Lighting cable regulations

[daggermark]

Hi all, new around here, hoping somebody can help me with this question.

As I understand it, all cable concealed in a wall needs to tick one of these boxes:
- be buried more than 50mm
- have an earthed metal sheath
- be in earthed conduit
- be mechanically protected

In the event that none of these are ticked, the cable must be on an RCD. Please let me know if I'm wrong so far...

So onto my main question: If the above is true, then surely almost all lighting circuits should be on an RCD given that the light switch cable is normally buried in the wall but not compliant with any of the 4 points above?

The reason for my question is that my house lighting circuit is not protected by RCD.

Any help appreciated!

 

[JohnW2]

As I understand it, all cable concealed in a wall needs to tick one of these boxes: .... In the event that none of these are ticked, the cable must be on an RCD. Please let me know if I'm wrong so far...

Welsome to the forum.

You're just a little incomplete. If none of those boxes are ticked the cable must be RCD-protected and in one of the prescribed 'safe zones' - are you aware of that concept?

So onto my main question: If the above is true, then surely almost all lighting circuits should be on an RCD given that the light switch cable is normally buried in the wall but not compliant with any of the 4 points above?

Yes, that is true for any new wiring. Regulations are not retrospective, so there is not a requirement for RCD protection of existing wiring.

Hope that helps.

Kind Regards, John

 

[daggermark]

Thanks for your reply John, yes I'm aware of the safe zones also.

If modifying an existing lighting circuit (adding a second light for example), what would you say is the easiest way to comply? Use metal conduit and earth it somehow? Armoured cable? I believe most armoured cable is black/grey/brown, I assume the grey would need to sleeved with blue?

 

[JohnW2]

Thanks for your reply John, yes I'm aware of the safe zones also. If modifying an existing lighting circuit (adding a second light for example), what would you say is the easiest way to comply? ...

Depending on what you will be doing, you may find that there are varying opinions as to whether there is a need to comply. If you are installing any new buried cable, then you would certainly have to comply, but some would say that you don't need to comply if you've done nothing to buried cable (and have not installed new buried cable) but have merely modified, or added to, other parts of that circuit. What is your situation?

.... Use metal conduit and earth it somehow? Armoured cable? I believe most armoured cable is black/grey/brown, I assume the grey would need to sleeved with blue?

If compliance is necessary, installing RCD protection somehow would probably be the 'easiest' option! With armoured cable there would probably be a big problem terminating it and earthing the armour. If you used metal conduit, you would connect it mechanically to the metal back boxes, which in turn would be earthed (thereby earthing the conduit) - but that's really a job for a professional with the right kit.

Kind Regards, John

 

[Lectrician]

Adding RCD protection is likely the easiest way. However, if adding a light, not a switch, you could omit the RCD, as you only need to ensure your addition complies, not the whole circuit. This assumes no new cables buried in the wall.

 

[EFLImpudence]

As I understand it, all cable concealed in a wall needs to tick one of these boxes:
- be buried more than 50mm

Not exactly:
If concealed less than 50mm., they must be protected by an RCD.

That does not mean bury them more than 50mm. as, unless you have a castle, you will be contravening the Building Regulations by chasing deeper than one sixth the thickness of the leaf horizontally or one third vertically.

 

[daggermark]

Unfortunately the additional light is in the wall, meaning a new cable run which won't comply. Sounds like I'm getting somebody to add RCD.

 

[JohnW2]

Unfortunately the additional light is in the wall, meaning a new cable run which won't comply. Sounds like I'm getting somebody to add RCD.

Fair enough. As I and others have said, RCD protection of the circuit is almost certainly the easiest option. Depending on the overall situation, you might even want to consider having your whole CU upgraded to a modern one (with RCDs) thereby protecting most/all things in your house.

Kind Regards, John

 

[daggermark]

The CU does have RCD but only on the ring main, not on the lighting. There is actually a spare MCB on the RCD part of the CU, but I believe the lights are meant to be on a separate RCD? Or have I imagined this?

 

[Lectrician]

An RCBO can likely be added, and would be the best option.

 

[winston1]

The CU does have RCD but only on the ring main, not on the lighting. There is actually a spare MCB on the RCD part of the CU, but I believe the lights are meant to be on a separate RCD? Or have I imagined this?

There is no such requirement. But it makes sense to have more than one RCD.

 

[JohnD]

(with RCDs)

Or RCBOs

 

[JohnW2]

Or RCBOs

Indeed.

Kind Regards, John

 

[JohnW2]

.... but I believe the lights are meant to be on a separate RCD? Or have I imagined this?

People argue about this. There is certainly no regulation which explicitly requires that. There is, however a very vague regulation which requires an installation to be separated into circuits arranged so as to 'minimise inconvenience' in the case of a single fault. Some take that to mean that lights and sockets in a particular part of the house should not be on the same RCD - so that a single fault (or 'nuisance' RCD trip leaves every part fo the house with either lights or power..

Kind Regards, John

 

[SimonH2]

One option would be to move the lighting MCB to the RCD protected part of the board. There isn't really a problem (though it isn't ideal) having lighting and power on the same RCD - it's how just about all CUs are installed these days.