thetucsonkid
New member
I have a question about NEC requirements for grounding circuits fed through a transfer switch from either normal building power or generator backup power.
I am in the process of replacing several old transfer switches that feed MCC's with split busses. The split bus provides power to some of our critical equipment. We do very hazardous manned testing so the equipment is life critical. When the transfer switches were installed in the 60's they ran 3 wires from the generator to the transfer switch, but no ground from the generator. The loads are grounded using the normal power feed ground.
My contractor is now telling me that they need to run grounds from the generator as well. Since this is a very long run, approximately 1500 ft. the cost will be significant. They are quoting NEC 250.4 (5) as justification. My problem is that I don't see what this second ground will do. The transfer switches don't switch the ground. The generator is a 480 vac delta, permanent installation.
Any insight or advice will be greatly appreciated.
I am in the process of replacing several old transfer switches that feed MCC's with split busses. The split bus provides power to some of our critical equipment. We do very hazardous manned testing so the equipment is life critical. When the transfer switches were installed in the 60's they ran 3 wires from the generator to the transfer switch, but no ground from the generator. The loads are grounded using the normal power feed ground.
My contractor is now telling me that they need to run grounds from the generator as well. Since this is a very long run, approximately 1500 ft. the cost will be significant. They are quoting NEC 250.4 (5) as justification. My problem is that I don't see what this second ground will do. The transfer switches don't switch the ground. The generator is a 480 vac delta, permanent installation.
Any insight or advice will be greatly appreciated.