Double pole switch a must for storage water heater?

[Statick]

From a regulations standpoint, is it a must to use a double pole switch for storage water heater? I don't seem to find it worded as such in the BS standards. The reason I am asking is I want to replace my current double pole switch with a run back timer from CP Electronics. This run back timer seems to have the neutral connected together and looks like it's not a double pole by definition.
Thanks for your help.

 

[telectrix]

in the past, thousands of immersion heaters were installed with a FCU that only isolated L. i can't see a problem except that a falied element could trip RCD with just the N still connected.

 

[davesparks]

You should fit the time controls after the means of isolation as the time control will almost certainly not be suitable for use as a means of isolation.


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[dean.diy]

Lock off the MCB to the dedicated circuit?

 

[telectrix]

think davesparks gave the best solution. fit the timer after the D/P switch.

 

[Statick]

in the past, thousands of immersion heaters were installed with a FCU that only isolated L. i can't see a problem except that a falied element could trip RCD with just the N still connected.

Yes, and I am wondering from a regulations standpoint, is single pole still allowed for immersion heaters?

 

[Statick]

You should fit the time controls after the means of isolation as the time control will almost certainly not be suitable for use as a means of isolation.


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Interesting idea. Never thought of that. That would be one way to ensure to meet regs.

 

[Statick]

think davesparks gave the best solution. fit the timer after the D/P switch.

I agree. One thing that just came across my mind is that with this arrangement, it is likely that the D/P switch would be left permanently in the ON position.

 

[telectrix]

I agree. One thing that just came across my mind is that with this arrangement, it is likely that the D/P switch would be left permanently in the ON position.

it needs to be to maintain power to the timer . the switch will be for isolation only, while the timer controls whether the heater is on or off.

 

[westward10]

Single pole isolation is fine for a TN system where neutral is deemed at earth potential. Double pole would be required for a TT system.

 

[davesparks]

Interesting idea. Never thought of that. That would be one way to ensure to meet regs.

Why not? It's the standard way of doing it.

 

[davesparks]

Single pole isolation is fine for a TN system where neutral is deemed at earth potential. Double pole would be required for a TT system.

Technically correct, but in practicality you don't get many 20A SP switches with the required contact gap for isolation.

 

[westward10]

You are correct I doubt you would find many, but the original query asked if single pole isolation is acceptable and it is so long as the earthing system is not TT.