Engineering Notes 052
August 19, 1994
Due to recent National Electric Code changes, customers have started running double neutral feeders to their touring racks. Previously on single neutral feeders, some customers had been bundling all five wires at their shop to make it easier to run the feed on the road.
With the addition of the added sixth wire, this bundle gets very large. Some customers have attempted to solve this into two bundles with the three phase wires in one bundle and the two neutrals and ground in the other. This unfortunately is not a good practice. When all the wires in the feeder are bundled together, the magnetic flux generated from the currents in the neutral wire is canceled by flux from the phase wires. When you separate the neutral and grounds in one bundle, there is nothing to cancel the flux from the neutral wire. This causes current to be induced on to ground wire running in parallel with it on a 100 foot run to a 400 Amp service, we have seen ground currents as high as 50 Amps. Also, any other wires from around the stage that are running in parallel with either the neutral or phase fees may pick up current also.
The solution to this is to keep your neutral wires neutral your phase wires and run your ground wire separated from the phase wires. For those who run single feeder wires, this rule still applies.