rcd for lighting circuits

[wellerman]

Refitting bathroom on a late 50's property that I have recently moved into. I understand the need to have an RCD protected lighting circuit, however my current install which has a modern CU seems to have retained the old metal conduit for the lighting circuit up and downstairs, and is currently wired to the main switch side of the CU and therefore not RCD protected.

Difficult to see whether all the wiring was replaced when the CU was fitted, but it probably wasn't! All light fittings still have the circular steel mounting boxes sunk into the walls. The ring main is T&E but sheathed in the old solid green not green/yellow.

As I am laying a new tiled bathroom floor I will not be taking it up in the future if a re-wire is necessary. I was thinking I could lay the wire in preparation for connection at a later date, and placing any junction boxes outside of the bathroom (i.e. under the landing floorboards or the adjacent bedroom). The rest of the house is to be decorated anyway so I can put new switch boxes in place /run next to existing ones.

There are two spare slots on the 30mA RCD part of the CU which I can use for lights up and lights down.

Until the new wiring is in place and connected is it acceptable to move the current lighting from the Main side of the CU to the RCD side whilst maintaining the current earthing on the conduit?

Or should I just cross-bond in the bathroom as an interim measure until all the wiring is complete?

 

[ericmark]

It is hard to give advice without seeing exactly what you have. But how about conduit with draw string in. Especially if straight run.

 

[too old to learn]

hi wellerman.
if it was me I would do as you sort of suggest.
switch the lighting to the RCD side of the CU (if you have experience of this, remember electric ain't your fried and will quite easily make you meet your maker). this removes the requirement for supp bonding.

you need to think though what ever is under your bathroom (kitchen / living room?) will need rewiring at some point, so you need to take into account of all sockets / lights / aerials? etc that will need to be installed. this is where it will be extremely difficult!

Personally, if is your plans to have it rewired in a short period of time (year or two) I would not lay the tiling down. sods law says that you will need to lift it up again!

oh and remember, all junction boxed need to be easily accessed for testing, therefore can not be hidden under floor boards etc

 

[ban-all-sheds]

Refitting bathroom on a late 50's property that I have recently moved into. I understand the need to have an RCD protected lighting circuit, however my current install which has a modern CU seems to have retained the old metal conduit for the lighting circuit up and downstairs, and is currently wired to the main switch side of the CU and therefore not RCD protected.

Is the conduit just a containment system, or is it also used for the circuit earth? What sort of cable is in it?

And in any event, the fact that it's in conduit doesn't mean it can't be on an RCD.

Difficult to see whether all the wiring was replaced when the CU was fitted, but it probably wasn't!

A PIR would probably be advisable.

All light fittings still have the circular steel mounting boxes sunk into the walls. The ring main is T&E but sheathed in the old solid green not green/yellow.

What sort of T/E? Solid copper core or stranded tinned? PVC or rubber?

In the late 50s they were still using rubber cables, and these are well past their use-by date.

A PIR would definitely be advisable.

As I am laying a new tiled bathroom floor I will not be taking it up in the future if a re-wire is necessary.

I'm afraid you will, whether you want to or not, unless removing the ceiling in the room below is an option.

Wiring lives under whatever you put on the floors, above whatever you put on the ceilings, and beneath whatever you put on the walls.

You have just moved into a property which could well have wiring over 50 years old and you are refurbishing it. It is lunacy not to sort the electrics out before you do anything to the floors/ceilings/walls.

I was thinking I could lay the wire in preparation for connection at a later date, and placing any junction boxes outside of the bathroom (i.e. under the landing floorboards or the adjacent bedroom).

No. Who do you think is going to come along later and use cables you've left lying there? Do you know about the rules for junction boxes?

Are you aware of this: //www.diynot.com/wiki/electrics:part-p?

The rest of the house is to be decorated anyway so I can put new switch boxes in place /run next to existing ones.

Get the whole place inspected now, and get any electrical work done before you pick up a paintbrush or a roll of wallpaper.

Until the new wiring is in place and connected is it acceptable to move the current lighting from the Main side of the CU to the RCD side whilst maintaining the current earthing on the conduit?

Do you have the necessary equipment to test for insulation resistance and continuity of the earthing?

Or should I just cross-bond in the bathroom as an interim measure until all the wiring is complete?

No, you should get an electrician to carry out a PIR now, and get any electrical work done before you do anything else.

 

[1john]

Dont put your lights on the RCD side, you would end up in complete darkness if that RCD tripped, and im assuming it is feeding all the sockets, so odd's on it will trip.

 

[electronicsuk]

Dont put your lights on the RCD side, you would end up in complete darkness if that RCD tripped, and im assuming it is feeding all the sockets, so odd's on it will trip.

Sadly that's not an option for the bathroom - all circuits entering it must be RCD protected, lighting or otherwise. It's not particularly feasible elsewhere in a modern house under the 17th edition either, as there will be wiring buried at <50mm deep without mechanical or earthed metallic protection.

This may not be so in the OP's due to the steel conduit that's already in place, but that's irrelevant to the bathroom.

 

[GaryMo]

Maybe it was 'don't used the RCD side but instead use an RCBO on the non-RCD side as it's a modern CU'.

I normally read too much into things though!

 

[1john]

the circuits in the bathroom dont have to be on the same RCD.

this guy could have an electrician put RCBO's on his lighting circuits.

to the OP, get a periodic report done before you do any work, you should get the bones of the house sorted before you make it pretty, it saves so much greif in the future.

 

[wellerman]

Thanks all.

I'll get a PIR and go from there.

 

[1john]

Thanks all.

I'll get a PIR and go from there.

good man, it's the best way to go !

 

[ban-all-sheds]

Come back and let us know what it says?