I have an existing building with a double ended switchboard with each end fed from a different transformer. The owner would like to have a portable generator back up one end of the MSB. In order to do this the transfer switch's normal feed will be from the secondary of the transformer feeding that end. My design calls for a new 4000A transfer switch w/ a 4000A circuit breaker on the normal side of the transfer switch in order to protect the transfer switch and thus the neutral/ground bond existing in the MSB will need to be disconnected and bonded at the transfer switch since this is now the first OCPD/disconnect for the service into this building. The new GEC at the transfer switch will be extended into the building to the grounding bar in the MSB. The owner's engineer reviewing the plans does not want to move the bond and feels the 4000A circuit breaker is not required at the transfer switch. Any thoughts????
ocpd for transfer switch
- Thread starter bwyllie
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ron
Senior Member
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- New York, 40.7514,-73.9925
Re: ocpd for transfer switch
How long is the conductors from the xfmr secondary to the existing main circuit breaker for that service? Is the xfmr utility owned? Where is the meter/ct's relative to the xfmr (primary or secondary). Are you sure that the existing n-g bond occurs at the breaker for each xfmr secondary?
How long is the conductors from the xfmr secondary to the existing main circuit breaker for that service? Is the xfmr utility owned? Where is the meter/ct's relative to the xfmr (primary or secondary). Are you sure that the existing n-g bond occurs at the breaker for each xfmr secondary?
ron
Senior Member
- Location
- New York, 40.7514,-73.9925
Re: ocpd for transfer switch
OK agree with you. Add new 4000A breaker on the upstream side of the normal termination of the xfer switch. The new breaker will have to be service entry rated. n-g bond would occur at the new breaker or at the new location of the meter. I guess you will also move the utility metering to the line side of new breaker too.
I have heard of service entry rated xfer switches that include a disconnect if your interested.
OK agree with you. Add new 4000A breaker on the upstream side of the normal termination of the xfer switch. The new breaker will have to be service entry rated. n-g bond would occur at the new breaker or at the new location of the meter. I guess you will also move the utility metering to the line side of new breaker too.
I have heard of service entry rated xfer switches that include a disconnect if your interested.
Re: ocpd for transfer switch
Would it be possible to modify the bus in the MSB? Intercept it after the MCB, run it to the ATS and then back to feed the MSB? This would save the cost of a new breaker. You wouldn?t have to mess with the GFP system or utility metering either. Buss duct would be an ideal wiring method in this case.
Would it be possible to modify the bus in the MSB? Intercept it after the MCB, run it to the ATS and then back to feed the MSB? This would save the cost of a new breaker. You wouldn?t have to mess with the GFP system or utility metering either. Buss duct would be an ideal wiring method in this case.
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