Cable routing in the loft / attic

[sheep65]

I need to replace the lighting circuits (no earth) and I have been trying to find out what the regulations are re installing the cable in the loft.

The loft is normally boarded out (storage) and so I assume it would not be good practice to route the cables under the boards because of the insulation and the lack of accessibility. I am wondering whether I can route the cables via the rafters rather than installing them on top of the boards.

Could someone please advise what I can / can't do.

 

[oharaf]

I would suggest you lift the floor, remove any insulation in the areas you wish to run the cables.

They could be laid under or on top of the insualtion but you would need to carryout some calculations regarding voltagedrop etc.

You will also need to replace the switch drops.

You will also need to ensure that the circuit has RCD protection and if you are installing in the bathroom, then this then becomes notafiable works.

You will also need to inspect, test and certify the works.

As you will be re-boarding the loft then junction boxes become a no no pretty much, so you will need to know how to 'loop in loop out' at the ceiling rose.

I am assuming the upstairs lighting is seperate from the downstairs lighting circuit? If not then you are into a different ball game

 

[ColJack]

voltage drop has nothing to do with the amount of insulation it's under..

even when under more than 100mm of insulation a 1.5mm² cable is rated to 13A. more than adequate for a 6A lighting circuit..

boarding out the loft however then causes the installation method to change..

if it's clipped to a joist and touching the ceiling or the underside of the loft boards then it's 16A, if it's not touching the ceiling or loft boards ( ie clipped center of joist as they tell you to install it ) then it's 10A, which is still enough for a 6A lighting circuit..

 

[sheep65]

It's currently 1 lighting circuit (upstairs and down) but I am now putting separate circuits in. I'm familiar with the loop-in system and was planning to use that upstairs anyway.

Downstairs I was going to use a jb box system (2-way switching per room & multiple lights per switch) and site the jb behind the 1st light of each set; is this acceptable ?

I know about the bathroom / kitchen, so will be leaving those connections to the electrician, however, there is nothing to stop me routing the cables to the connection points is there ?

The idea was that the electrician would do the kitchen / bathroom installs & test the remainder of the house when he puts in the new cu.

 

[Chri5]

Downstairs I was going to use a jb box system (2-way switching per room & multiple lights per switch) and site the jb behind the 1st light of each set; is this acceptable ?

make sure the termination is accessable when the light fitting is removed. See wiki for lighting diagrams with block connections.

I know about the bathroom / kitchen, so will be leaving those connections to the electrician, however, there is nothing to stop me routing the cables to the connection points is there ?

Since you could deem the work to be mtce, run them and connect, but do get the electrician to test them when he replaces your CU.

The idea was that the electrician would do the kitchen / bathroom installs & test the remainder of the house when he puts in the new cu.

Some might get funny about testing off other peoples work (since he can't be expected to know the cable routes). Best way forward would be a PIR full test pre start. That will tell him the condition of all the cabling at the property and will allow you and him to quote fixed price for the CU and any remedials that might turn up due to the PIR testing.

 

[rebuke]

I know about the bathroom / kitchen, so will be leaving those connections to the electrician, however, there is nothing to stop me routing the cables to the connection points is there ?

If you're going to be burying cables in the wall, then check with your electrician first, as if he is signing off on the work in the bathroom/kitchen then he must be satisified that they are installed correctly (i.e. in safe zones etc) - if he turns up to wires poking out re-tiled walls etc, he may just refuse to sign off on them...

 

[Chri5]

Single way lighting via block connections

Two way via block connections

You must not have j/bs that are inaccessable (hidden, under floors, in ceiling voids- that can't be got at).

A j/b is service required item and as such MUST be accessable.