Installation Methods

[Bucks01]

Can anyone help with defining the Installation Method example as attached below. Its for a new build bungalow that has PIR insulation in the floor (Underfloor heated), on the inside of all external walls and in the vaulted ceilings. So looking at the drawing attached as an option for an Installation Method, what Reference would best describe this? I'm trying to think of ways that would not compromise the integrity of the PIR yet allow the cable CCA to be kept to a minimum.

Regards
Michael

 

[Murdochcat]

What do you think ?

 

[Bucks01]

I dont know, thats why I'm asking. What do you think?

 

[Murdochcat]

Are you a spark

 

[Bucks01]

Are you?

 

[Murdochcat]

Retired spark

 

[Bucks01]

Time served since 1992, so whats your thoughts on my original qustion now we've established our previous career paths?

 

[ericmark]

I would say 102 Installation method for flat twin and earth cable in a stud wall with thermal insulation with a minimum U value of 0.1 W/m2K and with the cable touching the inner wall surface. If touching the brick wall, but 103 Installation method for flat twin and earth cable in a stud wall with thermal insulation with a minimum U value of 0.1 W/m2K and with the cable not touching the inner wall surface. If not touching it, is seems clear enough to me, so why do you ask?

 

[Bucks01]

Thanks Eric, the reason Im asking is no1- its not a stud wall and no2- its not in contact with any insulation. There is probably an air gap of 25mm to the insulation board and the cable is clipped direct to the brickwork. 102 does stand out, however PIR is closer to 0.022 W/m2k and the cable is not clipped to the outer wall surface (plaster board) its clipped to a cold surface (masonry) inside the wall. I'm not sure i can find a definitive method in BS7671. Its pretty critical as im struggling with the cable calcs.
Regards
Mick

 

[ericmark]

It is not an exact science, as we really don't know how much heat the brick will absorb. But I would think 102 is close enough. Installation method 100 and 102 would allow use of 2.5 mm² for a ring final, method 101 needs 4 mm² and 103 needs 6 mm² to be rated over 20 amp. It does mean less volt drop, 4 mm² good for 175 meters instead of 106 meters, and 6 mm² good for 270 meters.

However the problem is getting the cable into the sockets.

 

[JohnW2]

I'm not sure i can find a definitive method in BS7671. Its pretty critical as im struggling with the cable calcs.

Interesting. I think its one of those (a good few!) situations that has not been considered by BS7671, but it may well become a more common situation since a lot of people seem to be putting insulation over masonry walls (inside or outside) 'to satisfy EPC requirements'

In terms of intuition, common sense and looking at what BS7671 does say about various installation methods, I would personally doubt that it is any 'worse' than Method B (which isn't too demanding), would you?

What sort of CCC are you looking for? If there are remaining doubts/uncertainties, would it be too problematical to size the cable for the 'worst'(credible') scenario?

Kind Regards, John

 

[securespark]

In cases where I need clarification, I ring the IET helpline. Dunno if that is still a thing.

But you could use the WCS.

Worst Case Scenario.

Edit.
Sorry.......failed to read the full thread again.....

 

[EFLImpudence]

If the wall chase were filled before the insulation was applied, would it not be method C?

 

[Murdochcat]

What does your CPS technical support say?

 

[JohnW2]

In cases where I need clarification, I ring the IET helpline. Dunno if that is still a thing.

The trouble there is presumably that all one could get would be an individual's opinion, given that it is a scenario which BS7671 itself does not explicitly consdier.

But you could use the WCS. ... Worst Case Scenario.

Yes, as you have presumably now seen, I had already suggested that an an option.