question re neutral sizing, 1 phase load from three phase supply

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BrianMuir

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Comox BC
Hi, I'd just like to confirm if I have this right

I have a three phase 120/208 supply & want to connect a new load, all single phase (ie 3 wire), consisting of about 25KVA at 208 (heat pump, hot water tank), and an assortment of other loads at 120V totaling 8KVA. (basic lighting and receptacle loads)

Assuming the 8KVA are evenly spread between Phase A and Phase B, then it seems to me that the worst case unbalanced load is 4KVA (when only one phase set of 120V loads are on) and this is what the neutral could be sized against.

Now, I do not intend to cut back the neutral ampacity this severely, but it sure seems fiscally prudent to shave it back a couple of sizes compared to the phase lines, especially considering I am looking at long runs.

Note that I am working against the CEC which requires the neutral ampacity sized to the unbalanced load. From what I can tell the NEC is similar.

As always, I certainly appreciate your kind support.
 
The nec wll allow us to size the grounded conductor for a feeder as small as the egc. That is, of course, if the calculated load is that small. For a service we can size to the minimum which would be the GEC.
 
yes, turns out I have a similar rule... neutral cannot be reduced further than required min size of bonding conductor, which makes total sense.
 
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