Reference method 102

[jlh54]

Hi all,
First post on this great forum. Am just embarking on installing a ring circuit in my painfully slow and shoestring house renovation. Building control are notified etc and an inspection/testing scheme is in place so that side of things is sorted.
What's puzzling me is how to satisfy 102 in practice where I have to run through stud walls. 3x2 studs, with either 25 or 50mm acoustic insulation as required/deemed wise. So there's an air gap but I assume 102 still applies? Due to practicalities I've already installed boards on one side of a wall, sockets to be added opposite (currently open) side. I could notch noggins but how do I ensure cable is actually touching subsequently installed plasterboard without having enough insulation to force cable up against it? Do I need to run in conduit (2 cables at 2.5mm still ok as per 4d1a? Do I loop through the return cable)? I really don't want to have to use 4mm cable especially as due to the partial insulation depth there will be no genuine problems with heat dissipation
A related query is what method if any one needs to use to support the cable on vertical drops in a stud wall?
Many thanks for any constructive insights!

 

[PrenticeBoyofDerry]

Can you not clip the cable to timbers, keeping cable in safe zones or clip/fix directly to PBs

 

[jlh54]

Clipping to timbers is ok for ceilings but my copy of regs for 102 shows the t&e flat against the plasterboard, clipped to timbers in a wall seems to make it 103 no? I don't know what to use to clip/fix against the plasterboard.

 

[PrenticeBoyofDerry]

Are you looking at table 4A2 then 4D5, that shows/explains how to comply to this regulation. If you cannot comply to this with regards to current carrying capacity. Then you need to start thinking of an alternative, such as increasing cable size and changing the ref method.
You can still clip to timbers, providing cable is touching PBs and still remains in safe zones.

 

[EFLImpudence]

The illustrations for the different methods all show the voids packed with insulation thus forcing the cable into contact with the plasterboard.
As you have a 75mm. void with only 25 0r 50mm. insulation I am not sure if 102 really would apply.

 

[jlh54]

Right. So that's what I'm not sure about, if it doesn't apply then presumably I can clip to studs. But, apologies if I'm being stupid PrenticeBoy, if it does apply then I don't know of a clip that will force the cable to contact the PB - the ones I have would stand it off by a few mm, the thickness of the clip plastic itself. I only have the onsite guide with me, will have to check the big book later for 4a2

 

[jlh54]

Right. So, if 102 doesn't apply then what does? And if it does, what clips on the market allow you to give contact to subsequently overlaid plasterboard? This is vexing me somewhat as the rest is straightforward and I want to crack on...

 

[John D v2.0]

Even if a method says it should be in contact, that just means close enough to lose heat into the surface, so within 1/3 the diameter of the cable. It's not really an exact science, you just have to classify as best you can and hope anyone who checks it agrees with your decision.

 

[EFLImpudence]

I would say if it is actually in an air gap (touching at some places), this would be no worse than method B (in conduit) giving you 23A.

 

[JohnW2]

I would say if it is actually in an air gap (touching at some places), this would be no worse than method B (in conduit) giving you 23A.

Would it not be more like 'in conduit in a thermally insulated wall' - which, even if the conduit were (per diagram in regs) touching the inner skin of the wall, would be Method A (18.5A)?

Kind Regards, John

 

[EFLImpudence]

Would it not be more like 'in conduit in a thermally insulated wall' - which, even if the conduit were (per diagram in regs) touching the inner skin of the wall, would be Method A (18.5A)?

I don't see why. If it is in an air gap several times bigger than the conduit the, surely, that must be less onerous than in the conduit itself.

Plus, of course, is the conduit in an insulated wall if the void is only half-filled? Half insulated wall?
What if the wall had only an inch space with no insulation?
I refer you to the illustrations where the actual situation is not covered.

What about an insulated ceiling void where the cable is on top of the insulation? Method B?
What about an insulated loft where the cable is on top of the insulation? Method C?

 

[JohnW2]

I don't see why. If it is in an air gap several times bigger than the conduit the, surely, that must be less onerous than in the conduit itself.

I'm not sure that, in the case we are consdiering, it would necessarily be "several times" - but, no matter how big/small the air gap, "in conduit within an air gap at least partially surrounded by insulation" is presumably 'more onerous' than "in conduit in the absence of any insulation"?

Having said that, I agree that the situation in question is not exactly covered by the regs and that, in practice (and particularly given what we know about 'safety margins'), I would be happy to adopt your view and consider it as Method B.

Kind Regards, John

 

[EFLImpudence]

I would just say that it is not 'partially surrounded' by insulation.

That's what all the illustrations show.

 

[JohnW2]

I would just say that it is not 'partially surrounded' by insulation.

Well, it is - unless you're going to quibble about the fact that 'surrounding cannot be partial However, we are agreed that the regs are silent about this particular arrangement, and that it is reasonable to consider it as Method B.

Kind Regards, John

 

[EFLImpudence]

Well, it is - unless you're going to quibble about the fact that 'surrounding cannot be partial

No, I wasn't quibbly about that but -

When driving on the motorway, are you partially surrounded by the central reservation?