Insulation and thermal bridging and an EV charger

In the original drawing in the first post there are 2 cross sections, one with the insulation between the battens and one with it on the surface of the battens. If the owner does the second, a lot of the problems disappear.

Couple of things spring to mind, if the tv is wall mounted there might need to be studs inset into the insulation for support. And if the CUs are metal, and presumably not brought forward to the new surface, they could suffer from increased condensation as they will be colder than the air in the new room

Thank you.

Can quite visualise you plan Andy

AJJewsbury said:

I'd probably run the tails on the surface in PVC trunking inside then dive through the insulated wall for the shortest distance to the meter box.

On the surface of what ? please

The owner is thinking of not insulating the section with the tails, but that could be an issue?

Ive attached another pic.

The tails and main board do not line up
The main boards tails are outside of any zones.

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

?

On the surface of what ? please

Interior surface - i.e. on top of the plasterboard. That way they're not concealed so all the issues zones or concentric earth protection, not to mention being embedded in thermal insulation all go away (apart for the short distance through the wall to the meter box). If the customer is happy with two CUs surface mounted on that wall, a bit of extra trunking shouldn't be too hard a sell.

The owner is thinking of not insulating the section with the tails, but that could be an issue?

It's pretty rubbish from a thermal point of view - with risks of condensation both on the plasterboard surface and against the original wall (risking rot of the studs - the pictures seem to suggest untreated timer is being used too )

   - Andy.

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.

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

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.

and, if it is more than 50mm below the celotex, cable is out of zones anyway. 

It would be better in terms of cable rating if the tails could use the blockwork as heatsinking. It is probably not so good from a room thermal and condensation damage perspective.

Mike. 

I presume these soft concrete blocks have some insulation factor.
Will they be much of a heat sink?

Presuming we're talking aerated concrete blocks here (e.g. thermalite or celcon) - the ones that usually have squiggles on their surfaces and look like an aero bar when broken - then yes they have a bit of insulating property - although not a huge amount.  Lambda values (W/mK) are around 0.15 - which compares with timber, conventional concrete blocks are closer to 1.1 (so about 7x as thermally conductive) whereas "proper" thermal insulation is more like 0.033 (wooly stuff) or 0.022 (PIR/PUR board - kiindspan or celotex) (so about 1/7th as thermally conductive as aerated blocks).

  - Andy.

Would it not have been simpler to have lowered DB2 to the same height as the meter box as all the cables from it appear to go down anyway. Just put it behind some furniture flushed in.

Gary