Down sizing a main breaker

[Bougard]

I have several installations where a fusible service entrance rated manual transfer switch will be installed on some buildings where the existing main breaker may be larger than the maximum fuse size of the fusible switch.

The engineer on the job is requiring these existing larger main breakers be changed out to match the smaller fuse size of the transfer switch.

Is this a requirement of the NEC?

 

[mdshunk]

Why? The fusable transfer switch will now be the service disconnect, and the old main panel will be a subpanel. That existing main will be little more than a local disconnect for that sub.

 

[steve66]

I would have guessed the existing service disconnect would feed the new transfer switch, not the other way around. Maybe the lower circuit breaker is needed to protect the wire between the existing disconnect and the new transfer switch?

 

[Bougard]

These are main breaker panels inside the building. The utility underground service wires are routed through the ct metering into the main breaker in the panel. I will be rerouting them from the ct's, through the transfer switch located on the outside of the building, and then back into the existing main breaker.

 

[mdshunk]

Now that you've cleared up the exact arrangement, I'll quote myself:

The fusable transfer switch will now be the service disconnect, and the old main panel will be a subpanel. That existing main will be little more than a local disconnect for that sub.