Loft wiring

[frank999]

Hello, hope someone can help.
I am about to start wiring a loft extension, hopefully I will find an electrician that is happy for me to lay the wires, with him making the final test and connection.

In the loft I have a bathroom and living area, can 1 RCD cover both these areas, or do I need 2 circuits for each, each with 30mA protection ?

As the new circuit/s are RCD protected, a 12v bathroom extractor fan in Zone 1 is acceptable?

I am going to install 2.5 T&E for the lighting circuits - in case it runs through any insulation, is that a correct method where the cabling encounters insulation (100mm PIR)

I will also run cable to these along the 150mm safe zone (NICEIC safe zone diagram) at the top of the wall behind battened 12.5mm plasterboard, as all new wiring is RCD protected, I assume that will be OK?

Thanks

 

[ricicle]

You need the electrician on board before you do anything. It is not necessary to derate lighting cables in insulation.

 

[stillp]

It is not necessary to derate lighting cables in insulation.

Yes it is, but the derating usually has no practical effect.

Pedantic? Moi?

 

[Taylortwocities]

I am going to install 2.5 T&E for the lighting circuits -

From a purely practical viewpoint, you'll not get 2.5mm² conductors into many light fittings. And Light switch boxes are usually too cramped to allow fat bits of copper in there.

 

[sparkwright]

As said, do not use 2.5 mm2 for the lighting.

Use 1.5 mm2 if you must, but usually 1.0 mm is fine anyway.

 

[frank999]

1.5mm it is then, thanks.

Yes I will get one on board ASAP

Is it acceptable for just 1x 30mA RCD to cover both the bathroom and living area, or do I need 2x RCD's (ie one for each living area)?

 

[riveralt]

1.5mm it is then, thanks.

Why? What is the matter with 1mm² T&E? Its cheaper and easier to work with. What on earth do you intend to have on this lighting circuit?

Yes I will get one on board ASAP

One assumes you are talking about an electrician. If so, s(he) can design the circuit for you then and that will include the size of the cable and the answer to the next question.

Is it acceptable for just 1x 30mA RCD to cover both the bathroom and living area, or do I need 2x RCD's (ie one for each living area)?

 

[flyingsparks]

I hardly ever use 1.5mm on lighting circuits in a domestic situation. I hate the stuff! Makes life so much harder to terminate everything!

 

[securespark]

I've always tended to use 1 milli, but admit down the years to having been tempted by the 1.5 milli argument. Not any more.

1.5 seems to have been a fashion: at one point it was "in", now it is out.

Oddly, it seems in the past to have been used as a measure of "manliness" when comparing notes while waiting at the counter: hey, I'm one of the boys, I use 1.5 for my lighting circuits. Don't bother with him, he's a wimp, he only uses 1 milli. Cue lots of cruel laughing....