Twin no earth in my lighting circuit

[levstar]

Hi wondered if I can clarify something...

I have just bought a light fitting which is metal, when I came to install this in my bedroom I find I have on Twin cable, no earth.

After clambering around in my loft I find that not only do all my lighting cable run under insulation and boards there is no easy way of pulling through my feed to the upstairs circuit from the consumer unit, not with out causing massive disruption to the rest of the house.

So after some consideration I wondered if the below plan would be a sensible and compliant way forward:

Leave the existing 1mm twin cable feed from the consumer unit.

Rewire the whole of the loft lighting circuit in new 1mm T+E cable running and clipping the cable on the roof beams.

Pick up an earth using 1.5mm single core earth cable from a socket in airing cupboard, bootlacing this to the main earth cable on the socket and running it to my lighting circuit.

Please advise.

Cheers

 

[Taylortwocities]

Your choices are
1. rewire the lighting circuit(s) with twin and earth (note this will be notifiable work and you will need to add an RCD for the lighting circuits created)
2. Take the light fitting back and get a double insulated (class II) one.
3. Take the light fitting back and install plastic ones.

There is some very relavent information here
http://esc.org.uk/pdfs/business-and-community/electrical-industry/BPG1v2_web.pdf

This relates to a CU change but the infoo on the light fittings is "a point" as they say in frogland.


Note, for 2 & 3, you should also remove any other metal light fittings and switches as they will not be earthed..

 

[flameport]

No. Not sensible or compliant.

 

[wingcoax]

To start with, what type of cable is in place? is it grey oval or what?
Secondly, what you propose would not be allowed under the regs(the circuit would have to originate at the CU along with the earth. Also, before anyone else says, this would come under "PART P" of building regs.

 

[Risteard]

you will need to add an RCD for the lighting circuits created

Depends on how it is installed.

 

[Taylortwocities]

Depends on how it is installed.

Yes, he could rewire the lighting circuit and put all of the lighting drops in surface conduit. But please, why do you throw in curved balls like this into a DIY forum.

If you want to discuss minutii of BS7671, why dont you go play on the IET forum? They'll love you there.

 

[levstar]

Ok, As I want to add other metal swithces etc, I will bite the bullet and replace the twin cable with twin and earth.

However not sure why this would need to be rcd protected?

The old cable in 1mm grey flat cable parts of it have black conduit at the top where entering the walls for the switches, the strands of the wire are silver, possibly tinned copper or aluminum?

 

[Risteard]

Yes, he could rewire the lighting circuit and put all of the lighting drops in surface conduit. But please, why do you throw in curved balls like this into a DIY forum.

Or just bury it deeper than 50mm.

And I do also use the IEE forum thanks.

 

[333rocky333]

However not sure why this would need to be rcd protected?

Theres a reg regarding cables buried in walls less than 50mm deep needing RCD protection.
The wires down to your switches are likely to be less than 50mm deep.

 

[levstar]

Thanks however if the cable run from the CU run up the corner of the wall to the loft space and the cable runs ran vertically down to the light switches I was under the impression that no rcd or mechanical protection is required?

 

[333rocky333]

They are safe zones, where cables may be less than 50mm buried.
Outside those zones cables must be buried over 50mm
Seperate issue to the Rcd requirement which is for both areas.

 

[333rocky333]

reg 522.6.7 if you have the book

 

[AndyPRK]

Seperate earth cable needs to be a minimum size for mechanical robustness. 4mm I think ?

 

[Risteard]

Seperate earth cable needs to be a minimum size for mechanical robustness. 4mm I think ?

4mm if not mechanically protected.

 

[levstar]

Hi Thanks for the all the advise, in the cold light of day I think this job is becomming mamouth I am now thinking:

The separate earth is a bad idea.
I will revert to plastic fitting and double insulated lights.

However still not clear on a couple of things:
1.If I leave the twin (with no earth) in place if I ever want to add a light or switch can I do this using twin and earth if so what happens to the earth wire, should this be removed or taped in someway to prevent mis use.

2. Also re the RCD having read the regs still not clear why an RCD would be needed if installed in a safe zone.

3. Also I have a split board where my lights are on an MCB and the sockets are on an RCD for fail over purposes I guess. What should I do can I install an RCBO even though the circuit has no earth?

Thanks once again