abnormal Voltages

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Ksachs83

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Pasaden, Maryland, Anne Arundel County
This can be kind of confusing so just bear with me. I encounterd a power issue on a UPS supplied transformer. To not make this overly long I will try and sum it up. Metering at the main breaker of the panel, these are the voltages that I found:

3P-4W 120-208 system
A-phase to Ground-0v
B-phase to ground-210v
C-phast to ground-210v
Neutral to ground-120v

a-b 208v
a-c 208v
b-c 208v

The line side of the transformer reads 480 accross the board and everything is correct voltage wise there.

I had an outlet that stopped working and thats when i noticed the strange voltages and went back to the main at the panel. Just to verify I made sure I tested with a second meter and everything came out about the same. This was yesterday, today the voltages seem to be fluxuating almost like a lose connection point somewhere. In order to get the outlet working again and to be able to get 120v from phase-neutral I had to disconnect the ground wire at the device.

I guess my question is does anyone out there think this could be a ground/bonding issue at the load side of the transformer or could this problem actually be caused by the transformer itself. It seems to be localized to the panels feed from the load side of the transformer. I tested other outlets and equipment from the panel and it seems like this doesnt happen on anything feed from b or c phase but only on a phase. I am kinda scratching my head at the moment and Any insite would be appriciated.

thanks!
 
I think that most likely XO is not bonded to ground and phase A is faulted to ground.

I would start with checking the bonding out, that is a major safety issue.
 
one more question...If indeed the bonding is incorrect and its repaired, Do i have a potential for a fault condition on the transformer,or will this repair bring everything to normal. I guess what im trying to say is do I have a potential problem with the transformer since A-phase seems to be faulted?
 
It almost sounds as if there is an a phase fault--I would t/s it prior to re-energizing
 
Ksachs83 said:
one more question...If indeed the bonding is incorrect and its repaired, Do i have a potential for a fault condition on the transformer,or will this repair bring everything to normal. I guess what im trying to say is do I have a potential problem with the transformer since A-phase seems to be faulted?
Click to expand...

I doubt the problem is in the transformer, my guess is that a phase A branch circuit has faulted to ground. I also guess it is the circuit for the dead outlet.

Without XO being bonded, phase A touching ground would not be a short circuit, but when you bond XO and energize again it would be a short circuit

The correct thing to do is find the fault before energizing.
 
iwire said:
The correct thing to do is find the fault before energizing.
Click to expand...

The meter readings look pretty clear. With A phase faulted to ground: B to ground would be essentially B to A = (nominal) 208 and the same thing with C to A and also the reason for no difference of potential from A to ground. Is there, then, no SBJ?
 
ptonsparky said:
That would be my guess. Hopefully someone does not have it installed to A phase.
Click to expand...

Wondering and thinking on the fly....... Could it be a primary fuse on A phase transformer blown, check to see if one of the cutouts are laying open up there on the pole or fuse link appears to be dangling loose out the bottom of fuse holder.
 
mopowr steve said:
Wondering and thinking on the fly....... Could it be a primary fuse on A phase transformer blown, check to see if one of the cutouts are laying open up there on the pole or fuse link appears to be dangling loose out the bottom of fuse holder.
Click to expand...

Sure it could be but that could not change the ground to neutral voltage.

The bond is missing for sure.
 
iwire said:
I doubt the problem is in the transformer, my guess is that a phase A branch circuit has faulted to ground. I also guess it is the circuit for the dead outlet.

Without XO being bonded, phase A touching ground would not be a short circuit,
Click to expand...
As you correctly point out without XO being bonded, phase A touching ground would not be a short circuit, so it doesn't really account for the dead outlet.

iwire said:
The correct thing to do is find the fault before energizing.
Click to expand...
Completely agree.
 
Besoeker said:
As you correctly point out without XO being bonded, phase A touching ground would not be a short circuit, so it doesn't really account for the dead outlet.
Click to expand...

I did not say that a phase A ground fault accounts for the dead outlet. I am suggesting the dead outlet is strong clue where the ground fault is.

Here is how I am looking at things, there are two distinctly different issues.

1)The missing bond has been that way for sometime going unnoticed.

2)At some point an outlet went dead which was noticed.

Why would an outlet go dead? Well an open connection is a strong possibility and when you have an open connection there is a good chance the wire left hanging touches ground causing a ground fault.

Of course I could be wrong, there might be three different issues but I would look for the reason the outlet is dead and feel strongly in doing so I would also find the ground fault.
 
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