TRANSFER SW [RE-wrenches]

[Drake Chamberlin - Electrical Energy]

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Hi Wrenches,

We are setting up a transfer switch to run a house on a diesel generator in 
the event of a blackout.  The house now has a backup system consisting of 
two Trace 4048 inverters feeding an AC OUT backup panel.

The inverters AC 1 IN connections are fed from a breaker panel, that will 
get fed from the generator in the event that the transfer switch is thrown.

The generator now feeds the AC IN 2 terminals, and the grid feeds the AC IN 
1.  The inverters are in the SELL mode.  In the event of a transfer, the 
generator would want to feed AC IN 1 from the breaker panel, while the 
generator would still be connected to AC IN 2 as well.

The inverters would preferentially connect to AC IN 1.  But still we could 
have excess PV input trying to sell to a generator.

My solution is to have a contactor open the circuit to AC IN 1 whenever the 
generator is on,  so that the generator could only connect to AC in 2, 
which has no sell back issues.

My questions are:

1) What would happen if the contactor isolating AC IN 1 failed?    What 
would happen if the inverters tried to SELL power to the generator.  Should 
we use two contactors in series as a fail safe?

2) Being that the generator will take over loads,  does the contactor need 
to be motor rated?

3) Does anyone find any problems I've missed.

Thanks for your help.

Drake

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