid or strapping. I have since totally eliminated any and all of the "RF in the shack" issues, tingles when you touch something, etc. But those grounds do not conform to NEC because they are not bonded to the rest of the house's safety grounds and or neutral bus. They do however get it done when it comes to RF! ! ! !

Clark,
        No system ground at all? ? ? ? ? ? Geeze, the electrical inspectors around here would have organisms! I can see the point with very low soil conductivity,
but I still would think they would want it. That may help explain all of the RFI problems you were having a while back. I would definately drive a ground rod anyway. Then put a red plastic fire hydrant above it so the dog would keep the soil as conductive as possible.

Slab

The NEC requires the neutral and ground to be bonded at only one place - At the service - and at that point the green ground is "derived" from the power company neutral (grounded conductor). The service panel should have a ground bus and an insulated neutral bus. The insulated neutral bus is bonded to the ground bus with a strap or bolt and that is the "bonding point"

The power company does not supply a ground - only a grounded conductor (neutral) if the NEC is followed.

The green ground sizes are determined from Table 250.122 and the size is determined by the breaker size ahead of it. Grounding conductors run from #15 for a 15 amp beaker to 800 kcmil for a 6000 amp breaker. The ground is sized to quickly trip the circuit breaker in a fault. The NEC grounding conductor is there for one and only one purpose - to provide a low impedance path for fault current - and so it may not work well at all for RF grounding.

There is nothing at all wrong with supplimenting the ground system - just don't tie it to the neutral except at the service. The ground bus in the service panel is tie to the system "grounding electrode" with a "grounding electrode conductor" which is sized from Table 250.66 and goes from #8 to #3/0 depending on the size of the service. The grounding electrode itself is composed of ground rods, ufer concrete encased grounds, col water main pipe and other specified available ground all bonded together.

The new 2012 code requires a minimum 2 ground rods unless a single one is measured a 25 ohms or less. This requiement is likely to change as it has caused an uproar in the contracting industry.

The local AHD in Spartanburg now requires a UFER concrete encased ground rather than a rod which is probably cheaper and a better ground. They require a minimum of 20 feet of copper wire to be incased in the footing as a UFER ground.

The AHD (Authority Having Jurisdiction) can require pretty much anything they want in addition to the NEC.

Pat
N4LTA

Pat,
      What is UFER? ? ?  That is a new one on me.

Also, I knew the ground was a fault path to trip the breaker in the event of a short or failure. But, I was also under the impression that it was also a "bleed off" for any slight leakage (capacitive coupling, resistive leakage, or insulation break down, etc.) to keep everything at ground potential and prevent electric shock / electrocution hazard.

the biggest difference between the ground and the neutral is that in normal operation the neutral leg is a current carrying conductor and the ground isn't.

In just about all cases, the ground conductor in a piece of cable (romex etc) is usually always the same size as the main conductors or 1 or so sizes smaller.

The 5 joined neighbors where getting RFI through the Neutral. It was identified here by inspection. Other then that issue, My station passed. Big power contractor style RFI filters for industial equipment solved that.  They have 80DB cut at HF and are available at electrical parts houses.  Its a good idea to install them into transmitters like George here.  Why even chance putting RF into your home?  Those neighbors rarely complained over the years anyays.  But since the inspection found it, I had to fix it.

A UFER ground is a concrete encased electrode developed for the army in 1942 by  Herbert G. Ufer.It makes a very good gound. Normally you have wire or a mat of wire placed inside the concrete foundation with a lead run out for connecting.

The grounding conductor does bleed of any small chage but the NEC developed it to conduct and dangerous current to the ground system and trip the breaker - it is all sort of the same thing.

I saw a system at a church here a few years ago, where the contractor bonded the neutral in every panel and thought he was helping matters.  The church has a CCTV system throughout the facility with multiple cameras etc.

The system was fed from multiple panels and each panel had a different ground voltage - quite a bit different due to current flow in the neutrals of each panel - and his bonds.

The coax had several amps of current flowing in the shields shields - because of the different ground potentials in the various equipment served by differnt panels. You would get a bad shock when removing a coax connector.

Pat
N4LTA

A concrete encased electrode ? ? ? ?  that kinda sounds like it defeats the whole purpose of the electrode  ???  ???

Concrete when dry is a very poor conductor, almost an insulator. Unless the concrete is some special mix with something conductive added to it. You would think some kind of non corrosive (rust resistant) metal in direct contact with the soil would make for a much lower resistance path.  Sounds like a trip to Google is in order..............




The shame of it all is that if you and everyone else had a neutral leg grounded with a good ground at the point of entry it would have prolly been a non issue!
the shame of it is that big RFI filters aint cheap and you got stuck paying for them.

Concret is always a bit moist when in the ground and a UFER is a very good ground. I suspect that the chemicals in the concete salt the ground also.

Pat
N4LTA

Churches have a special problem.

People with good intentions who volunteer labor.

Sometimes it isn't easy to balance.

I didn't know NEC was an evil plot to undermine folks with wire nuts and superior intellect.

I learn something every day. Thanks.

I saw a wire nut with a hole burned through the side once from being used in a junction and it overheated.

Pat, you keep dancing around NEC's forcing revisions when the old way worked fine for decades. Yes requiring 3 wire 120V outlets was a good move and a few other things that were cleaned up. GCFI was a good move also.
But most after that was a bunch of clowns in the electrical business looking to increase profits and creating new reasons to keep NEC relevant. Its the American way with any bureaucracy...form it, couch it in pseudo scientific psychobabble that the masses just blindly nod their heads, bend over, drop their draws and wait for the revelation ::) Pass out the Flavor Aid 8)

A lot of ham wiring is wrong and I mean potentially dangerous. Way too many use a basic 120V cable of 2 conductors and a smaller bare ground (called such as 12-2 "with ground") for a 240V feed since its cheaper....typical ham philosophy.

However using 3 insulated wires of the same gauge such as 12-3 allows the return current to run with out overstressing the wire. All the 4th wire does then is act as a backup while at the same time generating an annoying current between neutral and ground at the equipment end. That 4th wire is a complete BS requirement for probably 99.99% of single family residential installations.  It might be a bit high for double wides ;D

Also since existing wiring is grandfatherd for new appliances should tell you more about the con job. Im sure the always corrupt electricians unions would love to get the feds to require destruction of all non conforming structures. :P >:(

OH Carl!!!!!!!!!!

You are going to scream at this one. Even the inspectors are going off on this one

The new 2012 Code is going to be a bitch.

The new code is doing just exactly what you said.

ALL residential receptacles must be tamperproof and the ALL will have to be Arc Fault - which don't work well and are very expensive.
The real kicker is that in any age house - if a receptacle fails or anything else - it and everything downstream must be brought up fully to code.

That means if your wife yanks the vacuum cleaner cord and breaks the receptacle - you are supposed to call a licensed electrician and he must replace the bad receptacle and all on the circuit with $10 tamperproof receptacles AND install an ARC Fault circuit breaker at $100 bucks or so.

So that old 89 cent receptacle change out will cost $400.

There are lots of people POed and some things may change.


Maybe they will require a PE to sign off on house designs and I can retire a few years early? ;D

Nothing like our dear old government!!!

Looks like the AFCI circuit breaker's often but not always include a GFCI. That means George's power supply if there is ground current won't work once there is a AFCI breaker installed.

The following link discusses the complications the AFCI, and "false tripping". A case where multiple circuits share a Neutral in a junction box might require a home to be re-wired once AFCI breakers are installed. They neglect to say that the sixth reason for an AFCI trip is the Ham Radio guy next door!  ;D

http://www.thecircuitdetective.com/afci_circuit_breakers.htm

So if the AFCI circuit breakers have GFCI, then why not eliminate the separate need for GFCI's? All this stuff has a constant standby power draw.

Jim
WDJKO

Jim,

I think the AFCI breaker still cost too much and don't work all that well. The GFCI has been perfected over the years. The AFCI are troublesome. I think they work by detecting RF generated in an arc and lots of things in household have arcs - like hair dryer - when they switch off.

There has been an uproar since the last NEC (2012) was released because of some drastic , expensive changes and my guess is that some of the new stiff will change. The NEC is released and it takes about two years to get adopted.

The last code stopped the common practice of using a common neutral with three phase wires - when using each phase as a single phase lighting circuit or receptacle circuit - you can still do it but only if you use a three pole breaker. I had not heard about that causing the AFCI problems and that might be a reason for the recent change.

The biggie is requiring old homes and establishments to bring existing wiring to current code if something breaks. That is going to cause an uproar when it sinks in.

Carl is right on this new stuff - to much goverment for me.

Pat
N4LTA

Hi Pat,

     When was this adopted? I have this exact situation at work and requested the circuits be put on a 3 pole breaker. The electricians said it was up to code on discrete breakers. The circuits were installed in 2011.

Thanks.

It was added to the 2008 code I believe. The new codes take about 2-3 years to get adopted by the various jurisdictions. Some here are still using the 2005 code - so he may have been telling you the truth.

We had to change out all the lighting and receptacle breakers in an office building here last years because they renovated more than 50% of it. Had to change them to three pole breakers. I argued with the AHD but to no avail.

Pat

2008 NEC
210.4 Multiwire Branch Circuits
(A) General. Branch circuits recognized by this article shall be permitted as multiwire circuits. A multiwire circuit shall be permitted to be considered as multiple circuits. All conductors of a multiwire branch circuit shall originate from the same panelboard or similar distribution equipment.

FPN: A 3-phase, 4-wire, wye-connected power system used to supply power to nonlinear loads may necessitate that the power system design allow for the possibility of high harmonic neutral currents.

(B) Disconnecting Means. Each multiwire branch circuit shall be provided with a means that will simultaneously disconnect all ungrounded conductors at the point where the branch circuit originates.

Author’s Comment: There were two reasons for the changes to the text in this section. The first reason was to clarify that all conductors of a multiwire branch circuit must originate from the same panelboard or distribution equipment. The change in (B) was done to emphasize the safety concerns associated with unintentional voltage being present on multiwire branch circuits during maintenance. Deleting the text that applied simultaneous disconnecting requirements for a multiwire branch circuit to a single device or equipment on the same yoke will require simultaneous disconnect of all ungrounded conductors on any multiwire branch circuit at its origin.

Thanks again Pat. Time to push the necessary paper to get this done.....

The author's note sparked a bad memory literally.

Neutral from the panel feeds 3 separate 125 volt circuits from a 208Y.

I was installing emergency lighting and removed the wire nut from the neutral feed to a J box and the 3 loads. The other 2 loads were still energized. You know the rest.

Hey Pat, you just made my day!

From now on you can call me Outlaw Carl ;D

   So to enforce this, the stores full of 89 cent receptacles need to get rid of them, and make the repair installations by a licensed union electrician a mandate?

If so, time to stock up now, and as long as existing installations are grandfathered until broke, then I will just fix them as I go with NOS parts. So how was this intended to be enforced?


What happened to George?  ;)
Jim
WD5JKO

What will probably happen is that people that don't know about the change, when it's implemented, will get screwed when they call an electrician for a small fix and won't do it again.

The rest of us will never call an electrician again. I do careful work and do my research, lots of people don't have any idea what they're doing and don't really care. You'd be amazed at some of the nightmares I've seen, and fixed, over the years in friend's houses.

That said, I think work ought to be done well. I think the changes to grounded outlets, GFCIs and proper grounding/neutrals was a good thing. I may be convinced that new buildings should meet the new code.

Now I may have to buy some extra devices for spares. I already have "pre-ban" "assault weapons", unlocked scanners, R-12 Freon and 100 watt light bulbs. This is getting old.

Hey Carl -   I thought you might like that one.

From what I understand  - all residential receptacle have to be tamperproof as soon as the code is passed.

Now we will have to get all of out home receptacle from China undercover!


I think someone is actually making a cheap coverplate that converts the outlet - Its the AFCI that is going to hurt the pocketbook. It's also the retroactive clause in the that is all new.

Pat

Hmmmm........... scare people into creating shortages in order to inflate prices.
Kinda like the gas shortage from the 70s. then came the commodity shortages, that was another joke. Everyone was freaking out because there was going to be a shortage of TP next week. Then sugar the following week. First came the shortages, then the prices went up, then the shortages dissapeared..............

When we cleaned out my mother's house last summer I tossed 100lbs of sugar that she had stashed from the 70s. Concrete was softer than those bags of sugar. Not to mention a load of paper products that were so old they had turned brown.


And George, I think he got scared and ran away about 50 posts back   ;D

   Well back to ground current versus neutral current. I did a no-no recently at work. Needed to make a test bench for a 3kw 13.56 mHz industrial grade RF amplifier. So part of that was to test these dudes at +10% line, and -10% line from a nominal 3 phase 208VAC.

   The power was from a 'Y' fed 3 phase, and the RF amp is a delta load. The wiring to the room was to a Hubell 27XX 4 -wire 250V 30A socket. So all I had was three phases and ground...

   In a chassis I installed a 3 phase 15A 240V variac with the windings referenced to ground (the 4th wire). When the variac is on the dot (no buck or boost) the ground current is close to zero. When the load is 15 amps at 229 volts, or 15 amps at 187 volts, the ground current is 1.5 amps (10%).

   So I don't see any fire trucks coming, but I know this might not get a UL approval. How bad is it? I don't know the wire AWG of that ground wire, but I suspect it is hefty.

Jim
WD5JKO

the breaker my shack is on is one of those arc fault ones. i had an AA5 that i was working on one day and tried to hook a ground wire (the shack's earth ground, not AC ground) to it while it was turned on, had a small spark, and there goes the power. that small spark set the breaker off. i'd say that breaker may been a GFCI/AFCI combo breaker.
shelby

Jim,

The "Man" is looking for you for passing 1 1/2 amps through a ground wire!

Actually I need to think about that one a little.

The delta load has no requirement for a neutral and neither does a wye with balanced wye load

The variac should have three equal load wired in a wye connection that are balanced at any position.

In theory, your ground can only tie to the frame of the equipment and allow the center point of the wye float. The fact that you have 1.5 amps of unbalance that varies says it may not perfectly balanced or that you have some harmonic load but the amplifier should not care since it is delta connected.

Power companies often use ungrounded wye transformers. In fact almost all Duke Energy transformers padmount transformer are connected  - wye ungrounded :  wye grounded.  If you ask then for a "delta" 3 wire service  - the transformers are connected ungrounded wye.

All discussion here is BS and if you blow up a $25,000 amplifier I will not remember saying anything and will deny everything even you have witnesses.

I'll bet that if you remove that ground wire from the center of the variac - nothing will change


Pat

    Pat, you might be right! In the picture from the manufacturer, they had the variac commons bussed together. I went a step further and grounded that bus to the power ground. When I get to work next week I will do some experimenting.

  I hope some of this discussion helped George.

Jim
WD5JKO

Today I looked again at that 3 phase variac. Discovered that the clamp on ammeter was not closing all the way, so it was reading high. So closing it dropped the "ground" current to 1/2 ampere when the variac was boosting or bucking 10%. Put the variac in between (on the dot) and the ground current went to zero.

The load was 15 amps at 187V, and 12 amps at 229V. I got daring and disconnected the ground wire letting the three variac commons ride together, but not connected to ground. The picture of the variac in my last post is how the variac comes new. I did this first without any load on the power. It worked!
Pat your a genius.  :) I need to do a little more testing, but I think this is the correct configuration, and since there is no ground current, I suppose I am NEC legal.

Jim
WD5JKO

Now you don't have to worry about those AHD's sneaking around behind your back.

Pat
N4LTA

On the topic of "no-coders" sir, I did not test in the code element because it was not required and I did not have much interest in using CW at the time.

I have not intentionally ridiculed the subsets of which you are a member, especially the subset of CW-users, and therefore I have not ridiculed you personally by association.

What I have done is to have treated you (and everyone else here) with respect even though I do not know you, because I am a gentleman.

There seems to be a generational gap here.  While Im forced to accept the changes it doesnt mean I have to like them and individual personal insults were not intended.

You have to have been licensed for 20 years or so to understand where Carl is coming from.

It has little or nothing to do with CW operating.

Last time I went to a local Ham club meeting (5-6 years ago to upgrade to Extra - I had been an advance for 20 years and was too lazy to take the 20 wpm test). The new no code licensee applicants who were taking the Tech test,  went on and on about getting a free yellow jumpsuit if they "passed" the test and went absolutely ape sh$%t over me only missing one question on the Extra exam ( I was dissapointed in missing one  - since you can memorize all the answers by repeatedly taking practice exams on the net.)  About 1/2 of the appplicants failed the Tech test.

I enjoy CW but don't often operate it. I am a life member of the club, but I don't participate, because most of the activity is emergency prepardness and that is not what I want to do. Ham radio was once an area where you had to be a technical minded person to participate (to get licensed even).

The ham world is different today  - who can say worse or better.

Pat
N4LTA

At least 630M wont be open to voice modes but there will likely be a battle between CW and the digi chirpers ;)

Ok in that case no offense taken. I am 51. Not many generations to go. I've had the FCC general phone since '86 but not the ham ticket, that was only '95 or so.

This whole amateur radio thing got started on a bet. A friend kept goading me to get a tech license and he would also test at the same time but I did not want to bother with it.

Finally he bet me $100 that we could not get a certain habitual alcohol abuser, with whom we were well acquainted, to cram all night and pass the tech license the next morning. I had no choice in the matter but to cram the drunk all night and take the test with them the next morning.

This is my story of a lost-neutral scare.  My house was wired in the 30s, and the old wiring is two-wire no ground.  They  didn't even have 240v available until  they got an electric stove, and the third  wire was added between the house and the pole transformer.  Since then, circuits have been added, and those do have the 3rd wire ground.  Probably typical of old houses, where wiring has been added piecemeal over the years since electricity was first installed. Rewiring the entire house would require too much ripping up floors and ripping open ceilings and walls.

Shortly after we moved here, we had a new breaker panel installed, rated for 200 amp service.  The work was done by a licensed electrician, and the job was inspected and passed by the county inspector before power was applied.  The breaker panel was supposed to be a good one, made by a reputable manufacturer, Square D.

At the time, my ham station was still in the house, in an upstairs bedroom. I run the filaments and low power stuff off one  side of the line, and the 120v plate transformers run off the other.  That actually gives the tube filaments a slight boost when the plates are pulling current, since with a common neutral, a voltage sag on one side of the line causes about a 50% of-the-sag boost on the other.  There was a proper ground, tied to the house wiring ground, plus the rf/lightning ground I added for the station equipment.

I had used this for several years with no problem, until one evening when I hit the transmit switch, the lights in the room got so bright they startled me. Luckily, nothing was damaged; a lot of appliances and other stuff could have been wiped out.  I cut the mains switch at the panel and investigated.  What I found was, the panel had two separate neutral bus bars, held together with rivets, and only one of the bars was tied to the main neutral wire.  Over several  years, the riveted connection had corroded, and contact became intermittent or non-existent.  It hadn't caused any obvious problems as long as both sides of the line were loaded pretty close to the same.  But when I hit the transmit switch and the 1 kw plate transformer for the rf final plus the one for the modulator began to pull  current, the voltage on that side of the line sagged to almost zero, whilst the voltage on the other side of the line soared to close to 240 volts.  Luckily I immediately  noticed something wrong, and this condition existed only for a few seconds.

Instead of replacing the entire panel, or even hiring an electrician, I looked inside the panel and the cause of the problem was immediately obvious.  The bus bars were still hot to the touch, and there were black spots on the metal surrounding the rivets. I noticed several unused holes in each of the bus bars, so I took a piece of #10 scrap copper wire from the junkbox, cut it up into several short pieces  a few inches long, and used the spare holes in the bus bars to bond the two together with a half-dozen or so separate strands of #10.  That cured the problem, the electricity in the house was back in service within an hour, and that panel is still in service to this day, with no further problems. I'm sure a professional electrician would have insisted that the power be cut immediately, the panel be replaced with a new one at a cost of hundreds of dollars, and we would have been without power for at  least a couple of days. What really surprised me was that the manufacturer of the breaker panel would have bonded two neutral bus bars together at the factory with nothing but rivets instead of a securely connected heavy gauge strap.

I have a separate sub-panel out in the shack.  It is fed from an old 40-amp electric kitchen range circuit no longer in use. The electric range used two hots and combined ground/neutral.  I ran the cable out to the shack, using some 3-wire direct-burial cable given to me, that I put in plastic conduit anyway. The ground wire on that cable is insulated, so I use it for the neutral, carefully kept away from contact with ground.  The safety/RF/lightning ground uses a separate #4 solid bare copper wire, which is connected to an 8' ground rod at the shack, plus a run to the house where it is bonded to the main entrance ground.  I did not  run it inside the plastic conduit, but direct-buried it about 6" below the surface, like a ground radial, plus I connected several ground radials each about 20-30' long to the ground rod at the shack.

I notice there usually is a volt or so difference between the neutral and ground, as measured at the shack.  I tried temporarily shorting the two together with a clip lead, and there was enough current to make a visible spark.  I also noticed that with the neutral shorted to ground at the shack, it makes enough of a ground loop that audible hum appears in the receiver and transmitter audio equipment.

Now, all the audio equipment and low power station equipment is fed through a 120v isolation transformer with a balanced midtap. The midtap is grounded, so that each side of the 120v line runs at 60 volts above ground.  This has eliminated several pesky ground loop problems that had previously baffled me.

The problems and confusion involving grounds, neutral and associated safety issues would never occur if the US had adopted a standard from the outset to run everything off a single voltage (240v) balanced to ground, with a midtapped transformer at the pole and everything in the house bonded to a safety ground running to that midtap, so that the maximum voltage above ground anywhere in the system would have been 120v, but nothing pulling current at 120v, and there would be no need for a separate neutral and ground. But the national electrical system, like my house wiring, was assembled piecemeal over the years, so we have what we have, and it would be impractical to replace everything from scratch.

In the UK, do they do this? Or do they use one side at ground potential and the other at 220?

I'm guessing they have a center ground as the standard plug has three prongs.

The usual Euro power scheme is 220 V (not 240) single phase for residential service.  Hot & neutral + ground.   

Most of the service to the houses is done with big coaxial cable from what I've seen.  Very little metallic conduit, but a lot of that fat coax running everywhere.

The next step up is three-phase 380V, not sure about it being delta or wye.

Everything there is 50 Hz as well. 

There are several 'standard' outlet types in use throughout, so taking gear from country to country means adapters or changing the plugs on your cords.

73DG

You run a rig corded with two hots and ground without neutral return.  Even if there is a 120 v. load in the cabinet (but it is better if there isn't one) you run that paralleled to 1/2 of a 240 v. primary transformer that has a center tap (usually a big load like the plate supply).   You do not need, and in fact you should not have, a neutral return under these circumstances.

However, everything inside a rig powered by 240 v. service should be designed to operate off 240 v.   A very light load such as a few hundred ma. might not be a problem at 120 v.  The ground conductor regardless of its color is bonded to the cabinet and only that and is safety only.

In Europe the standard 3 phase voltage is 380/220  which is incidentially the same volts/hz as the USA. That means that a magnetic device is more or less interchangable ( athough this is terribly misunderstood and mis used)

You can run a 380 volt three phase motor on 460 volt three phase and it work just fine except at a higher speed. In fact - if you hook up a 480 volt motor on an inverter drive and run it at 50 hz speed it will have 380 volts on the terminal.

I often see European companies spending lots of money getting special transformers to run 380 volt motors in the USA - and they have problems  -  The proper terminal voltage for a 50 Hz 380 volt motor is 460 volts at 60 Hz. Same with transformers - the /Hz is important.

Also - I think most 220 volt single phase residential distribution is ungrounded - but I am not sure about that. I think the distribution voltage is 2 hots and no neutral - I'd have to check on that though.

Pat
N4LTA

I remember back in the 60s, in both UK and on the Continent, the outlet plugs were round, with two round prongs.  They all looked similar, but the spacing and prong diameter varied from country to country,  so they weren't necessarily interchangeable.  I suspect the ones in UK used standard English measurement (based on inches) while the ones on the Continent were metric.  Last time I visited UK, they had changed over to those gawd-awful things that looked like something you would use with a KW-1 or Johnson Desk KW.  They were heavy and bulky, with prongs that looked like they would handle 30 amps with ease; they used those things on EVERYTHING, even small desk lamps and electronic devices that might draw no more than 5 or 10 watts.  Don't know who the genius was who managed to come up with that idea.

I know they use 220 volts (or 240 or whatever), but not sure if it is grounded on one side, balanced to ground or simply left floating, and that might also vary from country to country.  If they had put me in charge in every country back when electricity was first being distributed, I would have decreed 220/240 volts balanced to ground, using two-conductor shielded wiring, with the shielding grounded and strapped to the midtap of the mains transformer. That would cut way back on ground loops and a.c. power noise, and would be less of a safety hazard.

I believe the standard here used to be 110/220v, but now it's 120/240.  I notice a lot of older stuff is marked "110".  I also see "115/230".  I think it's whatever the local power company decides.  Here, it varies anywhere from 105 to 125 volts, depending on the time of day and weather condx.  When we have abnormally hot or cold wx, with all the air condx or heaters running throughout the region, it is not unusual for the line voltage to the meter to drop below 110, but at other times it may soar above 125. I'm also aware that a lot of older radios were never designed to run off the higher line voltages that prevail to-day.

I have one of those little "Kill-a-Watt" meters, and it amazes me how poor the power factor is with almost any appliance I plug in, large or small. 0.60 is not at all unusual.

Here we have consistently high voltage. I've never seen it outside the range from 120 to 122 summer or winter.

But I live in the fastest growing city over 10,000 population in the US over the last decade, so most everything is new.

There are no above ground powerlines within 3 miles of my house, and 15 years ago the whole area was cow pastures.

Also, the distrubution transformer for several houses is in our front yard, so no voltage drop in the feed lines.

Those Kill-a-watts are cool. Fun to monitor things.

Dave

"Green ground" is a term used by electrical contractors and engineers used to describe what the NEC calls the "grounding conductor". The National Electric Code NEVER allows current to be carried in this conductor except under fault conditions. NEC and NEMA require this conductor to be green in color or bare copper inside equipment and identified with green tape in a raceway. The so called neutral conductor is called the "grounded conductor" by the NEC and must be white or natural gray in color or identified with white tape. To meet NEC requirements  - you must have a grounded conductor  - if you have phase to neutral loads (120 Volt loads) tied to the power system. If you have a 240 volt transformer with a 120 volt secondary winding  - that does not apply. The whole idea is that no current be carried in the grounding conductor (the green ground)

The standard in the USA is 120/240 volt single phase as the line voltage. Motors are rated 115/230 volts to account for voltage drop

The 3 phase standard is rapidly becoming 208/120 volts replacing the old obsolete 240/120 high leg delta where one leg of the delta had a center tapped secondary resulting in 120 phase to ground from 2 legs and a 190 volt high leg. The high leg burned out lots of equipment when it got hooked up incorrectely to a 120 volt load.

480/277 volts is the standard three phase voltage for large loads - the motors are rated at 460 volts -  again for voltage drop.

277 volt is used for lighting and some small single phase HVAC units. Generally in a large industrial facility the neutral is reduced as the 277 volt load is usualy small compared to the 480 volt load.

For even larger loads - 12470/7200 volts or 13,200 or 13800 volts is the standard although 2,000/14400 is becoming popular.

The old 4160/2400 volt medium voltage is obsolete but still in use on older systems.

Motors are common up to 13,800 volts three phase. Most large power plants use medium voltage generators - 13,800 is common and then stepped up to 230KV or 500 KV or even higher.


Common transmission voltages are 44KV, 66KV 115 KV, 230 KV 500KV and 750 KV.

Different power companied have different standards but most are pretty close to the above.

Pat
N4LTA

In the 50s, 7200v was pretty much the standard voltage for rural distribution systems. Most houses had a 3 kva pole transformer.  By the late 50s and early 60s the proliferation of electric appliances had overloaded those 3 kva pole pigs, and the power companies began replacing them en masse with something more like 10 kva's.  The old 3 kva jobs were usually sent to metal scrap yards.  Some power companies would sell them to hams, priced at their weight in scrap metal, just a few bucks each. This was back when copper was cheap. A 3 kva transformer, taken out of the oil and big can, made an excellent plate transformer for a 1 kw transmitter.  Many of them already had a midtap from the factory, so they worked great for full wave rectifier type supplies as-is. With others, you had to dig into the winding and try to find as closely as possible the mid-point of the HV coil, and bring out a tap.  Even after years of use, the stink from the transformer oil never quite went away.  Some hams would take them to a motor re-winding shop and have them dip the whole thing in varnish to kill the smell.  The power rating of a 3 kva transformer out of the oil was probably degraded to just about 1 kw power rating as a plate transformer.  Usually, some kind of variac or autotransformer was needed on the primary (formerly secondary) winding to reduce the HV to about 6200vct, enough not to arc over the 866As or 872As.

In the south it is interesting in how the distribution system developed. The first "high voltage" 3 phase sysem was a 2400 volt phase  to phase system. The distibution transformer was a 2400 volt to 240/120 volt transformer with two high voltage bushings. As loads grew the lines were soon loaded and the idea was to convert to a 4160 volt phase to phase system and use the existing single phase transformers connected phase to neutral  - many areas underwent a "conversion" in the late 60s to 4160 volts.

The loads continued to grow and now there is very little 4160 left - most lines converted to 12,470 phase to phase and used single phase 7200 volt transformer phase to neutral. Right after I graduated from college in 1973, you could buy 2400  and 4160 volt transformers for near nothing as systems went to 12470/7200. The city of Spartanburg, SC is still an underground 4160 volt system but it is heavily loaded and obsolete.

About 25-30 years ago 22000/14400 became the standard for new lines and now 12470  is getting old and dated. Voltages much higher than 22000 are hard to deal with for distribution especially underground cables although I worked on a 44KV cable system in 1974 but it was a transmisson line for a large factory.


Pat
N4LTA

A year or so ago I converted a old RCA BTA-1MX for operation on 160, although I don’t operate as much as I would like I do run the thing up at least once a week. Being that I thought I would not need 1 kW I decided to remove one of the PA tubes and also decided to run the plate transformer on 120 volts instead of the 240 volt design. The original design of the transmitter is 220/240 volts operation, all transformers, contactors and the blower are 220/240 operation. There are lots of tap on the transformers. Having a sub feed panel out in the shop providing a 220 volt feed and isolated breaker was no issue but the problem was that there was no provision for a neutral for the transmitter, just two hot leads and a service ground. I have a 240 volt 15A rated plug that connects the transmitter to the sub panel, that panel a square D QO load center has a isolated neutral from the frame ground that are all fed by an 8-4 cable back to the main panel where the neutral and ground are connected together. Being that I did not want to run the transmitter at full plate voltage I decided that I would remove the 220 volt feed from one side of the plate transformer and run the transformer on 120 volts. This gives me around 1.25 kV and an output of around 375 w from the transmitter. The problem is what to do with the low side of the plate transformer? There is no neutral brought to the transmitter except to the auxiliary lighting circuit and that’s just a little 18 gage circuit that supplies cabinet lights  so what I did was install a # 6 ground wire from the low side of the plate transformer to transmitter ground. There was already a heavy #6 ground to the station ground and # 12 grounds as part of the power cable to the sub panel. This has worked for some months without any issues and surprises me that I have no problems dumping lots of current back on the safety ground with any of the GFI outlets or anything else around the house. BUT because of this thread and because it never felt right returning current on the safety ground last weekend I changed the input to the transmitter. I got a 240 volt autotransformer and installed that on a panel above the plate transformer so now the 220 volt feed from the contactor connects to the autotransformer and that in turn feeds the primary of the plate transformer. No current flows on the ground circuit and everything again is 220 volt only in the transmitter. The only question now is there any reason that I would not want to run the plate transformer at its rated primary voltage?  I am assuming that a power transformer don’t care what its primary voltage is as long as it’s less then what would cause a insulation failure. Maybe there is some efficiency issue but so what if it’s not at optimal efficiency. Having a autotransformer or powerstat (what’s the difference?) on the input to the power supply is great because you can run power up or down with no issues and I have seen this done before in broadcast transmitters where they use a autotransformer to control the input to the screen supply for controlling power but on all the old AM broadcast transmitters have always seen the stupid system of inserting resistors in series with the plate supply output to drop voltage and reduce power that way. At least now my transmitter is not dumping current on the ground and NEC may be happy, next I will have to fix the back door interlock!

Hmm -  what impedance is that coaxial mains cable?

My first rememberance of a pole pig in ham use was a friend of my fathers who was an OT in the early 50's.
He worked 20 CW only with a SX-28 and chased DX with a 3el HB yagi just above the roof.The TX was HB to PP VT-127A's and they ran white at key down. Ive no idea of the voltage but it must have been a bit more than 1KW input ;D.

In the 70's and 80's when I was custom building single or dual 4X1 amps the 4160 pigs were the choice. I left the details to the buyers and gave them the pig in a can with schematic and parts list if wanted after demoing the amp on my PS.

Electrical safety may be a moot point when the utility meter explodes and burns the house down. Problem solved!
I don't know what kind these are that are exploding, hopefully not same as used here.
https://www.youtube.com/watch?feature=endscreen&NR=1&v=LXfIY6mfWWc
https://www.youtube.com/watch?v=ri-1nFkr5Ks

Well!  The 240 outlet has 2 hots and a neutral which is grounded with a 6 foot #8 directly to the incoming water main immediately below the fuse box.  The station itself is grounded directly to a cold-water copper pipe in the laundry room and to ground rods.  Everything is in the basement so the rods are driven immediately adjacent to the pipe inside.  The 120 outlets for the gear (which I wired and it was inspected) has hot, neutral and safety so they are standard 3-wire sockets on a separate 15 amp circuit.  

Since I have a recording studio, years ago I decided to add a sub-breaker box directly off the 240 mains.  That box has two breakers, both 15 amp.  One 120 volt side is designated "Control Room" and feeds all my recording gear.  The other is designated "studio" for artists to plug in amps.  Right now the only thing on that branch is the station.

As for the dryer, it has a separate fused line from the mains.  "George" the transmitter will have it's own fuses for each hot with the neutral going to the chassis/rack ground.  My main concern is dividing the various 120 volt supplies.  The only thing operating from 240 will be the PA plate supply which should run at about 1500VDC at 200 ma under load.  The modulator B+, both filament transformers, screen supply for the PA and its bias supply are all 120.

As far as the rectifiers, I'm sure using something from RF Parts Company or Silicon Alley would save space, but I already have the rectifiers on hand and space really isn't a consideration.  Thanks!  Mike-W9ZSL  :D

Mike,
Your Neutral should not go to the chassis.  Connect 120V devices between neutral and one side of the 240V circuit.  The only AC related wire going to the chassis should be the safety ground wire.  That safety wire then goes back to the ground bar in your electrical panel.  That in turn, back in the panel, connects to the neutral only at one point, hence no current will flow in the safety ground unless you have a voltage breakdown between a primary component and chassis.  In that case you will have "fault current" in the safety ground wire but only during the fault! 
Joe, W3GMS 

Pat could you further explain what is a tamperproof receptacle?  Are we talking special tools to "unlock" a receptacle?  Or a seal?

Is this really an insurance issue?  Joe the house owner replaces a "tamperproof" receptacle...the house burns down (for other reasons) but the insurance investigator notices the tamperproof receptacle was tampered with and...no pay!

TNX

Peter

This is a website that shows the Leviton tamper resistant receptacle and explains a little about them. It also states that UL had withdrawn its listing of the cover plate (cheap) type


[url][http://www.onestopbuy.com/Leviton-Product-Focus/Tamper-Resistant-Receptacles-36583.asp/url]


I really don't think that the insurance company can refuse to pay for code violations found after the fact.  - the mortgage companies would never put up with that.

 
Pat
N4LTA

OK TNX.  I had not heard of these type receptacles and was concerned that a homeowner could not "tamper" with a bad receptacle that had this rating.  Seems like a good idea to use them where kids are present.  For this kid, I'll have to resort to another method when sticking meter leads in a TR socket to see if it is live or what the voltage is ;D ;D

p

the stupid things cost more too - $5, not 89 cents. $7 if it is a combo light switch and outlet. If we are talking about the same thing, with the little blockage plates inside the prong-holes that keep only one object from being inserted at a time. Supposed to keep a child from inserting a fork tine in one side only. He now has to get two forks and stick them into both slots at the same time or they won't go in. Educational - forces the kid to do it right.

Here's the problem as far as I can determine.  My service panel is 3 wire with 120 on each side and wire #3 going directly to ground through the incoming water main.  The outlet for the dryer is 240 with 3 wires period.  Granted there will be a few ohms difference between the service entrance ground and the "neutral" at the dryer outlet and the station ground.  Unless the station was located at the service panel there will always be the possibility of ground loops because of the difference in resistances. That would be more important if and when I try to interface this transmitter with my recording studio.  At that point ground loops and RF feedback could become a nightmare.

For now though, balancing the current draw on either side of the 240 volt incoming power source is the key here...remembering that there are two HV supplies with 240 for the PA plate.  That can be ignored because it uses both sides of the mains.  I suggest that I can probably get away with putting the plate and filament supply for the modulator on one side and the filament, bias and screen supply for the final on the other.

The breaker boxes are the only places where the neutral is supposed to be bonded/grounded to earth, right? or not even there?

I would take it off that water pipe and drive a ground rod in order to avoid eating up the pipe from electrolysis.

   Mike,

  Consider using an autotransformer across the 240V balanced feed. Then use the CT as a local Neutral. This way all your loads will be balanced outside the rack. You can often pick these up surplus. Alternatively the 240/120V step up/down transformers available for powering  overseas equipment could be used similarly. The Frye's chain usually carries several options.


Here is one option, the Hammond 170GE 1500VA autotransformer:
http://www.hammondmfg.com/pdf/5c0073.pdf

Digikey:
http://parts.digikey.com/1/parts/997092-transfrmr-auto-115-230vac-1-5kva-170ge.html

Epay:
http://www.ebay.com/itm/Hammond-170GE-AutoTransformer-/230760162695?pt=BI_Circuit_Breakers_Transformers&hash=item35ba60a587#ht_1947wt_1181

Here is a 240V to 120V 500VA stepdown transformer for 50 bucks:
http://www.frys.com/product/3696575?site=sr:SEARCH:MAIN_RSLT_PG

Besides all the complexity with the 60 HZ ground current, loops etc. and the NEC, what about RF ground loops? Is this best a topic on another thread, or can George's thread handle this as well?  ;)

Jim
WD5JKO

Both the main power panel and the add-on breaker box are grounded at the service entrance through a short heavy ground wire directly to the water main entrance below it.  All outlets in the studio/shack are standard hot/neutral/ground types.  The cold water pipe goes directly from the meter under/in the floor of the basement then comes up in the laundry/furnace room about 25 feet away and branches out from there to the hot water heater and the rest of the plumbing.  My current station ground is connected where it comes out of the floor.  I have a ground rod just outside the basement wall in that same area under the eves so the ground is quite moist all the time.  The studio has a separate system grounded to a pipe near my equipment and even though I'm running unbalanced audio inputs and outputs I have absolutely no ground loops so I'm doing something right!  Maybe my best bet for the "George" project is simply use the ground rods alone for it.  As it stands the current station system works great and as they say, "If it ain't broke, don't fix it!"