Insulation & Electrical Cable

[Waka]

Not sure if I dreamed this or it was on the forum, It relates to the compatibility of the slab type insulation like Extratherm and power cables.
I think someone said the power cable should not be run close to the insulation. Is this true and if so why?

 

[Alan Smith]

Yes I believe this is correct. Polystyrene in contact with cable breaks down the insulating sheath, presumably by outgassing of solvents from the polystyrene? Solution I was advised to use was urea formaldehyde insulating sheet rather than polystyrene (also better fire performance). I believe there is also a new form of cable insulation which is not susceptable. Not 100% sure about that though.

 

[StevieB]

If its for a workshop new build or rewire then an alternative would be to run your cable through 20mm conuit if the insulation is already in place, but it can be a pain to get cables doubled up through the 90 degree bends sometimes (DAMHIKT). If its for the house then that may be a non starter from a practical point of view.

Steve.

 

[StarGazer]

Polystyrene leeches out the plasticiser from the cable insulation so not advised to be in direct contact. Kingspan, Celotex, rockwool, fibreglass OK from this point of view.

Other aspect of this is that cables running in/under insulation may need to be derated. Running on top of insulation is OK.

 

[Waka]

Guys

Thanks for the info. It is actually going to be for the workshop extension, all I'll do now is have the wires running in conduit on the outside of the boarding that covers the insulation. That will actually match the rest of the workshop.

 

[brianhabby]

Guys

Thanks for the info. It is actually going to be for the workshop extension, all I'll do now is have the wires running in conduit on the outside of the boarding that covers the insulation. That will actually match the rest of the workshop.

It'll make it easier to modify the installation in the future too,

regards

Brian