480-240 / 240-120 single phase transformer

[dougjl]

I have a question concerning the secondary side wiring. There are 4 taps X1, X2, X3 & X4. I know to get 240 I tie X2 & X3 together and get 240 between X1 & X4. Is there a problem grounding X4 and having 240 with a neutral? This would be similar to a 120 type arrangement and would seem to provide a safer system since a ground fault would trip the feeder breaker. If I wanted 120V couldn't I just pull that off of the X2/3 junction and still use X4 as the neutral? I know that typically the arrangement is to ground X2 & X3 (not X4) which then give 120 between X1 to X2/3 and X4 to X2/3 and take 240 from X1 to X4. Can someone explain why that is? What am I missing?

Thanks,
Doug

 

[waross]

It depends where you live.
If you live in the UK the only issue is whether it should be X1 or X4 that is grounded. However there is no difference electrically.
In NEMA land, North America, the definition of the neutral is different, and the codes, both NEC and CEC state that if a conductor can be grounded in such a way that the maximum voltage to ground is 150 volts, it shall be grounded.
Also, if you are connecting loads to one leg and the neutral, X2-X3 in NEMA land, the neutral must be grounded.
Respectfully