T+E totally enclosed in thermal insulation, Also downlights.

[tigerpaul]

Hello Folks,

Currently I am wiring a customers kitchen and diner.
We're using 1mm T+E for Lighting
6mm for cooker, 2.5 for everything else.
He is filling the ceilings with thermal/acoustic insulation after wiring and before the ceilings go up.
Now then, Table 4D5 states the following current carrying capacities for ref method 103
1mm = 8A
6mm = 23.5A
2.5mm = 13.5A

Surely I dont have to derate this by half because of the thermal insulation??

Also, customer want downlighters. Am I right in saying that the only downlighters he can have where the themal insulation is going to cover them are Aurora's SOLA range?

Cheers!

 

[Octopus]

Are you sure you're not using 1.5mm T&E?

"Surely I dont have to derate this by half because of the thermal insulation??"

When did you do your training?

Regarding insulation and downlighters you need to make sure that you install the lights to the manufacturers instructions and that you give a copy of the "air gap" information to the person installing the insulation.

 

[Darkwood]

When cables are subject to a current that approaches the rating of the cable it will create heat, under normal circumstances this heat can escape into the surrounding air and materials, this is taken into account when you work out your cable calcs, now when insulation is layed across your cables then the heat cant escape and if run close to their max design load then this heat will build up creating resistance which in turn creates more heat and so on until you have an overheating cable, then your in a possible fire hazard situation. Having your cable passing through insulation even if the majority of the run is free of it means the de-rating factors must be applied to the whole cable.

When applying and using regulation its always better to understand the reasons behind them, alot of electricians follow regulations blindly and when a odd situation comes up that hasnt been covered in their training then they cant make an educated decision and are prone to making poor judgements which can effect many things from safety to profits.

 

[MarkieSparkie]

Hello Folks,

Currently I am wiring a customers kitchen and diner.
We're using 1mm T+E for Lighting
6mm for cooker, 2.5 for everything else.
He is filling the ceilings with thermal/acoustic insulation after wiring and before the ceilings go up.
Now then, Table 4D5 states the following current carrying capacities for ref method 103
1mm = 8A
6mm = 23.5A
2.5mm = 13.5A

Surely I dont have to derate this by half because of the thermal insulation??

Also, customer want downlighters. Am I right in saying that the only downlighters he can have where the themal insulation is going to cover them are Aurora's SOLA range?

Cheers!

You most certainly do have to de-rate your cables if they are to be surrounded by thermal insulation ... 523.7 applies.
I would use fire rated downlights and as Murdoch says "provide the person fitting the insulation with any necessary air gap spacings", also don't forget the requirements of the Building Regulations, Part B, particularly compartmentation and fire-stopping.
How do you intend to inspect/certify the work? I personally would not be happy letting the client do the insulation work in this critical fire risk area unsupervised. At the very least I suggest you should insist the ceiling is not fitted until you have inspected and approved the insulation work.

 

[Richard Burns]

The values you have given (from table 4D5) are the derated values. Derating is from best case to existing case. So CCC for 1mm in free air is 16A. If in thermal insulation for more than 500mm and not touching a solid surface then half the CCC in free air, therefore 8A CCC. this is the value for method 103 as shown in 4D5.
However do try to see if there is any way of avoiding the cables being away from all surfaces.
Only really cause problems when doing standard RFC as you cannot use 32A breaker.

I am sure someone else did insulation coverable down lighters but sorry can't remember who.

 

[Jimmyb]

The values you have given (from table 4D5) are the derated values. Derating is from best case to existing case. So CCC for 1mm in free air is 16A. If in thermal insulation for more than 500mm and not touching a solid surface then half the CCC in free air, therefore 8A CCC. this is the value for method 103 as shown in 4D5.
However do try to see if there is any way of avoiding the cables being away from all surfaces.
Only really cause problems when doing standard RFC as you cannot use 32A breaker.

Re the ring final, if all cables all clipped to beams then it is ok to use 32a mcb.

 

[tigerpaul]

The customer is supplying everything, that is why he chose 1mm T+E as its cheaper.
When I got to the job the spec changed so the number of downlights went up. Then after I'd wired most of it did the customer tell me that he was putting insulation up and he wanted it to fill the gap between the joists. By then all the cables were in run through nice holes in the centre of the joists so they were going to be totally enclosed in the insulation.

This created a worry for me so I went back to the OSG which is what I had handy and found the table I referred to earlier.

Anyway, I've had to return to the job and I ripped out and rerun most of the circuits along one wall and told the customer to keep the insulation to one side of those. Thats leaving the lighting circuit which I've now split into 2 circuits thus reducing the design current.

I am aware that cables run in insulation for longer than 500mm are subject to a cable factor of 0.5 but I didnt know if the values given in Table 4D5 were already derated or not.

Regarding the downlights, Aurora SOLA range are designed for applications where the fitting itself is totally covered in insulation. All the others I have seen require an insulation free space to be created around and above the fitting, which is not what the customer wants in terms of acoustic insulation.

I wondered what others thought about this.

 

[Richard Burns]

Sounds like you have sorted the CCC issues (hopefully at customers expense)

Apparently after a search the ones I had thought of were the Aurora ones but they do seem to be OK to be covered with insulation.
I am not too sure on levels of acoustic insulation but I thought you could manage with fairly thin layers, depending on the noise you are trying to stop. Teenagers playing heavy rock at full volume might be a problem!
Just putting a rigid fire hood over the downlight may be enough, but it does not sound like it from your post.
You might be able to use SMD LED lamps that are cool running but this would not necessarily comply with the manufacturers instructions for the downlight.
Other than that either the customer has lower sound proofing (or puts down thick carpet/underlay) or you have the Sola lights.

Good luck

 

[JamesBrownLive]

Only really cause problems when doing standard RFC as you cannot use 32A breaker.

Is that because the CPD must not be more than 1.45X Iz ?

 

[Richard Burns]

The CPD being 1.45 xIz is accounted for by the characteristics of circuit breakers that means in reality so long as Iz in greater than In you have complied with the regs.

The CCC for 2.5mm totally enclosed in insulation is 13.5A when this is doubled for a ring as you have conductors in parallel you get 26A for total CCC therefore you cannot protect the cable with a 32A breaker.

 

[JamesBrownLive]

The CPD being 1.45 xIz is accounted for by the characteristics of circuit breakers that means in reality so long as Iz in greater than In you have complied with the regs.

The CCC for 2.5mm totally enclosed in insulation is 13.5A when this is doubled for a ring as you have conductors in parallel you get 26A for total CCC therefore you cannot protect the cable with a 32A breaker.

Yeah, just clicked. Must be having a blonde moment. Mental note to self... think more before asking dumb questions.

Cheers