Can I install double pole MCBs instead of double pole switches for a water heater?

[Andy™]

then do as others have suggested and fit a key type switch so you still have local isolation but cant be turned on / off easily by people in the room

 

[Luderic]

Well yes I could do that, but I would prefer avoiding it. Since the guests won't be able to use it because they won't have the key, what's the point of even having one inside the bedrooms (apart from what you said earlier being able to make sure that nobody switches it on while it's being repaired, but providing this may happen only every 5 years or so, I might as well find another solution  - like a padlock on the DB!).
And I find it much more convenient to be able to switch it off - if needed - from outside the bedrooms, rather than having to walk into the room.

 

[Andy™]

fit a local isolation point next to the appliance, then have whatever fancy controls you want elsewhere. there you go, no need to go into the room to turn it on/off, but there is a nice handy isolation point for anyone working on it

 

[Luderic]

Excellent idea! Best of the two worlds actually! Thank you.

 

[Rob_the_rich]

What do the Manufacturer's Instructions say? Link possibly? I assume they specify DP isolation.

 

[Luderic]

It's not related to the manufacturer, but to the country. In England one must install a double pole switch, unlike in other European countries. I'm based in Malta, where they use the same regulations as in the UK, so I have to install double pole switches.

 

[Andy™]

7671 says manufacturers instructions are to be followed, so if they say local DP switch is required then to fit fit one means you havent fully complied with 7671

 

[Rob_the_rich]

In England one must install a double pole switch

As far as I can see it, a DP switch, as opposed to a SP switch, is only required for

1. water heaters having immersed and uninsulated elements (554.3.3)

2. where MIs specify them (134.1.1) or

3. installations other than TN-C-S or TNS (537.1.2) due to the neutral being reliably connected to earth

 

[Evans Electric]

We are supposed to work to the Regs  as in BS7671    which ask for a local isolator .  Whether its SP...DP or TPN   is irrelevant.    This is because not everyone is an electrician ,  so a plumber say,  doing work to the heater needs to isolate it ....he doesn't know where the fuseboards are ...they may not  have the circuits labeled up .    A breaker /fuse in a board   somewhere in the building is NOT a local isolator  I'm afraid , however much you want it to be ..the operative word is ...LOCAL.  

 

[Doc Hudson]

7671 says manufacturers instructions are to be followed, so if they say local DP switch is required then to fit fit one means you havent fully complied with 7671

They used to say that, but not any more. They currently say "The installation of electrical equipment shall take account of manufactures instructions". Which leaves an element of individual interpretation without any compliance or non compliance issues.

Doc H.

We are supposed to work to the Regs  as in BS7671    which ask for a local isolator .  Whether its SP...DP or TPN   is irrelevant.    This is because not everyone is an electrician ,  so a plumber say,  doing work to the heater needs to isolate it ....he doesn't know where the fuseboards are ...they may not  have the circuits labeled up .    A breaker /fuse in a board   somewhere in the building is NOT a local isolator  I'm afraid , however much you want it to be ..the operative word is ...LOCAL.  

There are regulations that refer to remote isolation, 537.1(i),   537.2.1.5, so you cannot say that BS7617 specifically asks for local isolation. A lot of manufactures instructions request it. but as BS7671 no longer states that they should be installed in accordance with manufactures instructions.

I think there is some confusion slipping in here in relation to effective means of isolation for ready operation for circuits and equipment as may be necessary to remove danger. Which relates more to industrial machinery, emergency stops, motorised equipment etc. In 132.15, which in reality is not a significant danger in relation to the OP's application. It is a fact that BS7671 does permit some remote isolation. Personally I would prefer stuff to be kept local wherever it is practicable. But I can see that in certain situations remote wired isolation device may be a preferred option. Any competent person working on these circuits is not going to be endangered by some MCB locks and clear labeling.

Doc H.   

 

[Evans Electric]

Ah  OK   there you go then Luderic , do it however you like .

No need to switch the neutral anymore  according to  537.3.2.5 .

537.3.2.4  does say  the isolator should be "convenient"  .  Make of that what you will .  

They change these things so often  now  its hard to keep up . 

 

[Luderic]

LOL. Well, the least I can say is that it's not very clear.

Anyway, I think I'll do what Andy suggested. I'll install a double pole switch near the water heater out of reach of the guests (probably in the false ceiling) so that anybody working on it can fully isolate the heater. I'll leave it on all time and install the remote control inside the DB.

Thank you everyone for your brilliant suggestions/contributions.