I have a 480 VAC, 3 PH MCC with feeder cables of 3 parallel 500 MCM/phase. One of my buckets feeds a 45 KVA transformer; 480-208/120 vac, 3 PH. The primary feeders to the Xfr are 3-#4. The secondary cables are 3#4/0. The circuit breaker protecting the transformer is a 70A,3P breaker.
What's the size of the grounding conductor I need to run from the transformer's center tap?
Do you base the size on the feeder to the MCC? the feeder to the transformer? or the size of the secondary cables? Why?
What's the size of the grounding conductor I need to run from the transformer's center tap?
Do you base the size on the feeder to the MCC? the feeder to the transformer? or the size of the secondary cables? Why?