Isolation switches

[pred]

Am I correct in the assumption that the purpose of the isolation switch is so that the appliance can be turned off before you touch it?

If this is true, if it is possible to unplug the appliance without touching it, is that not acceptable?

Many thanks.

 

[PrenticeBoyofDerry]

Isolation is intended to cut off the power supply for safety reasons, what ever that reason maybe, not just touching things.
But a plug could be considered a means of isolation. Provision would be that it is suitable to disconnect when on-load.

 

[Johnmelad]

Though you might not want to pull on this!

 

[bernardgreen]

Isolation switches do not (normally) isolate the CPC ( earth ) from the appliance. Unplugging an appliance will remove the CPC and there may be situations where the isolated appliance should still be earthed.

 

[ban-all-sheds]

Blimey - we had better ban plugs and sockets straight away then, if it might be dangerous to ever have an appliance unplugged.

 

[JohnW2]

Unplugging an appliance will remove the CPC and there may be situations where the isolated appliance should still be earthed.

As BAS has said, that is an extreme view which would have very widespread and ridiculous implications. Do I take it that the 'situations' you have in mind invove the absence, or loss, of required main bonding - or were you thinking of something else?

Kind Regards, John

 

[bernardgreen]

I was using "appliance" in its widest use and would include.

Isolating an outside lamp. One could argue that if Live and Neutral are isolated then the lamp does not need a CPC during the period of isolation.


A rack of electronic equipment with connections to the world outside the equipotential zone.

A lighting controller that feeds several lights around the house. Where this system uses 2 or 5 amp sockets for the lights then a permanent CPC is required at each socket and any metal and not double insultated light fittings will require a permanent CPC.

 

[JohnW2]

I was using "appliance" in its widest use and would include. Isolating an outside lamp. One could argue that if Live and Neutral are isolated then the lamp does not need a CPC during the period of isolation.

I would certainly argue that, wouldn't you? Why should an outdoor 'object' not connected to L and N of an electrical supply require a 'CPC'? Once the L and N are isolated, it surely is no different from any other conductive outdoor object, is it?

A rack of electronic equipment with connections to the world outside the equipotential zone.

Yes, that's one possible case. Any extraneous conductive parts of such connections obviously should be bonded, but even BS7671 acknowledges that this will not always be possible.

A lighting controller that feeds several lights around the house. Where this system uses 2 or 5 amp sockets for the lights then a permanent CPC is required at each socket and any metal and not double insultated light fittings will require a permanent CPC.

I'm not sure what you're getting at here. Are you talking about a plug-in controller feeding all the 2/5A sockets?? If so, if it were unplugged, then there surely would not be any need for a CPC at the sockets whilst it was unplugged?

In any event, if there are a few situations (like the comms equipment) where a permanent CPC is desirable, then one clearly should not connect it via a plug/socket.

Kind Regards, John

 

[ericmark]

Table 53.2 - Guidance on the selection of protective, isolation and switching devices gives a list of what is suitable for what.

There are three functions:-
Isolation
Emergency Switching
Functional Switching

Plug and socket-outlet is allowed for Isolation and Functional Switching but not Emergency Switching.

It also states (3) Device is suitable for on-load isolation, i.e. disconnection whilst carrying load current.

As sockets increase in size they also exceed the size of hole permitted to stop anything entering the hole. So over 32A it needs an isolator anyway.

 

[JohnW2]

Table 53.2 - Guidance on the selection of protective, isolation and switching devices gives a list of what is suitable for what. There are three functions:-
Isolation ... Emergency Switching ... Functional Switching
Plug and socket-outlet is allowed for Isolation and Functional Switching but not Emergency Switching. ... It also states (3) Device is suitable for on-load isolation, i.e. disconnection whilst carrying load current.

That's all true (except that it's actually Table 53.4 in BGB). Everything with a 'yes' in the 'Isolation' column, other than fuses, also has that 'note 3' indicating that it is suitable for on-load disconnection.

As sockets increase in size they also exceed the size of hole permitted to stop anything entering the hole. So over 32A it needs an isolator anyway.

Interestingly, the Table indicates that both plugs/sockets ≤32A and plugs/sockets >32A are suitable for 'Isolation', but that only the former are suitable for 'Functional Switching' (neither being suitable for 'Emergency Switching').

Kind Regards, John

 

[pred]

I assume you lot know what you're talking about, you're way over my head now, the reason I asked was I'm renovating a 1930's to rent out, and although I'm doing the chasing out and assisting with the 1st fix I know my limitations and it needs to be signed off or whatever, something akin to the landlords gas safety check I believe, anyway, my limited know how, I know the appliances must be able to isolate without touching the washing machine or whatever, and I thought what if I positioned the socket to one side so as to be able to switch off or does that contravene regs.

 

[JohnW2]

.. anyway, my limited know how, I know the appliances must be able to isolate without touching the washing machine or whatever, ....

To the best of my knowledge, there's no regulation which says quite that.

... and I thought what if I positioned the socket to one side so as to be able to switch off or does that contravene regs.

Nearly all washing machines are just plugged into sockets (often, probably usually, with no other local means of isolation), and many of those sockets are essentially inaccessible behind the machines! An accessible plug/socket would therefore be 'better' than very many people have.

Kind Regards, John

 

[RF Lighting]

It needs to be readily accessible to disconnect the appliance for maintenence or in case of emergency.

Tucked away in a cupboard behing a load of tins of food etc, isn't really very good.

If the appliance is free standing, and the socket is on the wall next to the appliance, I don't really see a problem with that.

You could always install a grid switch above the worktop, and just have one nice neat switch to control all the appliances.

 

[ericmark]

I don't think you have to have a means of isolation but having seen what happens when a weight becomes lose I would always fit one myself.

New washers well at least mine has an auto switch off should it shake too much but you will not know if a new or old washing machine.

 

[bernardgreen]

having seen what happens when a weight becomes lose I would always fit one myself

or a tumble drier when the OFF switch failed to turn the appliance off.