Loft boarding in relation to wires and insulation.

[kevsterdiy]

Evening all.

About a year ago when I moved in to my house I noticed the lighting wires in the loft were 1.0mm T&E which was under the insulation, although not hugely thick, two thin layers totalling about 90-100mm. I rolled back the insulation to move the wires so they run over the top.

I have now started boarding some of the loft area, about a quarter, all I want to check is that to board over these wires that lay on top of the insulation is ok? (They are the small T&G, 18mm think chipboard)

None will trail over timer and be swashed of course.

Thanks,
Kev.

 

[notb665]

You are not supposed to trap the cables. Cut away some insulation so the cables rest on the ceiling or re-route the cables.

And aren't lighting circuits supposed to be 1.5mm2?

 

[kevsterdiy]

You are not supposed to trap the cables. Cut away some insulation so the cables rest on the ceiling or re-route the cables.

And aren't lighting circuits supposed to be 1.5mm2?

Not when my house was built (1976), 1.0 is minimum.

I was under the impression that 1.0 is ok over insulation, 1.5 is ok under. but wanted conformation of boarding over...

 

[JohnD]

Assuming it is on a 6A MCB or a 5A fuse, it will be OK. lighting circuits are very lightly loaded and even a 1mm cable is well inside its capacity even when derated for thermal insulation.

Immersion heater and electric shower cables, however, must be exposed to the air as they are loaded nearer to their capacity.

We can do the calcs if you like but it is rather tedious and the results will be as i have indicated.

 

[kevsterdiy]

Assuming it is on a 6A MCB or a 5A fuse, it will be OK. lighting circuits are very lightly loaded and even a 1mm cable is well inside its capacity even when derated for thermal insulation.

Immersion heater and electric shower cables, however, must be exposed to the air as they are loaded nearer to their capacity.

We can do the calcs if you like but it is rather tedious and the results will be as i have indicated.

Thank you - I can imagine there are many houses with both 1mm and 1.5 under board and over insulation. Evn more with 1mm under both.

Yes the circuit has a 6Amp MCB although both upper and downstairs circuits are together in one MCB. I can always get this split in to two separate MCBs is it is advisable?

The only other thing is a power shower with 1.5 cable that runs on .43 Amps - so well within.

I would assume with the age of house with the older style consumer unit that was removed when the new one was fitted that they were wired as one because there is spare space?

 

[JohnD]

it is preferable to have upstairs and downstairs lighting on different circuits, so that your house is not plunged into darkness when a bulb blows and trips the MCB.

You are not required to have separate circuits, though, and a single circuit is electrically safe and unlikely to be overloaded unless you have several large chandeliers or are obsessed with downlighters.

I expect you are moving over to CFLs (energy saving lamps) anyway so the total load will be very low, and trips will be very rare.

 

[kevsterdiy]

it is preferable to have upstairs and downstairs lighting on different circuits, so that your house is not plunged into darkness when a bulb blows and trips the MCB.

You are not required to have separate circuits, though, and a single circuit is electrically safe and unlikely to be overloaded unless you have several large chandeliers or are obsessed with downlighters.

I expect you are moving over to CFLs (energy saving lamps) anyway so the total load will be very low, and trips will be very rare.

Indeed. We will soon have to change over and the load will be far lees - very good point!

At least when they wired a cupboard light they did that on a different MCB so you can see the CU.