odd electrical situation

T

Tom Manchester

Senior
Jan 11, 2011
607
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Delaware
www.electrosoundsystems.com
Today I was doing some maintenance at my shop and decided it would be a good idea to map out all the circuits on the electrical panel.

So I went into the bathroom and pulled the cover off of the hot water heater. Then I put my meter probes on the incoming power so I could tell when I found the right breaker. I *thought* the hot water heater was wired at 240V, so I measured between the grounding screw and the white wire to see if I was getting 120V. Oddly though, it was at 26v. I measured between the hot and the grounding screw and it was 125V, so that looked normal. I thought maybe there was a bad breaker, so I decided to dig into the panel some more.

So upon opening the panel I traced the wiring from what I had determined to be the hot water heater breaker and confirmed that it was not wired at 240, but instead wired at 120. That made sense, but why was I getting 26v from neutral to ground?

Coming into the panel is a single phase feed from the meter bank outside. It has 4 wires, 2 hots, a neutral, and a ground. Hot to Hot measures ~250V, a bit high but not insane. Each hot to each neutral yields about 125 volts, so the neutral seems to be intact. Here's the kicker though, Neutral to Ground (they are not bonded in my panel) measures 26VAC! I went outside to the meter bank on the side of the building to investigate and I could not seem to locate a grounding rod from the meter bank panel. Where is the mystery 26v coming from?
 
Re: odd electrical situation

You have a leak somewhere. This happened at my shop on the blockheater cords going out the dock doors. One of the cords had been damaged and was leaking hot to ground something like 70 volts, but not at high enough current to trip the breaker. I found this out when my UPS was telling me "site wiring fault" on a completely different circuit. Check for damaged wire somewhere, bad cordcaps, extension cords, etc. Unplug everything you can, and hope that it's not some mice having lunch in the walls.

Edit: and the ground should not be going to the meter socket, it should be going to two ground rods buried somewhere, and also tied to a water pipe.
 
Re: odd electrical situation

Tom,

Is the panel you are working on a sub-panel? If not, neutral and ground *should* be bonded there. I.e. if you can trace the wiring from the panel to the meter then it's not a sub-panel.

Maybe take some pictures and post them, might help identifiy what's going on. That said, if there are *4* wires going to the meter, I'd be wary... that sounds like some kind of 3 phase system. 26v from anything to anything sounds odd though.

I'm not sure what Silas said is true though, the ground wire can sometimes be bonded to the meter box. That wire would be much different from the other conductors though (bare, and usually several gauges smaller). Are there 4 full sized insulated wires? Or is it 3 and a bare ground? Or more commonly, Type SE (two insulated conductors (hot) with bare neutral all inside an outer jacket) and an additional bare ground?
 
Re: odd electrical situation

Ryan Lantzy said:
Tom,

Is the panel you are working on a sub-panel? If not, neutral and ground *should* be bonded there. I.e. if you can trace the wiring from the panel to the meter then it's not a sub-panel.

Maybe take some pictures and post them, might help identifiy what's going on. That said, if there are *4* wires going to the meter, I'd be wary... that sounds like some kind of 3 phase system. 26v from anything to anything sounds odd though.

I'm not sure what Silas said is true though, the ground wire can sometimes be bonded to the meter box. That wire would be much different from the other conductors though (bare, and usually several gauges smaller). Are there 4 full sized insulated wires? Or is it 3 and a bare ground? Or more commonly, Type SE (two insulated conductors (hot) with bare neutral all inside an outer jacket) and an additional bare ground?
Click to expand...

Code requires the neutral/ground bond "at the point of service." Toms says his panel is fed from a "meter bank" which would be the point of service. The ground conductor comes from there, where it is bonded to neutral and ground electrode network.

The 26v. thing, though, is troubling because it indicates a non-obvious fault somewhere, like the one Silas points out.

Have fun, good luck.

Tim Mc

Powering the water heater with 120v. is surprising to me unless it's one of those 10-12 gallon units.
 
Re: odd electrical situation

If there is a meter bank (meaning a bunch of meters in an array in a box, then perhaps the bonding is done there instead of at each panel and the "ground" is going to the water pipe or ground rod through some pipe so it isnt obvious? Grounds are often green these days and not bare.
For a single meter single phase service there would only be 3 wires to the meter box.

If the service panel (breaker box) isn't the place of bonding the ground & neutral, then there should be multiple bus strips in the box. One or more for the neutrals and one or more for the grounds.

You may want the landlord to have the electric company open up the meter box to inspect things.
 
Re: odd electrical situation

as a rental/lease tenant, you have probably already gone further than you should have.

if there is indeed a problem, i'm sure the property owner/manager has a contract with an (qualified/licensed/insured) electrician. whether it's a 'simple fix' or not, you want it to be on their guy IF something goes wrong later on, as per your tenancy agreement.

R~
 
Re: odd electrical situation

Tom:
Have you measured the voltage on these lines with the Water Heater disconnected?
( I suspect the meter is reading what is called "ghost voltage" and can be disregarded with an additional test )
 
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Re: odd electrical situation

It's (kind of) funny you mention the water heater, because that's what sort of tipped things off for me to dig deeper. I was actually trying to find the breaker for the water heater because it's a big residential size unit and it's just sitting there wasting a ton of power when all I ever do is flush the toilet and wash my hands, so I deemed it an unnecessary expense. Apparently the previous tenant had an ice cream truck business and installed the larger water heater for washing utensils, and I must say they did a really crappy job on the plumbing.

So I'm pretty sure when I pulled the cover off the water heater near the heating elements, it said it was a 240V unit. Naturally I'm looking in the panel for a double breaker, or at the very least a pair of singles (i know, not to code) to shut it off. But low and behold it would seem that the guy had wired it to 120v service, as there is no tandem breaker :-/

Ryan: It's definitely 120/240v single phase, just like a house. There are 4 wires coming into the panel, 2 hots, a neutral, and an uninsulated ground. I think it's this way so that they could ground it back at the meter bank on the side of the building as opposed to individual ground rods in each unit.

The layout is as follows: Pole transformer > underground feeder > meter bank on side of building > service disconnect box on side of building > panel inside unit

If this were my own place I would dig further into the stuff on the side of the building and probably have this figure out in 10 minutes, but like Royce mentioned, my lease prohibits me from messing with anything beyond what I can meter at the outlets. I just can't figure where this mystery 26V is coming from. The only way it could be possible is if either the neutral or the ground were compromised somewhere, because theoretically if they are bonded at the service entrance they should be at the same potential.

I'll try what Silas suggested and turn everything off at the breaker and see if the voltage goes away, and then turn each circuit on individually and see if the voltage returns.
 
Re: odd electrical situation

If you are using a (typical) high impedance multimeter you can get a static voltage reading.
http://www.coleparmer.com/techinfo/techinfo.asp?htmlfile=Fluke-volt-affects.htm&ID=292

In olden days the typical low impedance meter would not read this.
One old timer method to determine if it's real is to include an incandescent light bulb in the meter circuit - If it lights there is power and a problem otherwise it a ghost reading.

BTW: This observation is NOT uncommon.
 
Re: odd electrical situation

Robert Burns said:
If you are using a (typical) high impedance multimeter you can get a static voltage reading.
http://www.coleparmer.com/techinfo/techinfo.asp?htmlfile=Fluke-volt-affects.htm&ID=292

In olden days the typical low impedance meter would not read this.
One old timer method to determine if it's real is to include an incandescent light bulb in the meter circuit - If it lights there is power and a problem otherwise it a ghost reading.

BTW: This observation is NOT uncommon.
Click to expand...

I had considered ghost voltage, but it seemed odd because it was measurable on all the outlets, and where the feeder comes into my panel. I won't discount it, and it seems like the article says it's possible, but 26V is an awful lot of voltage between neutral and ground.
 
Re: odd electrical situation

If the "device(s)" are still attached to the leg - the meter sees it...
Hence the question about load isolating ( switching breakers out ) and physically disconnecting devices.
The bulb trick across the affected leads will confirm the presence of dangerous power.
 
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Re: odd electrical situation

Tom Manchester said:
I had considered ghost voltage, but it seemed odd because it was measurable on all the outlets, and where the feeder comes into my panel. I won't discount it, and it seems like the article says it's possible, but 26V is an awful lot of voltage between neutral and ground.
Click to expand...

Seems to me your neutral and ground are not in fact bonded at the service entrance, and you're seeing a load imbalance either from your unit or a neighbor's.

Such as, say, a water heater hanging heavy on one side of the transformer.
 
Re: odd electrical situation

Robert Burns said:
If you are using a (typical) high impedance multimeter you can get a static voltage reading.
http://www.coleparmer.com/techinfo/techinfo.asp?htmlfile=Fluke-volt-affects.htm&ID=292

In olden days the typical low impedance meter would not read this.
One old timer method to determine if it's real is to include an incandescent light bulb in the meter circuit - If it lights there is power and a problem otherwise it a ghost reading.

BTW: This observation is NOT uncommon.
Click to expand...
And in current (no pun intended) days, a pair of "wiggys" (Square D Wigatron movement meter) provides enough load to make ghosts go away.
 
Re: odd electrical situation

As Rob mentioned a "wiggy" is not subject to phantom readings.
Wigginton ( solenoid ) tester predates digital meters and are strongly suggested for those who do electrical work frequently - especially power distribution circuits:
http://findarticles.com/p/articles/mi_qa3726/is_200405/ai_n9458300/

While stray voltage can't be ruled out in this scenario ( apparent bad wiring job ):
There are numerous cases of in which high phantom voltage is measured.
Often if excessively long runs are used, Or water heater circuits.
See NEMA Bulletin 88
http://www.nema.org/prod/wire/build/upload/Bulletin%2088%202003.doc.

Others ( like Klein ) make affordable solenoid testers.
 
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Re: odd electrical situation

If the meter bank has disconects in it,that is where the bonding should occur. Then the inside panel will then be considered a sub panel with grounds and neutrals seperated.What I have found when you get a low voltage reading between hot and neutral usually means the neutral is bad,ie: disconected,loose,coroded etc.
 
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