120/208 3phase

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Legrand

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I have a 120/208 panel that reads to neutral A=120v B=120v and C=131v. I don't think this is normal, I haven't taken readings at the mains but just wondering what could be causing this, I searched the forum and found suggestions for residential 120/240 services but nothing for 120/208.

Thank you
 
Legrand said:
I have a 120/208 panel that reads to neutral A=120v B=120v and C=131v. I don't think this is normal, I haven't taken readings at the mains but just wondering what could be causing this, I searched the forum and found suggestions for residential 120/240 services but nothing for 120/208.

Thank you
Click to expand...

What do you read ph-ph? Is it fed from another panel or just from a disconnect? Transformer type? I guess I'm asking for more info on your set up.
 
How long has this condition existed? Has a service transformer recently been changed? Any chance one has the wrong tap setting?

If you find the same at the service, it also could be that one of the POCO regulators is pegged/stuck as they can regulate +/- 10%. The controls occasionally go haywire and the regulator has to be manually set until it can be fixed.
 
This is a sub panel, I don't quite remember phase to phase readings, I will be back in there today, I will also check the main, I have no idea how long this condition has been present I just found it this week.
 
Ok so the building is fed from the utility with a 120/208 service, it's huge, I didn't take a reading at the main, I was by myself and I'm a sissy la la. I did take readings at the sub, I hope this helps, (I may be able to read the mains tomorrow). Could this be because of an imbalance on phases or....utility problem or......? I'm lost.
A-B 208
A-C 218
B-C 219

A-G 120
B-G 120
C-G 131

A-N 119
B-N 121
C-N 132
 
Given your readings, I stick with my post #3 for the time being.

I'm thinking a POCO regulator problem or you have a transformer on the wrong tap. It would be useful to get the voltages at the service when you get a chance.

Is there a transformer between your sub-panel and the service?
 
I guess another problem could be the local voltage drop but that is a big imbalance.

What is the current for each phase at the main?
 
DP520

DP520

Check to see if the XO bonding jumper to the frame is good. I had a guy set a 120/208 3ph 112.5 kva transformer and he did not remove the paint from the case at the bonding point of X0 same thing.
 
DonP520 said:
Check to see if the XO bonding jumper to the frame is good. I had a guy set a 120/208 3ph 112.5 kva transformer and he did not remove the paint from the case at the bonding point of X0 same thing.
Click to expand...
A missing or poorly connected system bonding jumper would normally show much different voltages when you read from line to neutral and from line to ground. The voltages here are almost the same between line and neutral and line and ground.
 
Legrand said:
Ok so the building is fed from the utility with a 120/208 service, it's huge, I didn't take a reading at the main, I was by myself and I'm a sissy la la. I did take readings at the sub, I hope this helps, (I may be able to read the mains tomorrow). Could this be because of an imbalance on phases or....utility problem or......? I'm lost.
A-B 208
A-C 218
B-C 219

A-G 120
B-G 120
C-G 131

A-N 119
B-N 121
C-N 132
Click to expand...

With readings like these, I agree with mivey. I would check regulator panel first. You can check it if you find a service on the c phase somewhere down the line. If a single phase service on the same phase as the one with the 131 volt reading has the same 131 volts, tell the POCO to check their regulators.
 
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