17th edition and notifiable work.

[festive]

After hitting rock bottom on my extension budget im trying to get everything finished whilst attempting to 'stick to the book'. So whilst im paying for a qualified spark to replace the CU with a twin RCD unit as per 17th edition guidelines, im looking at doing the below myself, i consider myself competent, and tidy in my work, but no way near the level of a pro sparky. I have some questions, and really would appreciate some input:

1. We've had our Loft room rebuilt, and a ground floor extension added, in the process new floor joists were installed on first floor, so all current wiring that ran along the ceiling, is laying on top of the new floor joists. Ive done some reading up to see all cables if not SWA'd or similar should be at least 50mm below depth of joist, (as these are 170mm joists the center of the joist) Does each cable have to pass through it's own hole, as there must be a mixture of 20 or so 1.5/2.5mm t/e cables.

2. What if i use Celotex in the floor cavity, the cables have to pass above or below? OR do you cut slots in the celotex , the same for Rockwool, do you sandwich between rockwool?

3. I also have a large run of cables running down the side of the loft room walls (in the loft in the eaves area), previously all the cables were routed via a large U-section open conduit (now smashed up by the chippies!). Can i use this method again? I dont really want to tack each cable to the perlins? Or is that regs now? I did purchase some of those clips you can push into pre drilled holes which you can loop cables ties from.

4. The existing ring main for the loft room is in tact, as is the lighting spur. I've read

Replacement, repair and maintenance jobs are not notifiable, even if they are in a bathroom. (page 8 of part P approved doc, note b)

Is this still the case for 17th? Although all the cable is still the older spec 'white' twin/earth, whilst it seems in relatively good condition, i may wish to replace a few segments, what happens then?

TIA

 

[JohnD]

on item (2), the cable must not be buried in insulation. If it is lying on top of it, that is OK, since warm air can escape from it. You can actually put it under the insulation if you want, if heat can escape through the ceiling below, but this is not so good since the airspace will be warmer.

It is preferable not to bunch cables together as you are supposed to derate their current carrying capacity. It does not matter for domestic lighting cables fused at 6A (which is normal) since this is way under the cable capacity.

There is a way of laying cable on "cable trays" which is like a perforated metal channel you can run in roof spaces or similar, where you lay the cables on them and if you want retain with plastic ties to stop them flopping about. Since they are in free air you do not have to derate, and they are not likely to be trampled on or tripped over (this is a great risk if cables are on top of joists in a loft). you could so something similar but cheaper by nailing a plank to a convenient position and clipping your cables to it. You could use plastic trunking with the lid off, but the cables would tend to bunch together and get warm.

on item (4) you can replace odd bits of cable if they are damaged, and you can add extra lighting points or sockets without notifying, unless they are in a kitchen or bathroom. this will often involve extending or adding cable.

 

[festive]

Thanks for the reply, can anyone answer question 1? IE does each cable have to run through it's own hole a few diameters apart from the next, if this is the case im going to have a channel single cables spanning across a good metre or so through the joists!

 

[Chri5]

Cables grouped together require derating, in theory that applies to multiple cables run through a joist.

Holes in joists can be up to 0.25 joist depth, so with 170mm joists that amounts to 42 mm hole, Further holes can be added no less than 3 x the hole diameter (centre to centre) or on the above figure 3 x 42mm or 126 apart.

Could I suggest that in a loft perimeter cabling clipped direct to the eaves stud is the way forward. More so when 80% of sockets are likely to be positioned on the flat face wall of the eave.

 

[festive]

Could I suggest that in a loft perimeter cabling clipped direct to the eaves stud is the way forward.

So you're saying each cable needs to be clipped to the eaves studwork as opposed to all layed together in a Galvanised Cable Tray?

 

[ColJack]

you can notch joists for cables, but the notches ( IIRC ) have to be no more than a quarter of the way along the length of the joist..
and there's a maximum depth also, but I can't find my book right now to look..
you also need to provide some form of protection from nailing through the cables.. a 3mm steel plate or such would suffice..

is your loft room already floored out?

if not then you could put 2x1 or 2x2 timbers on top of the joists and leave gaps for the cables to pass through.. that way you don't weaken the joists, but you do lose an inch or two in the room height, and it messes the stair tread height up a bit...

 

[festive]

Ok i took a photo to illustrate what im talking about here, so i make a cutout along the top of the timber (horizontally) and cap with some metal plating Or can i? OF course it would save me alot of work disconnecting and rethreading all those cables! And if i can't can i cut a slot just above the old joists, or that's alot of timber to cut through.

Gonna be fun this, suppose i have to trace each cable back to CU and re thread.

 

[Taylortwocities]

Here's a decent guide to drilling & notching.
Dont exceed this or Building Control will be unhappy.

http://www.stevenage.gov.uk/stevena...tching-joists.pdf;internal&action=save.action

Dont do it like this!

View media item 5370

 

[festive]

Thanks TTC I popped out and bought the IEE 17th edition on-site guide. It mentions the notches but no actual criteria for it

This is much clearer thanks v much for your help. Doesn't seem to mention any sort of capping over the notches like steel plating? Something i think i shall add.

Ps your image seems v small like a thumbnail, would like to see a larger version of this!

 

[Taylortwocities]

Here you go. This should be better:
Shows how nice kind plumber has decided to "notch" out the joist over existing cable run.

Image courtesey of ebee I believe.

Untitled

• Taylortwocities
• 12 Oct 2008
• 10

Builidng regs dont mandate steel plates of nothed cable runs. They are a good idea but not a 'cure all'. Nail guns go right thru them.
see them here http://www.tlc-direct.co.uk/Main_In...Index/Necessities~Cable_Protection/index.html