Grounding Question

[W1RKW]

I posed this question to Tom, K1JJ and he suggested that I post it here.

I was messing around with a 10w transmitter over the weekend and when I was monitoring the output into a dummy load I noticed that I had an AC component on the envelope.  After dickin' around with my setup I came to the conclusion that I possibly have a ground loop.  What I discovered when I disconnect the antenna system from the shack the component essentially goes away.  The dummy load and antennas are all selected through an antenna switch.  When I separated the dummy load from the system so it was stand alone the AC component pretty much disappeared (only a slight hint of it on the scope like 10mV or less).

Here's the way I have my grounding setup.  I have a vertical and a dipole.  The vertical has a ground system.   The dipole does not. The vertical has a loading coil on it which ties to the vertical ground system at the base.  The station is grounded to a cold water pipe which is a very short run to the electrical utility system ground.  The two grounding systems are connected via the shielding on the coax to the vertical.  I think that's were my issue lies and I believe this is a no-no.  How does one ground the system so it's all at the same potential yet provide some lightning protection?  Should one run a heavy cable to the antenna system from the utility ground system?  Are there other ways to isolate the antenna system from the  station system without sacrificing antenna performance?

How do you gound all your antenna systems to the station?

Thanks.
Bob

[WA1GFZ]

I wouldn't isolate your antenna system ground. Say you are hit with a 20,000 amp  Lightning pulse and there is .1 ohm between ground systems. You then get a 2000 volt offset between grounds. Everything should be bonbed to the electrical ground.

[K1JJ]

  Are there other ways to isolate the antenna system from the  station system without sacrificing antenna performance?
How do you gound all your antenna systems to the station?

Bob,

I forgot to comment on that last point in our PM. The utility system ground or any other ground will not have a negative effect on a horizontal antenna's pattern or efficiency, connected or not. The exception is a beverage antenna.... see the thread about this. 

Pick a central point to put in a ground rod and then cad-weld everything to it via #6 copper cable buried underground. This includes the power utility pole ground, cable TV, telephone, your antenna coax shields, station ground, etc. 

Over here I ran #6 copper underground to all towers and utility grounds.

The only thing you don't want to do is ground the incoming well pump ground to this outside system (so I'm told) nor ground the 240 neutral from the main box thru the feeder to the ground in the shack. ie, You don't want a power line strike finding a minor path through your shack gear.  I made that mistake when I first started buiding rigs and had nothing but trouble with strikes. Now everything has been FB for at least 10 years.

 T

[W1RKW]

OK, so a nice heavy copper cable connected to the utility ground system and antenna.  That makes sense.  I guess what I don't understand is why the shield of the coaxes which are connected between the utility system and the antenna system don't do this.  Is it because the shield doesn't have enough copper to make a low impedance to the utility ground and minimal voltage drop between ground points and the whole point using a fat conductor is to reduce that impedance and voltage drop and ground loop situation and potential voltage drop in the event of a lightning strike?  As far as lightning is concerned though I do disconnect the feed lines from the shack.  This is confusing.  I guess dirt is a pretty good conductor afterall.

[K1JJ]

OK, so a nice heavy copper cable connected to the utility ground system and antenna.  That makes sense.  I guess what I don't understand is why the shield of the coaxes which are connected between the utility system and the antenna system don't do this.  Is it because the shield doesn't have enough copper to make a low impedance to the utility ground and minimal voltage drop between ground points and the whole point using a fat conductor is to reduce that impedance and voltage drop and ground loop situation and potential voltage drop in the event of a lightning strike?  As far as lightning is concerned though I do disconnect the feed lines from the shack.  This is confusing.  I guess dirt is a pretty good conductor afterall.

Ideally, you want the coax grounded before it enters the shack. At the tower, at ground level is perfect with a Polyphaser, etc.. 

I am able to ground my bare aluminum hardline easily outside, though you will need to use a connector/ junction or polyphasers type interface with coax to get at the shield without letting water in.

Yes, disconnect your antennas with the threat of T-storms... always.

I realize commercial stations of all kinds keep the ants connected, but they do have some major meltdowns too.

The best hamshack lightning prevention system I've seen is Chuck/K1KW's where he has quick disconnect connectors mounted on his plexiglass window. He goes outside and simply disconnects all rotator and antenna cables and drops them to the ground. (waterproofed, of course)

T

[W1RKW]

Looks like I need lay some thick cable in a trench. 

[KL7OF]

Tom, How do you keep from grounding the 240 volt neutral from the service to the shack?   It is bonded to the earth ground in the service can and all the BC transmitters have it bonded to the frame as well...I have the service ground rod and service pole ground rod tied into my central point shack/antenna ground system.  I use the large two bolt copper/bronze clamps.....they show a nice low resistance if I keep them tight... Do you use the therm-it chemical type cad welds?

[K1JJ]

For cad-welding I use those blue plastic tubes about the size of pill bottle. Get them at any electrical supply house. Pour the magnesium powder into a sand mold designed for the wire size and rod and light it with a spark. It reaches 5,000 degrees and leaves a bronze-type chunk of metal around the joint. Good forever. Forget soldering to a rod that gets buried underground.

Let me do some research on the neutral wire...

73,
T

[KB2WIG]

"I hesitate to give you much info, since I am simply parroting Al/K1JCL, who does professional installations of sites. He told me not to tie the 240VAC neutral to the station chassis grounds ....
 ... He said to connect only the fourth wire, the ground wire, to the chassis ground of the shack. "

This is standard NEC code...   a lot of confusion is that the ground wire and the neutral are grounded, but they are not the same thing.... One thing to rember is the neutral is a current carrying conductor; the ground wire is not.

There are several detailed analysis of grounding available;  the IE3 "Emerald" book is a good start. A good technical library may have a copy.  The am window has a fine section by the Polyphaser guy(s) geared generally for lightning protection. The type of books available at home depot, lowes etc., are fine as far as they go for normal home wiring.  I used to have a 800+ page hardcover text explaining the NEC, but I cant find it or remember the name now...   maybee in the near future....   klc   

[KL7OF]

Before there were 4 wire systems....the neutral was bonded to the service panel....The older 3 wire panels are in  more home services than 4 wire systems....That being said , I see that the 4 wire service cans have bonding lugs that effectively connect the neutral to the earth ground...........From our department of redundancy department..........when there are only 2 wires on the pole outside your house, how are the neutral and the earth ground separate?   Tom....I can't argue with the success that you have with regard to reduction of damage from lightning strikes by floating the neutral, but I can't figure out why it works.......Maybe someone on the FORUM can explain it....Interesting

[KB2WIG]

"when there are only 2 wires on the pole outside your house, how are the neutral and the earth ground separate? "

 They were't seperate-- the neutral was grounded.....




I'm a little confused with Toms 'floating' neutral.... I dont think its floated at all... I just dont know...   klc

[K1JJ]

Let me do some research on the reason(s) why the neutral should not be connected to station chassis ground thru the feeder drop ... and I'll get back. 
T

[W1RKW]

Bob,

I forgot to comment on that last point in our PM. The utility system ground or any other ground will not have a negative effect on a horizontal antenna's pattern or efficiency, connected or not. The exception is a beverage antenna.... see the thread about this. 

Pick a central point to put in a ground rod and then cad-weld everything to it via #6 copper cable buried underground. This includes the power utility pole ground, cable TV, telephone, your antenna coax shields, station ground, etc. 

Over here I ran #6 copper underground to all towers and utility grounds.

The only thing you don't want to do is ground the incoming well pump ground to this outside system (so I'm told) nor ground the 240 neutral from the main box thru the feeder to the ground in the shack. ie, You don't want a power line strike finding a minor path through your shack gear.  I made that mistake when I first started buiding rigs and had nothing but trouble with strikes. Now everything has been FB for at least 10 years.

 T

Tom,
OK on the polyphasor.  I was wondering how one would ground a coax fed dipole. Does the polyphasor only ground the shield side of the dipole or does it do both shield and center conductor.  I guess I need to read up on polyphasors. 

I think this maybe a repeat of what you just said but am I thinking correctly here, I can drive a new ground rod somewhere between the antennas and the shack and then tie the vertical antenna ground and utility ground to that new ground rod with the #6 wire then connect the shields of both feedlines to ground via a polyphasor near the shack which then connects to the new #6 wire, yes? And of course ensure all other grounds including station ground is attached to the #6 as well.  Should one use bare #6 or insulated or doesn't it matter?  I would think bare might be the better choice for a little "extra" grounding if directly buried and cad welded too.

This added protection would be good and proper but hopefully it will also eliminate the low level AC component I'm seeing on my scope.

Interesting on the well pump.  My well pump is grounded to the casing.  I wonder if that should be.
Thanks.

[w3jn]

Let me do some research on the reason(s) why the neutral should not be connected to station chassis ground thru the feeder drop ... and I'll get back. 
T

Because it's a direct violation of the NEC.

The neutral should be grounded at ONE place only - and that's the service entrance.  If youconnect neutral to ground anywhere else, you run the risk of not clearing a fault (by blowing a circuit breaker).   

The requirement to bond all auxilliary grounding elements to the service entrance is also a widely-ignored NEC requirement.  The reason is, as Frank implied, that heavy current flow (lightning strike or equipment fault) with a significant resistance between two grounding elements will necessarily create a voltage potential between them.

[Jim, W5JO]

You guys who use polyphasers for antenna grounds be sure to remember they are good for only so many cycles.  They should be checked periodically to see if they are still in place and not discolored.  This same rule holds for the MOV on your AC line input to gear.  After several years they should be replaced.

I have a friend in South Texas that installed polyphasers at the base of his tower years ago.  They had been installed about 5 years when we opened the case to look.  There was evidence that they had worked but there were burn marks and black soot all around in inside of the case.

[KB2WIG]

"My final question is how do GFCI units work?"

The GFI measures  an unballance in current  between the line and neutral. Kirchoffs ( i still cant spel this) current law. What goes in must go out. The breaker senses if the amount of current in the line side matches the amount of current returning via the neutral. If they are not equal, the remainder of the current must be going somewhere. At some point the amount of leakage,( say 5mA) trips the gfi (acting as a breaker)... The house breakers are there to protect the house wiring. The gfi is there to Specifically  save your donkey.

Specifically,  a wiring breakdown in the circuit that does not exceed the breakers current rating(s) will not trip. If the 'short' sources a few amps, it can kill you and the circuit breaker in the box doesn't trip. { just cause its a 20 Amp breaker, does not mean it will trip when it hits  a 20 Amp draw.... it may sit there cooking for a long time at 20 A. If your body draws the right amount of current, you muscles don't respond and you stay where you are. A friend was fininshing up a job, and was cutting out the nob and tube wiring with his dikes. His hand rode up  onto the metal part and this is where he found out that the wire was live. He said that he just stood there, unable to move, untill the wire broke, saving his life.

As we all know, it takes very little current to kill. If you are watering the lawn in your bare feet, and you move your outside speaker, which happens to have a little ac on it, the gfi may save your life.    As the story goes,the design engineer for the GFI had a pool party, called attention to himself and an extension cord with a lightbulb blazing, grabed ahold and jumped in the pool..  The no fry got his bosses attention... and now we got gfies.... 

I TTHINK the code wants 2 seperate GFIed ckts for pools,

 klc

[W1RKW]

Does a GFCI also look at voltage or current difference between the ground and neutral?  I heard somewhere that it was important to have all conductors of equal length otherwise a GFCI would not work properly (trip-off for no reason). 

The outdoor outlets on the front and back of my house are wired to GFCI's in the garage. Even though they are in weather proof enclosures on the outside the GFCI's trip-off in the garage when the weather is foggy and damp.  I've wondered what occurs in the circuit that cause the trip.

[KF1Z]

I've tried to suss out the electric company's wiring but can't quite get enough info via visual check. My first question is, where is the centertap of the power utility's pole transformer grounded? I do note some HEAVY gauge wire (often unsheathed up the pole and sleeved down lower on the pole)  running down the pole and into the ground, presumably to a buried ground rod or some other grounding apparatus. My guess from my inconclusive visual check is the centertap and lightning arrester at the pole are both grounded at the base of the pole.

My house was built in 1972 and has many of the limitations from that era of residential construction. My residential power feed uses a heavy stranded steel cable with two heavy insulated feeders wrapped around. My second question is, is the heavy steel cable the neutral feeder to my service entrance?

First question....

The CT of the transformer is "grounded" to the power company's "common ground line", (the second, or fourth wire running on the poles, always supposed to be the lowest wire).
AND, grounded through the wire you mentioned down the pole to earth.


Second question....

Yes, the bare wire, (usually alluminum) is the neutral..... if there's three wires total.
If there's four wires, then the steel is just a supporting messenger cable. and the neutral can be a sheathed wire, usually with a white stripe on it.
(assuming single-phase service)

[Steve - WB3HUZ]

GFCIs measure current flow, specifically the difference of current betweeb the hot and neutral conductors. Usually a sensing transformer is involved.

See here for a good explanation, to include schematics.

http://www.codecheck.com/gfci_principal.htm

[W1RKW]

Back to my grounding and AC on my scope. 

When I disconnect the antennas the low level AC component I'm seeing on the scope is reduced considerably but it's not gone unless I lift the ground on the scope.  The only thing I can think of at this point is I may have a ground loop being caused by the two AC circuits that feed the shack.  I have test equipment on one circuit and radio gear on the other circuit. My guess is when I connect the scope probe and ground the probe I'm completing a ground circuit between the two AC circuits in the shack.  And if that's the case what do I do to make it right?  I'm wondering if because one circuit has a longer run than the other and that there is a  potential being developed.  This is confusing and frustrating.