ac plug measurements

[N3DRB The Derb]

I made some measurements of the power outlets I've been trying to run my gear off of.  I have a ac voltage difference of 1.45 vac between the neutral and ground lugs of my wall plugs in the shack. These are the ones on the breaker that keeps tripping every time I key up.

I also have a 2.45 vac potential between the ground lug in the AC plug and my ground system coming in from outside, which is 5 8ft copperclad rods tied together with #6.

I really dont know what all this means as I know next to nothing about house wiring. Can someone explain these readings and if I have any sort of a dangerous situation?  I'm already bringing in electric guys but what do I need to tell them over the phone?

[W2PFY]

Derb, the first thing to do is go out to Homo Depot or Loews or Ace and get one of these testers. Make sure the one you get will test the GFI type wall socket. It will tell you  everything you need to know about a fault in the line and then you can call the electric guys and say this is what I have. They really work and I don't know of a good electrician that doesn't have one. The guys I see do the work test every socket with one of these. There's a chart on it to tell you whats wrong. I do all my own work and i wouldn't be without one. The cost is around $20.00 for the one that will test GFI's.

http://www.acehardware.com/product/index.jsp?productId=3099752&CAWELAID=167447823  

I Like the Home depot brand.

[N5RLR]

The neutral and ground of any [modern] 120VAC single-phase branch circuit should be connected together at the breaker panel, with no [or at the very least, minuscule] difference in potential between the two at a circuit terminus [wall outlet, lamp socket, etc.]

To my best knowledge [someone correct me if wrong] a GFCI shouldn't break or insert anything into the neutral or ground conductors, instead relying on an inductive pickup to sense a current fault to ground.  However, a long circuit run could result in leakage that could cause a breaker-type GFCI to trip when it shouldn't.  Wikipedia Article [click]

IIRC, the National Electrical Code requires all grounds [antenna, CATV, telephone, etc.] to be bonded to the electrical service ground at the point of entry, usually at the meter box.

A funky neutral/safety ground and an independent RF ground could be contributing to your GFCI woes, Derb.  Not to mention being a headache should an electrical inspector want to eyeball things [and be anal about it] in the event of a future wiring addition.

Perhaps replacing the GFCI breaker with a standard type and switching to GFCI outlets where necessary may be the way to go.

Just my 2¢.  Be safe; you and Glo have had enough on your plate for awhile, I'm sure.  

[Steve - WB3HUZ]

You'll want to tie your station ground and the power ground at the service entrance together with large conductor -#8 or bigger. Bury the run between the two ground rod. Even some of the aluminum stuff from RadShack would be OK.

I made some measurements of the power outlets I've been trying to run my gear off of.  I have a ac voltage difference of 1.45 vac between the neutral and ground lugs of my wall plugs in the shack. These are the ones on the breaker that keeps tripping every time I key up.

I also have a 2.45 vac potential between the ground lug in the AC plug and my ground system coming in from outside, which is 5 8ft copperclad rods tied together with #6.

I really dont know what all this means as I know next to nothing about house wiring. Can someone explain these readings and if I have any sort of a dangerous situation?  I'm already bringing in electric guys but what do I need to tell them over the phone?

[WQ9E]

Derb,

The voltage difference between neutral and ground you are seeing at your outlet is probably due to current flow through the neutral wire causing some voltage drop in this wire (since it does have some resistance).  There should be no current flow through your ground wire and thus your meter probe attached to that lead sees the actual potential at grounded neutral at the box while the lead attached to neutral at the outlet will see the voltage drop due to current flow between the outlet run and the box.  So you have a 1.45V drop in the neutral lead between your outlet and the box connection.  You will notice this amount changes with the load (i.e. plug in a "space" heater into the outlet and watch it change versus no load).   I would assume you are measuring this difference with some significant current loading of this branch circuit.

As Steve points out, your station ground should be bonded to the service ground at the main box.

Didn't you trace your GFI issues to RF?  I thought I recalled earlier that you were not tripping it when using a dummy load.

Rodger WQ9E

[N3DRB The Derb]

yes, but I dont have any confidence in the wiring job done by my ex-boss and we have some other work in the house for them to do outside the radio arena.

I just want to cover all the bases - I'm gettin real tired of the same old issues getting in my face.

[WQ9E]

Derb,

Understood and if the wiring is really done by Mickey Mouse count on the electricians taking some time to uncover all of the mistakes and undesirable shortcuts.  You are making the right decision to have them found and corrected rather than experiencing big issues in the future.

My sister-in-law at one point owned a charming older house but the previous owner had made some wiring changes in his later years.  There was a light switch in the basement with the old style metal outlet plate that was very hot to ground.  Tracing back the wiring to this he had transitioned from Romex to several different pieces of well used lamp cord so that he had enough copper.  He did do a fairly neat job of taping the connections but duct tape wouldn't be my first choice for electrical tape!  The good news was that the added wiring was in a suspended ceiling he installed so access for repair was excellent.  But it still can't compare to the gas well piping my well driller friends came across when a customer called for help with the home gas well their company had installed for a previous owner in the early 1950's.  At some point in time, much of the inside piping had been changed over to K-Mart garden hose including using regular screw on hose connections and hose repair kits as couplers.   The current owner was very upset that the inside runs had to be redone.

Rodger WQ9E

[The Slab Bacon]

Timmy,
         The more I think about and keep reading about this issue, and now the voltage difference. It really sounds to me like you have a loose / oxidized connection on your neutral line. or service ground, causing a ground loop when transmitting. I wish the hell I could get out here to help you, but I'm still too sick to even think about it.

[w3jn]

Try disconnecting your RF ground and see if that improves things.

I got some time I can probably get out there this week, help you w/the antenner etc.  Lemme know when's good.

[AB3L]

A 200 amp service would require a #6 copper ground. A 100 amp would require a #8 copper ground wire.

Reviewing:
The ground buss in your panel is the system reference point for all grounds, panel box, receptacle and switch box, water pipe.

The white neutral wire is the "current carrying return" referenced back to the same ground buss.

Until they tie back into your panel they are considered separate systems.

You could turn off your receptacle circuit, pull out the plug and check the splices making sure everything is tight and not corroded. Follow the wire back to the panel box or next junction point and do the same thing again till you get back to the panel.
You could also check the ground buss in the panel for good terminations at the screws and larger lugs. The aluminum service neutral can squeeze a bit in the lug on the ground bus. You would have to turn off all of the breakers to make sure there is no current draw there while you tighten it up.
***********
I suggest that you contact a good electrician to do the above. If you decide to do it yourself then you are on your own and responsible for your own actions.
***********

As to the aluminum wire suggestion.....I say stay away from it past the service entrance cable. Sounds like you are covered with the correct size ground anyway.
ALuminum wire sizing is different than copper, also important to know.

[N4LTA]

The grounded conductor (neutral) and the grounding conductor (green ground) have the same voltage only at the service point (where the bonding jumper ties both together). If there is any current in the grounded conductor (neutral) there will be a voltage difference which is the voltage drop in the grounded conductor (neutral).

Your station ground should be tied to the grounding conductor, water pipe ect.

Problems arise when the grounding conductor (green ground) has current flowing in it. The green grounding conductor should never tie to the neutral (grounded conductor) at any point other than the service point (the bonding jumper). This is where the jack-legs routinely screw up and only have one ground bus in downstream panels, rather than a separate ungrounded neutral bus, and a grounded ground bus.

Pat
N4LTA

[N3DRB The Derb]

Try disconnecting your RF ground and see if that improves things.

I got some time I can probably get out there this week, help you w/the antenner etc.  Lemme know when's good.

Super cool.   We can have a good feed over at the track!    Thursday we are going over there anyway. But normally I'm here in the daytime each day every day.   Frank, you need to stay home for now buddy.....but let us know when me and Glo can come visit?

I'm really pissed I missed the Heavy Metal show. I decided it was better to not JS around. The voltage difference between neutral and ground  at the plugs combined with the voltage difference between the ground plug and the station ground tell me I've got some funky issues going on. This is one of those times when I think you gotta call in the pros.

update: the pros are coming in @ 8am next Tuesday. Hopefully it will get resolved for good.

[KB2WIG]

Derb,
 Sometimes one has to bite the bullet and call in the experts.


klc

[k4kyv]

Some pieces of older equipment that operate off 240v use the same conductor for neutral and safety ground. Examples include the Gates BC1-T broadcast transmitter and the old electric kitchen range we took out years ago and replaced with propane. Maybe the electrical code permitted that back in the 50's and early 60's, but it seems to me to be an awfully bogus way of doing things.

I separated the ground from neutral in the Gates.  I used the abandoned electric stove branch circuit to feed the shack, but ran a separate #6 solid copper ground wire, and treated the 3rd wire in the original branch as neutral only.  I measure a fraction of a volt difference between neutral and ground at the sub-panel in the shack.  Once, I temporarily shorted the two together in the shack just to see what would happen.  I could see tiny sparks when I made contact, and with the two shorted together, it induced all kinds of ground loops that caused hum in my station audio equipment and even in the receiver. 

Shortly after I moved back here in 1979, a flaky contact developed between the neutral and ground buss bars in the main service panel next to the meter.  At that time the ham station was in an upstairs bedroom.  Once when I transmitted, the lights in the room lit up like an arc welder.  Turns out, when I keyed the transmitter, it put nearly the full 240 volts on the 120v leg on the opposite side of the line.  I was essentially operating the two legs in series, with no neutral connection whatever.  It's a wonder it didn't start a fire or at best, wipe out every appliance and every piece of electronic equipment in the house. I recall that when I took the front cover off the panel, the buss bars were too hot to touch.

Instead of spending a lot of money to have an electrician replace the breaker panel, I bridged the two buss bars together using about a half dozen pieces of #10 wire, attached to some of the numerous unused connection terminals on each bar.  The panel simply had the two bars riveted together at the factory, and when the connection got flaky, it heated up, and the oxidation process completely insulated one from the other.  And it was not a cheap off-brand panel, but a Square D unit installed by a licensed electrician and duly inspected.  I still use it, and after my JS repair job, it has given no more trouble.  I'm sure the electrical inspector would have in$i$ted on replacing the entire panel with a new one.

[N0WEK]

Electric dryers and ranges had a code exception that allowed them to use a combined neutral and ground since the timer, light and motor ran on 120 v in the dryer and different combos of 120 and 240 ran the stove top heating elements. Sometime in the 1990s, iirc, they changed the code to require separate grounds and neutrals and went to 4 prong plugs. The old stuff is grandfathered in, so most older houses still have the three prong plugs. When you buy a new appliance you have to decide on which cord to install.

The old system worked fine but the new one is theoretically better.

Any new wiring has to be the four prong kind.

[w3jn]

Tim let's shoot for tomorrow, mebbe around 11 AM or so?  I gotta go downtown DC for a going away for a co worker who's retiring, then Thurs we're prolly going up to the lake.

Lemme know if you need anything - parts pieces whatevah

[KE6DF]

I recently installed a cloths dryer in our home that my son got from one of his rental tenants -- it was abandoned when they moved out.

It was a fairly new dryer, maybe 3 years old.

Anyway, it came with a three wire cord. They had a jumper connecting the 240v neutral wire to the cabinet of the dryer.

I took out the jumper between the neutral and ground and then replaced the cord with a four wire cord which had a separate green ground wire.

Many years ago I got zapped removing cloths from a dryer. Somehow the hot line had worn or melted through and contacted the case of the dryer -- which on that old dryer wasn't grounded at all.

Ever since then I have been adding an external ground wire from the case of the washer and dryer to a ground clamp on the water supply pipe.

I suppose I was creating a ground loop in the case of three wire dryer connections like the one on this new dryer.

And, on top of that, new homes here in California now have plastic water pipe so grounding to a water faucet doesn't accomplish a thing.

I by far prefer four wire 240 connections with separate ground for everything.

If someone put me in charge of the electrical codes (not likely), I'd mandate it.

[N3DRB The Derb]

Sounds good! be great to see you again.   

hey, that other 75A-2, can I resto that one and keep it warm for you? Both of em will be ready to go and hot to trot when you come back for good.

bring that poor thing up here and I'll make hot munky resto love to it, come on.  It'll be tight, yo. 

[N4LTA]

Most new dryers and ranges don't come with a cord now. You have to buy the one that you need - a three or four wire. New construction must have a 4 wire feeder to a range or dryer.

A grounding conductor is not at ground potential if current flows in it. If you have a  security TV camera at one end of the house and the monitor at the other and have  - say 3 volts difference in the ground system  - then AC current will flow in the coax shield. If the coax shield resistamce is 10 ohms for the length - you can have  300 MA flowing down the shield - not a good thing at all.


Pat
N4LTA

[WA1GFZ]

200 amp service ground is #4 solid.
Derb, The more you talk about your problem the more I think the person who wired your panel wasn't smart enough to mount the GFI breakers on the the neutral bus side of the box. I bet the safety grounds are mixed with the neutrals causing voltage offsets. My panel the left gnd bus is the safety ground and the right side bus is the neutrals connected to the neutral lead to the meter socket. The neutral bus is connected to the safety ground at the bottom of each bus. Since the return currents go to the neutral lead there is no current on the safety ground,
Now if you have an older panel with 1 ground bus it would be easy to generate offset voltages between grounds depending on the return currents on the buss.

[N4LTA]

The busses are jumpered together at the service panel with a bonding jumper (usually a bolt) so while it is technically wrong  to do the above - it probably wouldn't cause a problem.

[AB3L]

200 amp service ground is #4 solid.

That's right, my bad. Work hasn't updated my code book. The '96 book that I looked at called for a #6, the illustrated '99 I found calls for the #4 so that must have been a rule change year. You may be grandfathered on the install. I better ask for a new book! I've been all fire alarm in recent years...thus the disclaimer.

[k4kyv]

In my shack, the 120v branch that feeds the receiver, vfo, oscilloscope and equipment in the audio rack is fed through a 1:1 isolation transformer.  The safety ground on the secondary side is not connected to the green wire in the rest of the building, but connects directly to an 8' ground rod just outside the building, which is also bonded to the radial system at the tower, and via a length of buried #6 copper wire, to the service entrance ground at the house.  Since the isolation transformer doesn't have a midtapped secondary, I created one by bridging a small midtapped choke outboard, directly across the secondary output.  That midtap connects to the local ground rod.  That way, the 120 volt line feeding all the station equipment except the high power transmitters has both sides balanced to ground, so that instead of having an neutral and hot, both current-carrying wires are 60v above ground each, and the 120v feeds to the equipment is treated just like you would treat a balanced 500/600 audio line, including all the ground loop and single grounding point precautions.  That eliminated some of the stubborn ground loops that had been causing hum in the audio equipment. I still have some daisy-chained grounds, so I am hoping that when I get those cleaned up it will eliminate the rest of the problems of audio hum and tunable hum in the receiver entirely.

Probably violates the electrical code, but it seems to work. An old Navy man told me that's the way the 120 v.a.c. lines are run on their ships. The highest potential difference between one of the wires in the a.c. mains and the metal hull of the ship would be 60v instead of 120, a safety issue in the wet salty environment of a ship.

[W7TFO]

Yep, balanced power for 120V is popular in studio environments.  There are at least two commercial outfits making the necessary isolation transformer, and are approved under NEC2005 IMHO.  Instant relief from ground loop hum.

dg

[N3DRB The Derb]

Mr. JN came over today and got my antenna back up to a normal height, an we troubleshooted the grounding issue but we didnt resolve it. I deduced enough info to make sure I get the electric guys pointed in the right direction