Can a RCD be used as an Isolating Switch

[WhatNext]

Hi

In my house there are 2 MK consumer units.

Upper unit has an isolation switch and all the MCBs are for lighting circuits

Lower Unit has an RCD and all the MCBs are for ring circuits.

It was installed a while ago.

When I flipped the isolation switch in the upper unit I expected all the power to go off, however the lower unit remained on ??? ( Had a radio plugged in at the time )

I note that if you push the test button on the RCD the power trips which acts like an isolating switch, but you would have to know to do this.

What I was wondering should I call an electrician and have him fit another isolating switch fitted in the Lower Unit ?

Cheers.

 

[EFLImpudence]

Yes it's fine.

You can 'switch' them off as well.

 

[WhatNext]

Hi thanks

I was just worried that if someone flipped the isolation switch to off they might think the whole house was dead which is not the case !

 

[WhatNext]

Hi sorry me again.

When it comes to consumer units is it correct to say that you should always isolate each consumer unit individually and not assume that an isolating switch in one consumer unit would isolate everything assuming more than one unit in the same house ?

 

[Iggifer]

You should never assume an isolator has isolated everything no.

If you are concerned, you can always add a little label stating 'RCD not isolated by main switch' or worded however you want to do it.

You could use something like this

http://www.patlabelsonline.co.uk/el...pply-labels-for-multiple-power-supplies-p1141

but it's not really the correct label, it is however, the closest 'standard' one I can think of

 

[PrenticeBoyofDerry]

When I flipped the isolation switch in the upper unit I expected all the power to go off, however the lower unit remained on ??? ( Had a radio plugged in at the time )

You would not expect the isolator of one distribution board to isolate the circuit of another distribution board.

I note that if you push the test button on the RCD the power trips which acts like an isolating switch, but you would have to know to do this.

There should be a label on the board informing you that you have an RCD and the test button should be used quarterly, to assure the mechanics of the switch are functioning, this is a test button not an isolator. The RCD does have a dolly switch.

What I was wondering should I call an electrician and have him fit another isolating switch fitted in the Lower Unit ?

Is the RCD the main isolator of that board? If so there is no need for another form of isolator.
Apologise, I did mean that one isolator of a DB would not be expected to isolate another. Not sure what happened when I originally posted, hope I did not mislead. I blame the laptop!

 

[PrenticeBoyofDerry]

When it comes to consumer units is it correct to say that you should always isolate each consumer unit individually and not assume that an isolating switch in one consumer unit would isolate everything assuming more than one unit in the same house ?

When isolating, you should identify the circuit or circuits you are isolating and prove the circuits are dead, prior to any poking around.
When I isolate a board, I unload each circuit and isolate at a time, then throw the main switch.

 

[WhatNext]

Hi

Yes there is a note inside the second consumer unit highlighting that there is an RCD and it needs to be tested quarterly.

I take it that the dolly switch can be used as the isolating switch ?

Many thanks.

 

[PrenticeBoyofDerry]

I take it that the dolly switch can be used as the isolating switch ?

It can be, yes.

 

[ban-all-sheds]

You would NOT expect the isolator of one distribution board to isolate the circuit of another distribution board.

 

[ban-all-sheds]

Hi thanks

I was just worried that if someone flipped the isolation switch to off they might think the whole house was dead which is not the case !

That's why one should always follow the proper procedure to check.

One needs a proper 2-pole tester, not a volt-stick or neon screwdriver. Ideally not a multimeter, but if it's that or a magic wand then that will be much better.

Then basically:

1. Check that the tester works, either by using a known working supply or a proving unit.
   
2. Check that the circuit one wants to isolate is live.
   
3. Isolate it.
   
4. Check that it is dead.
   
5. Check that the tester still works, either by using a the same supply as at Step 1 or a proving unit.

Relying on labels is a bad idea, as people can, and do, change things - add new sockets supplied from lighting circuits, other floors, other CUs etc, and not update the labelling.

 

[JohnW2]

That's why you should always follow the proper procedure to check. You need a proper 2-pole tester, not a volt-stick or neon screwdriver. Ideally not a multimeter, but if it's that or a magic wand then that will be much better. Then basically: ...

Everything you say is very true, but the OP hasn't actually said that he necessarily intends to (now or ever) undertake any electrical work. He was merely concerned that someone who did undertake such work might be misled/confused by the fact that there were two CUs, with separate isolators. As you say, anyone who did work on the installation ought to know how to test to ensure that the circuit they were working on really was 'dead'.

Kinnd Regards, John

 

[WhatNext]

Hi

Yes that is correct. I was concerned that if someone assumed what I had initially assumed that the consumer units were interconnected the could get an electrical shock.

I am going to place a self adhesive warning label inside both consumer units so that it is obvious to anyone who opens them.

 

[plugwash]

Relying on labels is a bad idea, as people can, and do, change things - add new sockets supplied from lighting circuits, other floors, other CUs etc, and not update the labelling.

I would also note that while the "safe isolation" procedure is certainly good practice it cannot ever be an absoloute gaurantee that the circuit is dead and will stay dead.

For this reason there is a lot to be said for using insulated tools and avoiding touching conductors as much as possible even if you are not deliberately working live.

I also belive there is a lot to be said for neon screwdrivers as a last line of defense before touching a conductor but I know others disagree with me on that.

 

[JohnW2]

I would also note that while the "safe isolation" procedure is certainly good practice it cannot ever be an absoloute gaurantee that the circuit is dead and will stay dead. ... For this reason there is a lot to be said for using insulated tools and avoiding touching conductors as much as possible even if you are not deliberately working live.

Agreed.

I also belive there is a lot to be said for neon screwdrivers as a last line of defense before touching a conductor but I know others disagree with me on that.

I have to confess that I also agree with that - although, as you say, there will undoubtedly be some disagreement. However, if one has already done what everyone else would do in terms of 'testing for dead', I don't really see how anyone can really complain about one doing something in addition. The very worst scenario is that the 'additional something' will give 'false reassurance', but that's no worse than the position of the others - who presumably feel 'adequately reassured' without doing it at all!

Kind Regards, John