? on neutral size

[Husker apprentice]

Hey guys, Coming from a REA in Nebraska, All of our wye banks no matter what size it is, we use 3/0 copper back to system neutral. Alot of us lineman think its overkill but (that's the way it's been for the last 100 yrs. so its never changed). Also the primary neutral size is #4- 1/0 acsr. Any help or information would be helpful.

thanks

[dbrown20]

It should be derived from the fusing factor of your entity. If for example your co. uses the GE suggestion of 2.4 times the full load current then your neutral should be a little more that 2.4 times bigger in ampacity than the full load secondary current of that particular pot.

For example on a 25 KVA 120/240 pot the leads should be capable of carrying a tad more than 240 amps since the full load secondary of such a pot is approx. 100 amps.

If they're using 3/0 cu. on all pots, then yes, it would be overkill. Get out your transf. book and become familiar with the full load currents of most common pot sizes. Then ask someone what the fusing factor is for your company. Then you might understand.


Normally the neutral lead from each individual pot will be the same as the phase lead. This is only on a Wye secondary. Some companies use a smaller neutral lead on a delta hookup since on a 3 phase hookup the 3 phase will only use the phase wires and only the single phase imbalance will come back through the neutral. In this case the neutral doesn't need to be as big as the phase wires. In the delta I am talking about, I am referring to a combination bank that has both single phase and 3 phase load. dbrown20 Hi Bill.