27 Jul 06 20:40
I am a long way from my copy of the NEC. I have the Canadian code, and it is reasonably close to the NEC. Anyone who is motivated may search the index of the NEC for a similar rule.
In North America, the neutral is virtually always the grounded circuit conductor.
Rule 14-016 states that:
Devices (Switches, breakers, fuses) shall not be connected in any grounded conductor EXCEPT WHERE;
(a) the devices simultaneously or previously disconnect all ungrounded conductors;
(b) an overcurrent device is in a two wire circuit having one wire grounded and there is a possibility that the grounded conductor may assume a voltage difference between itself and ground due to unreliable grounding conditions of sufficient magnitude to create a dangerous condition: or
(c) overcurrent devices are located in that part of a circuit that is connected by a two pole polarized or unpolarized attachment plug provided that the circuit is rated at 15A, 125 V or less.
Personally, I don't switch neutrals under any circumstances on three wire single phase circuits or the shared neutrals of three phase circuits.
I have seen too many problems and too much expensive and needless damage caused by failures or improper action of switches in neutrals.
I have never seen damage or encountered any problems caused be a solid (unswitched) neutral.
Another interesting point re the close similarity between the Canadian and American codes is in regards to voltage drop.
The NEC RECOMENDS that the voltage drop between the consumers service and the point of utilization not exceed 5%.
The Canadian code REQUIRES that the voltage drop between the consumers service and the point of utilization not exceed 5%.