Bill,
Your branch circuit breaker is pretty small.
Are you energizing both transformers simultaneously? If so, it might help to
energize them individually.

The branch breaker can be up to 250% of the step up transformer's primary
rating. 10kVA/240V=41A.
41A x 2.5=100A. (round numbers). To do this you would also need overcurrent
protection on the transformer secondary. 

Of course, you've already got the 100A main tripping. That's why I asked if
you're
energizing them simultaneously. 

Transformer inrush can be a real problem. 

Hope this helps.

Dick Ratico
Solarwind Electric 

--- You wrote:
Friends:

I have on off-grid client that is trying to eliminate winter generator run 
time.  He has a rental on another corner of the property that has grid 
power.  When it was installed, he put in an extra meter, hoping to use it 
to run a utility back up feeder to charge batteries.

We are now installing this feeder.  We purchased two 10KVA 240/600 volt 
transformers to bump the voltage to 600 and then back down to 120/240.

Here's the problem:  when we energize the circuit breaker that feeds the 
transformer, the circuit breaker AND the main breaker trip.  The 
transformer is 10KVA, the main is 100 amps and the branch breaker is 
60A.  The breakers hold sometimes but trip other times.  This is obviously 
an inrush problem.  How do I correct this problem?

Thanks in advance,

William Miller
--- end of quote ---

