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Insulation and thermal bridging and an EV charger

JohnE

The situation is a garage being converted into a TV room

External wall with batten attached which is to be insulated with 75mm PIR insulation and plaster boarded
Stud is only 70mm!!

Picture attached...

The house CU is high up on the wall. the tails ran down the internal garage wall to the outside meter box
A second CU was mid way down the wall feeding  an external EV charger, the tails of which also went to the external meter box

The tails were in plastic conduit surface mounded.

Since the tails (no RCD protection)to both boards are to be hidden by the plasterboard, I though best to put in two lengths of earthed metal conduit (50x50)
The 10mm feed to the 7kW charger is clipped to the batten.

The owner is doing the batten and insulation.
I am concerned about insulation being near my cables and trunking


I presume the trunking it self will be a break in the insulation so could be a thermal bridge?

Could you run the insulation up to the trunking or should they be a gap.

cables clipped along the batten how far should they be from the insulation,
I would like to leave about a 50mm gap? but this will cause this thermal bridge issue I believe?

Also say if  a 2.5mm  socket radial (fused to 16A) was ran through the batten and against the concrete block 
with insulation over it. What installation method would you consider that. I presume these soft concrete blocks have some insulation factor.
Will they be much of a heat sink?

I am concerned about the EV cable really as a continuous load in this stud work. Its has a bit of extra capacity as 10mm2 for a 7kW charger.

How can the wall be adequately insulated, without bridging and the cables be safe?

Thanks

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  • 0

    Sorry I won't keep on, one last thought on this.
    In the stud bay with the meter tails
    On the block wall install 20mm layer of  PIR type insulation
    Mount the metal trunking onto this or a thin ply layer if better
    Then plaster board over
    Ca ble not in insulation
    Good free air coverage
    plasterboard will enable heat dissipation
    thermal bridge reduced

    ?

  • 0 in reply to JohnE

    Table 4A2 should help, but for me, it seldom shows exactly what I want.

    The difference between numbers 2 and 60 seems to be largely the degree of insulation around the conduit. I find it difficult to believe that there would be any significant difference between round conduit and rectangular (or square) ducting.

    No. 2 has the conduit touching the inner skin, but yours touches the outer skin, which will be cooler.

    Page 431, RM A: "Heat from the cables is assumed to escape through the inner skin only."

    RM B: "Were the conduit is fixed to a masonry wall the current-carrying capacity of the ... cable may be higher."

    Your ducting is attached to the cool outer surface of the void.

    What is the probability of the main tails carrying 80+ A for an extended period?

    You have to choose between RM A and RM B. I think that if the bay between the studs is filled with Rockwool (or similar), you will not go far wrong.

  • 0 in reply to Chris Pearson

    Thank you Chris.
    Just to clarify a few thing I may be misunderstanding
    Is this with your earlier comment on the installation method that would require the service fuse to be  derated to 80A ( if its actually s  a 100A fuse) for this solution

    Chris Pearson said:
    Agreed, so now the DNO's fuse needs to be downgraded to suit.

    Chris Pearson said:
    I think that if the bay between the studs is filled with Rockwool (or similar), you will not go far wrong.

    Do you mean put rock wool in the bays either side of the section with the tails in,
    or put rock wool in the bay with the tails in (to limit thermal bridge issues)

    Many

  • 0 in reply to JohnE
    JohnE said:
    Is this with your earlier comment on the installation method that would require the service fuse to be  derated to 80A ( if its actually s  a 100A fuse) for this solution

    Yes, if you choose RM A.

    JohnE said:
    put rock wool in the bay with the tails in (to limit thermal bridge issues)

    Yes.

    JohnE said:
    you will not go far wrong

    Sorry, I should have added, "with RM B".

    Please note that I am no expert at all on insulation and where you put you permeable and impermeable barriers, etc.

    Sometimes, if you go by the letter of all of the building regulations, etc., the customer just cannot have what he (or she) wants. So, compromises are necessary and you do the best that you can.

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  • 0 in reply to JohnE
    JohnE said:
    Is this with your earlier comment on the installation method that would require the service fuse to be  derated to 80A ( if its actually s  a 100A fuse) for this solution

    Yes, if you choose RM A.

    JohnE said:
    put rock wool in the bay with the tails in (to limit thermal bridge issues)

    Yes.

    JohnE said:
    you will not go far wrong

    Sorry, I should have added, "with RM B".

    Please note that I am no expert at all on insulation and where you put you permeable and impermeable barriers, etc.

    Sometimes, if you go by the letter of all of the building regulations, etc., the customer just cannot have what he (or she) wants. So, compromises are necessary and you do the best that you can.

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