I'm trying to clear up an argument Ive been having with a contractor. We have a 4.16kV-480V D/wye transformer that is solidly grounded. From the transformer we only bring 3-wire + gnd over to a 480V MCC. The ground is connected to a ground bus in the MCC and used for all equipment grounds and grounding path. We do not bring the nuetral from the transformer over to a nuetral bus.
The Transformer is set up for a residual ground detection scheme and only used the three phase CT's and no transformer nuetral CT. Ground setting is 5A.
There is a piece of equipment fed from the 480V MCC which requires a nuetral. The contractors hooked the three phase wires to the breaker in the MCC and landed the nuetral on the ground bus in the MCC. I have told him that he cannot do this for this is a ground bus not a nuetral bus.
I informed him of the fact, that besides putting an intentional current on the ground system, they would also trip the breaker due to the residual grounding setup. If current went out on one phase and returned on the nuetral and then back to the transformer via the ground bus, the breaker would trip becasue it would not see this current returning on one of the residual CT's.
Am I explaining this correctly to him?
The Transformer is set up for a residual ground detection scheme and only used the three phase CT's and no transformer nuetral CT. Ground setting is 5A.
There is a piece of equipment fed from the 480V MCC which requires a nuetral. The contractors hooked the three phase wires to the breaker in the MCC and landed the nuetral on the ground bus in the MCC. I have told him that he cannot do this for this is a ground bus not a nuetral bus.
I informed him of the fact, that besides putting an intentional current on the ground system, they would also trip the breaker due to the residual grounding setup. If current went out on one phase and returned on the nuetral and then back to the transformer via the ground bus, the breaker would trip becasue it would not see this current returning on one of the residual CT's.
Am I explaining this correctly to him?
