Switched neutral or not?

ktech · Mar 29, 2009

Can anyone point me to the part in the regs that explains when the neutral needs to be broken for isolation.

I'm looking in the case of a three phase sub board main incoming switch - when to use 3 and when to use 4 pole. And isolator switch for fixed appliance, again 3 phase - linked neutral or 4 pole switch.

I seem to remeber that if you have PME this has some effect due to the supplier not been able to guarantee the neutral is at earth potential?

johnnyb · Mar 29, 2009

Don,t know where you got that from mate, in my personal opinion i think its always better to use 4 pole, as the neutral being a phase conductor i think its better to break it on isolation.
Especially when its an appliance you know you are safe from any feed backs off somewhere else.

maddfridge · Mar 29, 2009

ktech said:
Can anyone point me to the part in the regs that explains when the neutral needs to be broken for isolation.

I'm looking in the case of a three phase sub board main incoming switch - when to use 3 and when to use 4 pole. And isolator switch for fixed appliance, again 3 phase - linked neutral or 4 pole switch.

I seem to remeber that if you have PME this has some effect due to the supplier not been able to guarantee the neutral is at earth potential?

hi there

look at 537.1.3 / 1.4 etc

after all neutral is a live conductor

cheers

Guest123 · Mar 29, 2009

maddfridge said:
hi there

look at 537.1.3 / 1.4 etc
after all neutral is a live conductor

cheers

I see what your saying, but 537.1.2 states that in a TN-S or TN-C-S system the neutral conductor need not be isolated or switched where it can be regarded as being reliably connected to earth by a suitably low impedance.

Big spanner in to vital works!!

P.S, just reading down the page it says the same thing again in 537.2.1.1 - neutral need not be isolated or switched in TN-S or TN-C-S.