Loft insulation and electrics

[whistler]

I know there are several other postings on this topic, but they always seem to refer to lighting cable which is not usually too much of a problem, or shower cables which must definitly be laid over loft insulation.

My query relates to the ring main. As i live i a bungalow, the ring main is routed through the loft and down the walls to the sockets. The cable is clipped to the joists in the loft and there is no slack to route it over the insulation.

So whats the answer? Will the contact with the joists allow enough heat dissipation, or do I still need to keep the insualtion away from the cables?

 

[GaryMo]

Method 100# - 2.5mm T&E clipped to wooden joist above a plasterboard ceiling with thermal insulation NOT exceeding 100mm in thickness - 21 AMPS

Method 101# - 2.5mm T&E clipped to wooden joist above a plasterboard ceiling with thermal insulation exceeding 100mm in thickness - 17 AMPS

The above assumes insulation has a minimum U value of 0.1 W/m2K

A ring final wired in T&E protected by a 30/32 protective device should have a current carrying capacity of not less than 20A for its particular installed conditions.
So, from the above, if you have more than 100mm of insulation it won't comply if wired in 2.5mm T&E.

 

[FingRinal]

And with a Government barely able to print, let alone write in joined-up writing, I wonder if their brilliant idea to insulate, insulate, insulate, will result in more house fires due to overheated cables which in turn they can use to justify more Draconian Part P-style red tape (i.e. tax and VAT)?

How many of the insulating companies will give a monkey's how their work affects Part P of the Building Regs and how many will issue a certificate that states their work complies with all relevant parts of the Building Regs?

It's going to make standard price (extent and lims) PIRs in domestic properties much harder. Does one tear up the insualtion to inspect the cables and thus impair the insulation, or does one just leave it, rely on insulation resistance testing and recommend all cable szies in the loft are upgraded before taking the easy way out and giving Unsatisfactory all the time.

 

[hairyben]

And with a Government barely able to print, let alone write in joined-up writing, I wonder if their brilliant idea to insulate, insulate, insulate, will result in more house fires due to overheated cables which in turn they can use to justify more Draconian Part P-style red tape (i.e. tax and VAT)?

How many of the insulating companies will give a monkey's how their work affects Part P of the Building Regs and how many will issue a certificate that states their work complies with all relevant parts of the Building Regs?

It's going to make standard price (extent and lims) PIRs in domestic properties much harder. Does one tear up the insualtion to inspect the cables and thus impair the insulation, or does one just leave it, rely on insulation resistance testing and recommend all cable szies in the loft are upgraded before taking the easy way out and giving Unsatisfactory all the time.

one of many examples of lack of working knowledge and failure to address real-life scenarios in the new regs.

Why can cables not be sleeved with a product that'd allow an acceptable air gap, say 2" slip on (side entry) flexiduct, before insulating?

 

[JohnD]

Why can cables not be sleeved with a product that'd allow an acceptable air gap, say 2" slip on (side entry) flexiduct, before insulating?

You are talking about cables in a conduit, where the conduit is buried in insulation?

tell me where you think the heat will go.

then look up the rating factor and tell me what it is.

 

[hairyben]

Why can cables not be sleeved with a product that'd allow an acceptable air gap, say 2" slip on (side entry) flexiduct, before insulating?

You are talking about cables in a conduit, where the conduit is buried in insulation?

tell me where you think the heat will go.

then look up the rating factor and tell me what it is.

heat loss is relative- I say 2" because thats several times the area of what we call conduit, there is a point at which a sleeve should be large enough to consider a cable to be in free-air like conditions.

 

[whistler]

If for example I installed a thin piece of wood vertically approx one inch from the joist thus holding back the insulation and leaving an air gap above the cable. Would this be satisfactory?