Upstream or downstream breakers for sub panel

generatorsubpanel

I have "recently" created an addition to my house here in CA. The original house had a 200 amp manual transfer switch for a backup generator, but this only feeds the old part of the house via a 100 amp subpanel, and I want to change things to feed the entire house.

The new part of the house also has a 100 amp subpanel. Each sub panel is fed via 100 amp breakers in the service panel and CU THHN/THWN(-2) wires.

If I feed the 200 amp transfer switch via a 200 amp breaker, ie remove the individual 100 amp subpanel breakers/circuits, is it a code violation to have the 100 amp breakers ONLY at the subpanels, aka downstream of the service panel?

I am looking at a cost effective way to allow the generator to power the entire house and I can't upgrade the transfer switch with additional poles or add breakers to it.

Thanks for any suggestions!

Please see diagram below:

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Connections are made from the load side of the 100 amp breaker to lugs in the switch using using CU THHN/THWN(-2) wires.

The same type of wire is used to connect the lugs in the switch to the orginal subpanel which is about 8 feet away inside the house.

Connections are also made from the load side of the other 100 amp breaker to the subpanel in the new extension to the house using CU THHN/THWN(-2) wires which is about 60' away.

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Best Answer

Often the stab rating of the circuit breaker mounting spaces are limited to less than the full rating of the busing, making it not possible to draw a single 200A circuit on the load side of the main breaker. I have seen combo meter panels that the meter feeds what is normal viewed as the load side of the main breaker and the stab connections feed the busing. Those panels usually have provisions for lugs at the top and bottom of the busing that could feed a transfer switch.

The conductors feeding both panels on the load side of the switch would need to be sized at 200A unless the length of wire satisfied one of the tap rules. An alternative might be to change the panel closest to the switch to a 200A, feed it with 200A wire and take a 100A load off it to feed the remaining 100A panel.

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