We have a customer owned transformer at a gas Compressor site, so primary metering applies. The service disconnect will be a fused disconnect switch in the primary circuit between the utility meter and the transformer. This disconnect switch will be located about a half mile from the transformer, and close to the utility meter (pole mounted) at the station entrance road. The secondary of the transformer will feed an electrical building (MCC) that's located approx 400 ' away. A generator (with circuit breaker) and an automatic transfer switch will be located near the transformer, with the automatic transfer switch feeding the electrical building from either the generator or the transformer (utility).
We'd like to make sure we have the proper protection for the feeder conductors running from the transformer to the transfer switch, and then from the transfer switch to the electrical building, while also meeting the requirements of NEC 225.31: Disconnecting means.
Since the service disconnect is already located in the primary circuit of the transformer, I believe the transfer switch does not have to be "service entrance" rated, and so is not required to include a circuit breaker (for the utility power from the transformer).
The generator already includes a circuit breaker, that will protect the conductors from it to the transfer switch. These conductors have less current capacity than the conductors from the utility transformer.
My question then is if we install an incoming feeder circuit breaker in the electrical building (MCC), will this breaker protect both the incoming conductors from the transfer switch to the electrical building (MCC) and the conductors from the transformer to the transfer switch ? Does the fact the Transfer switch and transformer are approx 400' away affect code compliance for this ?
Or should we instead install a circuit breaker in the transfer switch (and not in the electrical building/MCC) to protect the conductors from the transformer to the transfer switch and from the transfer switch to the electrical building (MCC), which is 400' away. If we do it this way, will we need to install a disconnect switch in the electrical building (MCC) for the incoming feeder conductors ? or will the breaker in the transfer switch qualify as the disconnect switch for the feeders into the electrical building (MCC) under NEC 225.31 ?
Would appreciate any comments on this.
We'd like to make sure we have the proper protection for the feeder conductors running from the transformer to the transfer switch, and then from the transfer switch to the electrical building, while also meeting the requirements of NEC 225.31: Disconnecting means.
Since the service disconnect is already located in the primary circuit of the transformer, I believe the transfer switch does not have to be "service entrance" rated, and so is not required to include a circuit breaker (for the utility power from the transformer).
The generator already includes a circuit breaker, that will protect the conductors from it to the transfer switch. These conductors have less current capacity than the conductors from the utility transformer.
My question then is if we install an incoming feeder circuit breaker in the electrical building (MCC), will this breaker protect both the incoming conductors from the transfer switch to the electrical building (MCC) and the conductors from the transformer to the transfer switch ? Does the fact the Transfer switch and transformer are approx 400' away affect code compliance for this ?
Or should we instead install a circuit breaker in the transfer switch (and not in the electrical building/MCC) to protect the conductors from the transformer to the transfer switch and from the transfer switch to the electrical building (MCC), which is 400' away. If we do it this way, will we need to install a disconnect switch in the electrical building (MCC) for the incoming feeder conductors ? or will the breaker in the transfer switch qualify as the disconnect switch for the feeders into the electrical building (MCC) under NEC 225.31 ?
Would appreciate any comments on this.