Shower Cable and insulation

simon bartlett · Jun 24, 2023

Hey all,
Ive been in and out of a huge house rewiring as the renovate it for a year of so. Every is thing done and dusted except the downstairs shower. I ran a 10mm from the CU to a stud partition where the Isolator sits and then onto the shower. About 15-20m in total.
Ive gone back today and seen that the shower the plumber installed is a 9.8kw so ill change the RCBO from a 40 to a 45A which is no problem however.... it appears they have used 60mm or 100m mineral wool insulation in the stud which I didnt consider. ( I know I should have)
I have no idea how they have insulated the cable for this 2m run ie 102 or 103 as i wasnt there when they insulated and boarded but according to the regs book it is now either rated to 47A or 32A depending on wether they sandwiched the cable or just pushed it back against the plaster board.
Asking the homeowner to change the shower is very unappealing as he would be limited to 7kw and its already plumbed in.
Clearly I cant derate the RCBO to 32A etc and I cant change the cable either.

How would you guys proceed regarding the insulation ? Would you even change the RCBO over ? I cant imagine its likely to trip drawing 42.6A on a 40A RCBO
I really appreciate the guidance of you guys in here on this.

loz2754 · Jun 24, 2023

If the isolator is on the wall, take out the back box and have a look inside the wall.

Risteard · Jun 24, 2023

simon bartlett said:
Hey all,
Ive been in and out of a huge house rewiring as the renovate it for a year of so. Every is thing done and dusted except the downstairs shower. I ran a 10mm from the CU to a stud partition where the Isolator sits and then onto the shower. About 15-20m in total.
Ive gone back today and seen that the shower the plumber installed is a 9.8kw so ill change the RCBO from a 40 to a 45A which is no problem however.... it appears they have used 60mm or 100m mineral wool insulation in the stud which I didnt consider. ( I know I should have)
I have no idea how they have insulated the cable for this 2m run ie 102 or 103 as i wasnt there when they insulated and boarded but according to the regs book it is now either rated to 47A or 32A depending on wether they sandwiched the cable or just pushed it back against the plaster board.
Asking the homeowner to change the shower is very unappealing as he would be limited to 7kw and its already plumbed in.
Clearly I cant derate the RCBO to 32A etc and I cant change the cable either.

How would you guys proceed regarding the insulation ? Would you even change the RCBO over ? I cant imagine its likely to trip drawing 42.6A on a 40A RCBO
I really appreciate the guidance of you guys in here on this.

It won't cause it to trip, but it still means that it's operating above the load it's designed to sustain and therefore also running hotter than intended. It isn't a compliant design.