rewiring a light circuit

[John Rumm]

Dunno, I keep him well filtered ;-)

[Vir Campestris]

So there's no danger to the 2.5mm cable as the socket will burst into flames first?

Though I suppose that's equally true of any double socket anywhere on the ring.

Incidentally I've installed sockets (pre-part P honest!) and noticed the limit. I'll give odds most people have no idea.

Andy

[John Rumm]

In many cases there will be no danger to the cable at all (since it will often have a greater installed capacity than the 26A theoretical load of the socket. Even if if you do exceed that, then the cable does not immediately fail - it just runs over the 70 degree temperature limit that allows the cable a virtually unlimited life. If you routinely overheat it, it will have a shorter life before the insulation becomes brittle and starts to crack etc.

There is perhaps more risk to the socket, but again it does not seem to be a problem in real life since its not actually that easy to get 26A (i.e. over 6kW) of load on a socket for a long duration. Most people would probably shy of doing it too often once they realise that it would get 'kin hot running at max capacity for an extended period.

Indeed. Some good quality sockets will carry more current indefinitely anyway, the 20A is the notional design current.

Part P does not prevent you installing sockets anyway... ;-)

[tabbypurr]

It's hard to come up with a realistic scenario where a double socket would supply 26A for long. A heater & a kettle are normally less than 26A, but even if they were it wouldn't run for long.

has it achieved anything in practice?

NT

[Adam Funk]

If you shave the yak to reduce thermal insulation, is it allowed to carry more current?

[John Rumm]

Perhaps, but too much dried fruit, and it will probably crap on your floor!

[Stephen]

I hadn't thought of that, I will have a look.

[Stephen]

I like this idea. You could use the same MCB for the fire alarms. I suppose there is no right answer and there are arguments for and against all approaches, for example, you could argue if this MCB tripped you would lose all stair lights, not just one, so should each stair light be on a different floor's MCB? But how often do light circuits trip MCBs? I'm probably thinking too hard about this.

Thanks, Stephen.

[Stephen]

Can you push a JB into the ceiling void or does that fall foul of the accessible rule?

[Stephen]

I hadn't thought about that. That's a good idea.

Should I worry about trying to fill the odd gaps between the joist and insulation?

I am trying run a wire between the two bedrooms, so that I can remove the shared neutral from the stair light. I get halfway and then hit something. I did buy the inspection camera from aldi, not for this but because I thought it might be useful one day. I think the obstruction is too far away to see what it is and I find the camera a bit difficult to point in the right direction. I think I would be better with a 5m usb camera taped to the end of a rod.

Thanks, Stephen.

[Stephen]

I notice that this says that cables should be clipped every 250mm horizontally or 400mm vertically. How often is this done in reality?

I'm thinking that cables are often pushed along with rods and pulled through, and the only support is the cable resting on the plasterboard ceiling below.

When the cable goes down to a light switch or up to a socket, isn't the cable just handing in mini conduit, rather than clipped to the wall?

Thanks, Stephen.

[John Rumm]

I would not be too anal about it - its a belt and braces thing designed to buy a little extra time. So avoid big unfilled bits, but by the time you have tucked an appropriate width of glass fibre/rockwool in there it ought to be pretty full without much trying:

You can also get small torches designed to go on the end of cable rods, which can help:

(although I found that it had a different thread than my cheap rod set, so I had to make an adaptor for it:

Most of the long USB cameras you get from ebay etc also have light built into the end of them.

[John Rumm]

Frequently - when you can get to the cable and there is nothing else to support it.

If you read on to the "Under floors" bit shortly after it covers that. In a void between upstairs floor and downstairs ceiling, then its common to just rest on the ceiling - especially if its retrofitted. (if during first fix the cable was put in before the ceiling was plasterboarded then obviously it will need to be clipped to the joist or under capping).

Kind off, but its still supported to an extent by friction from the conduit or capping etc. What you want to avoid if possible is a great length of cable simply dangling from a single support point.

[John Rumm]

No, that's fine. Ideally it ought to be a type with cable restraints built in (e.g. like the wago boxes) since unlike the more conventional use of a JB you won't be able to clip the cables to something solid near entry to the JB.

[John Rumm]

Light circuits with mains halogen or in some cases even normal GLS tungsten lamps are quite prone to tripping a MCB when a bulb fails.

I fitted "non maintained"[1] emergency lights to the hall and landing lighting circuits. So when either circuit loses power for any reason the emergency lights come on.

[1] "Non maintained" means that they are only functional on loss of power. "Maintained" ones can also be manually switched on to be used as a normal light.

(I normally put a maintained emergency light near to the CU, so it comes on automatically of something trips, but you can also turn it on to read the meter or whatever).

[Stephen]

Thanks. It seems they have only filled the depths of the new joists and not the whole ceiling void, which may reduce fire resistance but does give me a gap to thread cable. The insulation only seems to be between the two iron girders, not the bit between the girder and the eaves, so I am not sure what is stopping the flames going up and around the loft conversion?

I was thinking I would use celotex or kingspan for any future insulating. Are these as fire retardant or must rock wool always be used for this?

I see you can get fire resistant plasterboard. Does it have to be used in a certain way to form a fire barrier, e.g. edges sealed with something intumescent?

I think my rods are made by draper but I think they came from TLC. I will have to email and ask them if it will fit. I did manage to get the wires through although I had to make a couple of holes to see where the cable was stuck.

I used to buy cable from tool station but paid a bit more and got the persimmon reels in boxes from Screwfix, hoping the cable would rotate in the box so the wire would come out with no twists. The twin brown worked as intended but the blue/brown just rolled out of the box! Perhaps because it was a bigger, heavier reel? I don't know if I would pay the extra for the boxed version again as they didn't seem to work for me.

Thanks, Stephen.

[Stephen]

Yes, I had forgotten that, I have tried to switch to CFL and now led.

That's a good idea but I don't think they will pass the aesthetic test of my other half!

[Andy Burns]

kingspan burns quite well ... I think you can buy a version sandwiched between non-flammable boards

[Tim Watts]

I tested some Ballytherm PIR and whilst it produced a nasty smoke, it did not support combustion by itself (extinguished as soon as the source was removed). I thought all the "celotex" products were like that?

[Andy Burns]

Actually I tested celotex, not kingspan, but I assume they're similar, my 2x2x2cm lump burnt pretty well, seemed to release a flammable gas or liquid onto its own surface that flared up and burnt for several seconds after removing from the cooker flame, a larger block might well char the surface and leave the core unburnt?