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#7397 02/03/02 04:04 PM
Joined: Nov 2000
Posts: 2,236
Likes: 1
Got a troubleshooting call today, seemed to be a typical bad neutral scenario, but something odd was taking place.

I was reading 117V on one leg and 127 on the other (to ground) and 244V between them, with all circuits on. With all circuits off, it stabilized to 122V per leg, with 244V between them, which is closer to normal for around here. I elimated the circuits one at a time until I was down to the 120V pump circuit and a bedroom light/receptacle circuit that appeared to be the culprits in bringing down the leg that drops 5V.

My question is: what is making the other leg rise by 5V at the same time, when these circuits are not multiwire, and no other circuits are effected?

I'm still thinking a bad neutral, but where?

Wouldn't a bad neutral effect every 120V circuit in the house, either rising it or dropping it with respect to the resistive loads?

[This message has been edited by sparky66wv (edited 02-03-2002).]

Residential/Commercial Inspector
5 Star Inspections
Member IAEI
#7398 02/03/02 05:01 PM
Joined: Dec 2000
Posts: 4,294
Sounds like you've lost the ground on the service. No reference point for the neut., or the neutral is open somewhere. Heck I dunno! [Linked Image]

[This message has been edited by electure (edited 02-03-2002).]

#7399 02/03/02 05:05 PM
Joined: May 2001
Posts: 717
This is the classic symptom of a transformer with no reference point ie: It is not earthed anywhere. If inside, check to see if the bldg steel is grounded, your gec is still tight and existing, X0 has not been compromised, etc.

#7400 02/04/02 10:58 AM
Joined: Nov 2001
Posts: 280
Sparky WV
I would check for corrosion on the neutral buss. I run into these every once in awhile, one that stands out was a house with half the circuits not working. The panel was mounted right next to the dryer and the exhaust tube for the dryer ran right over top of the panel. There was corrosion so bad that they would lose a different ccircuit almost everyday.
It was one of those made by siemens but was not a siemens (cant remember the name) but the neutral buss on the other side of the panel was fine and relocated all the neutrals to it. and all ccircuits came back up. It was really screwy the worse the corrosion the more circuits dropped out.
Good Luck

#7401 02/04/02 11:38 PM
I would have to agree with George on this one. It sounds like your transformer neutral is floating. What you are seeing on on the loaded voltage readings are an unbalance in the load. This causes the "virtual" neutral in the transformer to "shift" a little left or a little right depending on which leg is loaded more. This is why transformers are grounded on the center tap. It gives a reference point and defines zero volts within the transformer. When the load is removed, balance is restored, and the voltages equalize. I would do a visual inspection on the transformer to look for loose or missing wires. The PoCo may need to check this out for you. I do not see how this problem could be inside the residence since the transformer is grounded at the pole.

#7402 02/04/02 11:59 PM
Joined: Nov 2000
Posts: 2,236
Likes: 1
I tightened up all the screws in the panel, but it didn't seem to help. The lady had to go to work and I wasn't able to look into the disco yet, but from what I'm understanding here, is the ground reference at the Xformer is being lost, rather than an impedance in the neutral on the load sides...

The pump has an unusually long run with #12-2-g Romex draped through the trees, so it is under suspicion too...

Residential/Commercial Inspector
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#7403 02/06/02 11:38 PM
Joined: Oct 2000
Posts: 2,723
Likes: 1
Broom Pusher and

Sounds like a common situation where L-N loads on "One Side" of the Xformer's coil have very little Capacitive Reactance [Xc] - loads are more true power, and the other side has high Xc loads.

The higher Xc side would have higher voltage, and the most likely culprite would be Induction Motors running with very light loads [or no loads] on their shafts.

Another reason would be a Transformer with high Impedance [like + 5.0% Z] which has a poor load balance deal going on.

Anyhow, this should not be a big problem until the RMS voltage under a load situation begins to exceed 135 VAC L-N and 260 VAC L-L [using a high loading effect volt meter - one with a low input Impedance].
That's when the smoke begins to spill out [Linked Image]

Always remember those DVMs might show above RMS values, with a response to the level of current drawn at a high input Impedance - equaling out to a higher than actual voltage readout!

Please pardon zee bad spel-eeng! [Linked Image]

Scott S.E.T.

Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

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