Consumer Units with RCBOs

[ARW]

A length of steel conduit with the ends made off properly is also fine.

[Tricky Dicky]

Even if it is buried below the plaster?

Richard

[ARW]

Yes.

[Fredxx]

I thought protection had to be more than 3mm of steel and steel conduit is only 1.6mm

When you say the ends are made properly, do you mean the conduit is earthed?

[ARW]

There is actually no specification for the thickness of the steel other than "3mm is deemed to be adequate".

1.6mm earthed steel conduit will pass.

The NICEIC seem happy for you to just use steel conduit (as long as you are paying them your subs).

I have always found it easy enough to sink the cables 50mm deep.

[PeterC]

I considered chasing in some runs, just for neatness*, but how the hell do you get 50mm from both sides of a 100mm wall? The cable would always be a bit off-centre and it's more than 0mm thick. Where the cables are in the wall (historic routes) they're steel capped but only the thin steel - just enough for a bit of a warning - and open at the back. The internal walls are also hollow block - too much cutting...!

*I actually prefer surface trunking - I like to be able to get at cables and pipes.

[dennis]

Capping is only there to protect it from the plasterer. It can be plastic.

[Mike Clarke]

The metal capping is very soft.

Believe me, if you hammer the pin for a picture hook into the wall and it goes through a bit of metal capping you will be totally unaware of it

- until the pin hits the line conductor.

As others have said the capping is only for temporary protection against plasterers.

[PeterC]

Yes, a hook's pin will go through it (don't ask...). This house was last plastered in about 1950. There's not sufficient wall to get conduit in as it would break into the hollow.

[tabbypurr]

That's easy. Chase 2" deep, fit cable. Go to other side, chase, adjust position to ensure it's the full 50mm deep :) Plaster, or should it perchance prove necessary, rebuild wall.

NT :)

[ARW]

Generally on the 17th and 18th edition regs then you would use RCD protection. This was a specific case for Richards man caves to provide discrimination.

But yes, good point, I never asked how deep his wall was.

[Tricky Dicky]

The wall where the garage supply cable will be buried in the wall is an exterior cavity wall with the internal wall being cinder type breeze blocks so quite easy to chase out to a depth of 50mm. Elsewhere the cable will run either through trunking or on the surface. I am a little concerned about carving halfway through the blocks for a 2m vertical run and I am not sure if they are already the hollow type, the ones I have had to sink boxes into elsewhere appear solid but you never know?

Richard

[ARW]

It's 50mm from final finished surface not 50 mm into the blocks.

[PeterC]

Just to clarify: if the cable(s) are protected by a 30mA, 30ms RCD or RCBO do they have to be a) protected b)as far in a 50mm? It seems that surface-mounted mini-trunking would be OK; what if that were flush with or just below the surface?

[tabbypurr]

no, those are alternatives to RCD, at least as far as cable protection is concerned.

yes

then it needs RCD to mitigate against the risk of drilling into it.

NT

[ARW]

If the cables are less than 50mm from the final finished surface then

30mA RCD protection is required. They need no further protection other than to be run in the required zones.

ie

The 18th edition now requires RCD protection of domestic lighting no matter what cable or installation methods you use.

[John Rumm]

The RCD protection alone is adequate. Its only when RCD protection is not available, that other remedies may become required.

For a non RCD cable, then its needs:

Surface wired (bare or in trunking), or To be buried >= 50mm from the surface, or Mechanically protected by earthed metal - be it capping, conduit, armour etc, or A deviation from the regs based on the specific circumstances.

If its visible and obviously a cable, then its fine.

[stephenten]

Adam, I have been following this thread with interest as I have a similar situation as the OP.

I have a house consumer unit in the hallway. A cable runs in a straight line from the middle of the back of the consumer unit straight through a double skin wall, then a ceiling - floor void and then a second double skin wall and then it is surface clipped around the garage wall to a secondary consumer unit which will be filled with RCBOs. So from my understanding of this thread I can fit a 45a MCB in the main consumer unit and connect the secondary consumer unit to that?

The cable is currently 6mm2 T&E and is more than 50mm from the floorboards and plasterboard......

[stephenten]

If all else fails I think I could use the 6mm2 T&E as a draw wire to pull through some 10mm2 SWA cable but I then need to think about being able to open up the existing holes without damaging other cables that share the same holes....

[PeterC]

Thanks for this. Unfortunately, some of my cables aren't in Safe Zones and I can't go to

50mm, so they'll have to stay on the surface. ATM the lights are on a 100mA RCD, but I intend to replace the MCBs with 30mA, miniature, RCBOs.