XFMR Short/Trip

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sullyelectric

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I am an electrical supplier and one of my customers is stepping up from 208/120 to 480. They tell me that when they turn the breaker on it trips.

I told them to disconnect the 480 side and it still tripped.
I told them to disconnect the 208 side and turn the breaker on and it stayed on.
This is the second XFMR that i have given them.
There is nothing connected to the XO and the system is not corner grounded.
I asked them if maybe they were feeding using a single phase panel but they said it was three phase.

Any ideas on why it is tripping?
 
sully,

Is it fed with parallel conductors ? Possibally identified a cable the wrong
phase.
If it is still disconnected at the tranny (primary) it would be easy to ring out
the feeders or meg. the conductors out.
They did hook up the 208 to the 'X' terminals, right?
So they have a 208 to 480 ungrounded system.
 
sullyelectric said:
Any ideas on why it is tripping?
Click to expand...
If this is a step-down transformer being used in reverse, it may very well be inrush current.

What is the transformer capacity, and what is the rating of the breaker supplying the circuit?
 
Frank & larry have mentionted the most obvious.
(a) make sure he has wired the 208 to the LV (X) terminals and NOT connected a neutral to XO.
(b) they may not be taking "inrush" current into consideration.


Note: I'd bet on (a) :smile:


A defective factory transformer is a rare bird indeed.
Far less prevelent than a dfective install.
 
I'd cast my vote with Larry...

I'd cast my vote with Larry...

Most likely, (assuming qualified electricians with the ability to read a nameplate are conducting the installation), the CB is mismatched to the Transformer. I simply can't believe 2 new transformers would fail. I also believe a person will always try to conduct the best work possible, before telling someone it has a failure.
 
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