More basic questions on wiring

[Grumps]

Probably basic to experienced installers, but I can't find the regs:

1) When using a lighting junction box in the loft, it must be screwed down. Where is acceptable? Top of joist (it'll overhang the sides), side of joist, or add a board across joists and secure to that?

2) When running T&E vertically in built-in cupboards, can they be left exposed or have they got to be covered? Circuits have RCD protection.

3) When wiring a double socket in a ring circuit, must you use both E connections?

4) When using 3-core&E for 2-way light switching for example hall/landing lights, does the E from the landing light switch go to the hall metal backbox, or is the hall backbox earthed by the T&E from the ground floor lighting circuit? Or do you use both E (maybe creating a loop?), or don't use the E in the 3-core&E at all as both landing and hall boxes will be earthed from the respective upper and lower lighting circuits anyway?

5) Is it better to notch a joist or drill a hole?

TVM

[Andy Burns]

fixed in any way is better than most I've seen laid on top if ceilings

can be exposed.

you don't have to, I think they're there to allow for high-integrity earthing on certain circuits.

I think all earths are considered equal after the main earthing terminal, I'd connect every E in a backbox to it.

[ARW]

1. You generally would not use JBs on a rewire. If you do have to use them make them accessible or use maintenance free. Fit them by the loft hatch screwed down if needs be.
2. Clipped direct is fine
3. No - unless requires by hi integrity rules or customer specs.
4. All cpc's must be earthed. Even if it creates a parallel circuit. So earth at both ends
5. Reuse what you have?

[Theo]

The reason it's called a CPC (circuit protective conductor) is that it's protecting the circuit, which includes the wiring. So it's not just about earthing the faceplate, but also the wiring run.

If you put a nail through the wire and connect line to CPC (earth), a current will flow and trip the RCD (or MCB if large enough). If you leave the CPC in a cable floating there won't be a trip, and the CPC wire will become live. That may cause surprises if somebody later comes along and connects some metalwork to it, expecting it to be earthed.

Theo

[John Rumm]

You generally need cable restraint, and having the box fixed as well as the cable clipped before entry, achieves that. So screwed down is much preferred. Anywhere you can get a decent fixing is good, but try and avoid places where it will be likely to get damaged.

If you are doing "loop in" wiring, there are unlikely to be many JBs anyway.

Surface is fine.

No. You can if it makes wiring easier / more logical with the selected cable entry points but there is not usually a requirement to unless the circuit in question is expected to carry high earth leakage currents.

All the earth wires in all the cables should be properly connected to earth.

Yes.

:-)

It depends on where along the span you are:

[Grumps]

Thanks all. And thanks for the links. "Under upper floors, cables can simply rest on the ceiling of the room below for support." So they don't need clipping at all, and I don't need to lift a whole floorboard length, run the cable, and clip it every 250mm?

[Owain Lastname]

No, if it's in a ceiling/floor void.

If it's in a loft it's better clipped as (a) it's neater (b) more risk of damage from feet or stuff being moved about.

Owain

[John Rumm]

To be fair that was written before the changes to the rules about fireproof fixings for cables. One could probably argue that in a domestic situation above plasterboard with 30 mins of fire protection, that is still ok, but a few non melting fixings here and there would not go amiss.

[Theo]

+1. While resting on the ceiling is ok by the letter of the law, by the time you're there you might as well do it tidily. Using metal fixings would improve fire safety and reduce the risk of things coming apart if you work nearby in future.

Although if it was an inaccessible void like a wall cavity I'd not insist on clipping.

The nice thing about DIY is you can do things above and beyond what a tradesperson who is up against the clock would do.

Theo