Suggestions ???

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ElectricianJeff

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Southern Illinois
I am in the process of installing some interior and exterior lighting, recepts and switching in a large detached building. About a third of the way through this process the owner mentioned that sometimes when the kids come in the from the pool with wet feet and touch the refrigerator they feel a "tingle".

What I found was the house has a 320 amp. undergound service with a 200 amp panel located inside the home. The service is grounded at the meter socket with rods, all plumbing in the house and the outbuilding is plastic. There is a 200 amp. disconnect on the exterior of the home which then feeds underground in 2" PVC about 50' to the outbuilding. The feed is 3-wire 3/o copper to a 200 amp. load center located inside the building. The grounded conductor and the EGC's are landed together on the neutral bar in the panel with no additional grounding present. I pulled the EGC on the refrigerator circuit and got 18 volts with the frig. running.

What I would like to do is pull an additional EGC from the main service, install rods, isolate neutrals and grounds at the building panel, however I don't think pulling the 4th conductor is going to be feasible with the owner.

Do I have any other options here that I am missing? This property is way out in the boonies, no permits or inspections. They don't even have zoning yet. If they even have an electrical code it's not the '08.

Most of my experience has been in new construction so we just did it right from the getgo. Should I be looking anywhere else for the source of this unwanted voltage? Pools, kids and electric scare the heck out of me since a 12 year old girl was electrocuted last summer about 30 minutes from where I live. Any assistance on options on this would be greatly appreciated on this end.
 
It sounds like you have an internal problem in the refridgerator as well as the other problems with the electrical system they have, run an extension cord from the main building and see if the problem still persists, they probley need to have the fridge repaired or replaced.
 
ultramegabob said:
It sounds like you have an internal problem in the refridgerator as well as the other problems with the electrical system they have, run an extension cord from the main building and see if the problem still persists, they probley need to have the fridge repaired or replaced.
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Thanks, I'll check that. The HO mentioned they have the same problem when they touch a large floor type fan, I only checked the frig. circut but will check the other circuts when I return.
 
ElectricianJeff said:
There is a 200 amp. disconnect on the exterior of the home which then feeds underground in 2" PVC about 50' to the outbuilding. The feed is 3-wire 3/o copper to a 200 amp. load center located inside the building. The grounded conductor and the EGC's are landed together on the neutral bar in the panel with no additional grounding present.
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That has been code compliant until the adoption of the 2008 NEC.

I pulled the EGC on the refrigerator circuit and got 18 volts with the frig. running.
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Can you explain this more, where did you place the meter leads?

If it was between the source EGC and the refrigerators EGC the refrigerator has a problem and should be serviced or replaced.

It will trip a GFCI if you install one.


What I would like to do is pull an additional EGC from the main service, install rods, isolate neutrals and grounds at the building panel, however I don't think pulling the 4th conductor is going to be feasible with the owner.
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In my opinion that is not likely to fix the problem.
 
iwire said:
Can you explain this more, where did you place the meter leads?

If it was between the source EGC and the refrigerators EGC the refrigerator has a problem and should be serviced or replaced.

It will trip a GFCI if you install one.




In my opinion that is not likely to fix the problem.
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I pulled the egc from the refrigerator circut and tested back to the neutral bar.

Are you telling me that the refrigerator is the only problem with this install? I just want to be clear on this.

Thanks
 
Based on your posts, I have the same answers as Bob.
This is not an illegal install as per past code cycles.

It sounds as though there may be an issue with the fridge itself...if it is older, I would not be surprised. The same may be for the fan.

If you want to test the circuits, use an extension cord from the house to plug in the fridge and check that out.

I also agree that the fridge is going to trip the GFCI.
 
080614-0749 EST

ElectricianJeff:

What kind of floor in this outbuilding?

If concrete, then it may be a good conductor. A concrete floor will have a potential of the earth with which it has contact.

I just ran a simple experiment. At a work bench in my basement I measured the voltage from neutral to the concrete floor using a Fluke 27 and just the test lead probe tip against the concrete, also used a penny as the contact point. With the computer running the voltage was about 0.2 V. Added a 10 A load and the reading was in the range of 3 V. Using an old Simpson 260 with 1000 ohms/volt on AC the readings were much lower. I have a sealer coat on the floor. Thus, capacitive coupling was probably a significant factor in the difference. Neutral to EGC was about the same as the Fluke to floor.

If you run an extension cord from the house to the outbuilding you can use the EGC of the cord to provide a ground reference from the home. Make all measurements using the home EGC conductor as your reference point. Measure the neutral voltage at the outbuilding, and voltage to any items or surfaces that one might contact. From these voltages you may be able to identify the problem.

Also check the voltage of the earth around the outbuilding and the pool.

With feet in a pool of water what voltage at wet hands will cause a tingle. I know 6 volts will do it. This is from personal experience on a hot humid day with sweaty hands touching the horn ring and car chassis. Normally my hand to hand surface resistance is about 500,000 ohms. It was much lower in the horn ring case.

If the floor voltage is different than the outbuilding EGC, then this potential will be the tingle voltage between floor and a device connected to the outbuilding EGC. Note: the outbuilding EGC and home EGC will differ in potential by the voltage drop on the neutral betwen the two locations.

The earth voltage at the outbuilding may differ from the outbuilding EGC if there are leakage sources to the earth.

.
 
Check from the frame of the refrigerator to the neutral bar in the panel, if you have the 18 or so volts between there, the equiptment ground is open somewhere on the circuit. This still means you have an issue with the fridge, but explains why they are also getting shocked off of the fan. If you do not get the 18 volts, unplug the refrigerator and check again, if you are getting the voltage again ,it's not the refrigerator, it's coming from another source. Turn each breaker off one at a time until the voltage disappears, then you have found the circuit that causing the problem, troubleshoot from there on to narrow down to the culprit. If it does not disappear, turn off the feeder to the panel and check again, if that does it then the feeder has a fault in it.
 
I realise that this installation was code compliant when installed, but if the fridge is working properly what stops this from just being a shock caused by a little bit of neutral-current flowing through a parallel-path when the kids touch the fridge with wet feet? Seems like folks are discounting that and I don't understand why. Is it just more likely that the fridge has a ground-fault?

-John
 
If you are reading voltage from the disconnected groundwire in the panel to the neutral buss, you have some type of voltage bleed inside the refridgerator or the cable feeding it, there shouldnt be any continuity between power or neutral and the metal case of the refridgerator. its probley not enough contiunity to check with a regular meter, you would probley have to use a megger.
 
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big john said:
I realise that this installation was code compliant when installed,
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John, if we say that the original installation is unsafe that is the same as saying every service in the USA is also unsafe as both use the neutral as the grounding means.
 
three wire feed

three wire feed

If it's a 3 wire feed to the out building then there should be additional ground rods driven. I don't think that that will fix the Refrigerator but.....
 
iwire said:
John, if we say that the original installation is unsafe...
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But we aren't saying the original is unsafe. While I would prefer a separate EGC, I don't think it's a serious hazard. I'm just asking if this isn't a normal side-effect of a bonded-neutral: A parallel path through the wet kids giving them a little zap?

-John
 
big john said:
I'm just asking if this isn't a normal side-effect of a bonded-neutral: A parallel path through the wet kids giving them a little zap?

-John
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In my opinion no.

If it was likely then people would be getting little zaps off the meter sockets at the service.

Of course I assume the conductors and connections are in good condition.
 
big john said:
. . . but if the fridge is working properly . . . .
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On what basis would you claim that the fridge is working properly? On the fact that it still keeps stuff inside cold? It could do that, and also have a wiring problem, in which case I would not call its operation "proper."

I should have thought that,
(1) If there is an 18 volt difference between a point on an EGC and a point at the panel to which the EGC is connected (N-G bond at that panel), and
(2) If that voltage is imposed along a wire (namely, the EGC for the circuit serving the fridge) and nothing else is in series with that wire, and
(3) If that wire has a very low resistance (as of course it would), then
(4) There would be so much current through the EGC that it would trip the breaker.

What am I missing here?
 
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