Installing sockets in loft, wiring query

[Octopus]

if an attic is insulated properly, i.e. between the roof rafters instead of on the floor, then the heat in summer is vastly reduced, and it doesn't freeze in winter. double bonus.

I'm a bit dubious about this new fangled insulation between the rafters .... just think about all the cold air venting the roof space..

Our extension was insulated between the rafters... and open to the existing lost which has the old itchy stuff ..... so I added the itchy stuff in the extension...... and I know the new part does get blxxdy hot in the summer too!

 

[hightower]

It's not scaremongering at all, fact seen it happen. Please don't insult me by trotting out the MCB will stop that happening, that's a crock.
When the op's 6a ? MCB has cleared an overload on multiple occasions then welded it's contacts together, ergo can't clear an overload. What happens then ?.

Anyway as far as I'm concerned, conversation over & done with.

What happens if the MCB fails on a circuit that can easily be overloaded by design, such as a socket circuit? So do we need to start lashing in 16mm twin and earth just in case?

 

[Pete999]

What happens if the MCB fails on a circuit that can easily be overloaded by design, such as a socket circuit? So do we need to start lashing in 16mm twin and earth just in case?

Have some trouble getting 2 16mm2 in a socket HT (JOKE)

 

[Midwest]

One might have to consider installing cables with a higher ccc, such as the picture the OP first posted, reg 523.9.

Appendix 15 gives informative guidance on cable size selection for ring final & radial circuits.

Reg 433.1.204 states 'accessories to BS 1363 may be supplied through a ring circuit......The circuit should be wired .........with a minimum csa of 2.5mm (except MI)'. Can't find a similar reg for radials, but guess there must be.

Seen cheeky single sockets, blagged of the first floor lighting, to power the aerial booster, but somebody could plug in a 3kw, for their 'hydroponics'

So when would that 6a mcb trip, and what current would flow through the de-rated cable?

 

[hightower]

An overload is an overload, doesn't matter if it's because too many lights on the circuit, or because a 13A socket outlet is installed off it. If a 1.5mm cable feeding a light can deal with an overload while the 6A breaker begins to work, why wouldn't a 1.5mm cable feeding a socket outlet work the same way? I'm struggling to get my head around people's arguments on here.

 

[davesparks]

Please show me where I've said such things? My post was merely in disagreement with what you said the outcome would be. A properly designed lighting circuit isn't going to burst in to flames - that's literally the first thing you learn at college. However, I agree with what everyone else has said about a dedicated circuit (or jumping off a more suitable circuit), I just disagree that (untrue) scare-mongering is the way to advise the OP to get a professional in.

But this circuit will not be a properly designed circuit once a DIYer has added sockets too it. And there's a pretty high chance that once they've tripped the mcb a couple of times they will solve the problem with a higher rated mcb.

 

[davesparks]

An overload is an overload, doesn't matter if it's because too many lights on the circuit, or because a 13A socket outlet is installed off it. If a 1.5mm cable feeding a light can deal with an overload while the 6A breaker begins to work, why wouldn't a 1.5mm cable feeding a socket outlet work the same way? I'm struggling to get my head around people's arguments on here.

Yes the 6A mcb will operate the same regardless of what caused the overload.

But the common way a DIYer solves the problem of an mcb tripping through overload is to replace it with a higher rated one.

You also need to think about the size of the overload, the regulations require that we avoid the possibility of long duration small overloads as mcbs can't detect small overloads.
If the result of this additional socket is a load of 7A then it will take a long time to trip, but in all that time the thermal element in the mcb will be sitting there slowly cooking itself.

I think, and experience suggests, that small overloads damage mcbs more often than cables. Normally this results in an over-sensitive mcb but every once in a while it results in an mcb failing closed.

 

[Midwest]

An overload is an overload, doesn't matter if it's because too many lights on the circuit, or because a 13A socket outlet is installed off it. If a 1.5mm cable feeding a light can deal with an overload while the 6A breaker begins to work, why wouldn't a 1.5mm cable feeding a socket outlet work the same way? I'm struggling to get my head around people's arguments on here.

Of course, I haven't got a outdoor socket for my deck lights, switched from inside on my downstairs lighting circuit

 

[Midwest]

559 Luminaires & Lighting Installations. Reg 559.5.1 connection to the fixed wiring. At each fixed lighting point one of the following shall be used for the termination of the wiring system;
(i) A ceiling rose to BS 67 etc, etc, etc
(v) A suitable socket outlet to BS1363-2
(vii) A connection unit to BS 1363-4

 

[hightower]

I think, and experience suggests, that small overloads damage mcbs more often than cables. Normally this results in an over-sensitive mcb but every once in a while it results in an mcb failing closed.

Well experience is something I can't argue against at this early stage in my career. And thanks for taking the time to explain it like that.

 

[Midwest]

Arrgh, I do like a happy ending

 

[hightower]

Arrgh, I do like a happy ending

You do end up paying more for them though. What? What?

 

[Santa]

A perfectly legal alternative would be to buy an extension lead with six sockets on the end and run the cable through the ceiling to a 13 amp socket. My computer, printer and a couple of chargers are plugged into an extension simply because I don't have enough sockets for them all.

Having an electrician wire up a spur would obviously be better but it's not essential.

 

[Midwest]

You do end up paying more for them though. What? What?

Words are free, its how you use them that might cost you (RJM)