Loft insulation and ratings

[adsmith]

Hi guys

New build small 2 bed bungalow to have 300mm of insulation in loft space. Obviously all circuits to be ran in loft and dropped. Circuits to be used are alarm circuit 6amp, lighting 25x 4w downlights 6amp, 2 x 32amp ring mains, 16amp boiler radial, 32 amp hob/oven circuit (undecided if gas or elec hob)
What would your preferred method of running the cables in the loft space due to large amounts of insulation. Is it safe to have for instance the hob/oven circuit cable clipped to the ceiling joist under 300mm of insulation.

 

[BruvDunk]

Table 4A2 - Installation methods of cables may be a good place to start

 

[Pete999]

Table 4A2 - Installation methods of cables may be a good place to start

What BruvDunk said above.

 

[adsmith]

I see the installation method 101 (in contact with joist covered in excess of 100mm insulation) this is the most likely method I will have to go with however I have a question. Using this installation method it states the cable rating for 2.5mm cable is 17amp. (I presume that's for a radial circuit?) Is it still safe to run a ring main using this installation method in 2.5mm cable protected with a 32amp breaker because 17amp + 17amp = 34amp which is above my circuit breaker rating
Thanks

 

[Andy78]

I see the installation method 101 (in contact with joist covered in excess of 100mm insulation) this is the most likely method I will have to go with however I have a question. Using this installation method it states the cable rating for 2.5mm cable is 17amp. (I presume that's for a radial circuit?) Is it still safe to run a ring main using this installation method in 2.5mm cable protected with a 32amp breaker because 17amp + 17amp = 34amp which is above my circuit breaker rating
Thanks

See 433.1.204 for clarification on minimum ratings for ring final circuits.

 

[davesparks]

I see the installation method 101 (in contact with joist covered in excess of 100mm insulation) this is the most likely method I will have to go with however I have a question. Using this installation method it states the cable rating for 2.5mm cable is 17amp. (I presume that's for a radial circuit?) Is it still safe to run a ring main using this installation method in 2.5mm cable protected with a 32amp breaker because 17amp + 17amp = 34amp which is above my circuit breaker rating
Thanks

The rating is for any type of circuit, ring or radial.
2.5mm is not suitable for a ring final circuit with that rating, you would have to increase the cable size if you are sticking with this installation method.

Personally I wouldn't be happy installing cables under that much insulation.

 

[adsmith]

See 433.1.204 for clarification on minimum ratings for ring final circuits.

So 4mm is the minimum I can go for on a ring main for installation method 101? That's a pain. If I was to try change the installation method. For Instance fix a piece of wood across the rafters above the thermal insulation level and clip the cable direct to that then drop down through the insulation where the sockets are located would that be adequate as there would only be a small portion of the cable going through the insulation therefore I could use 2.5mm? Thanks for the reply.

 

[adsmith]

Or do you guys have any ideas or methods of installing cables in a new build bungalow that will have 300mm of loft insulation

 

[Andy78]

So 4mm is the minimum I can go for on a ring main for installation method 101? That's a pain. If I was to try change the installation method. For Instance fix a piece of wood across the rafters above the thermal insulation level and clip the cable direct to that then drop down through the insulation where the sockets are located would that be adequate as there would only be a small portion of the cable going through the insulation therefore I could use 2.5mm? Thanks for the reply.

It is always best to avoid contact with any forms of insulation with any cable type if at all possible.

 

[westward10]

Thread closed. Follow link to similar thread.

Loft installation methods

So new build bungalow is to have 300mm loft insulation as told by building control. This means installation method 101 comes into place however as it's a bungalow all circuits including cooker ring mains etc will be installed this way as they come from the loft space down. This installation...

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