RCBO query

[diy_fun_uk]

Existing installation.

9.5kW shower
6mm cable
40A RCBO

Has worked ok since installed 2 years back.
Recent issue with circuit tripping.
Sparky identified faulty wiring in the isolator switch, switch replaced.
Sparky has advised it should be on a 32A RCBO.

Checking the shower installation manual, it states 40/45A MCB for their 9.5kW model, however if running on a 6mm cable they further state circuit protection should be 32A. So that's why he's suggesting a 32A RCBO?

I'm assuming best practice would have been 10mm cable, however shower was installed by plumber as a replacement during refurb so he'll just have used the existing cable.

If the 6mm cable's to remain in-situ, do you agree re dropping to 32A RCBO?

 

[pete01]

How's longs the 6mms run roughly and do you think it's has any insulation covering it?

 

[pete01]

That's 20m clipped direct (no insulation but can be in the wall)

 

[SUNRAY]

TLCcalculator goes to 10.5KW and 34m clipped direct

However thatchanges very quickly if insulation is involved

 

[diy_fun_uk]

How's longs the 6mms run roughly and do you think it's has any insulation covering it?

At a rough guess I'd say 5m, 6m max. The shower room (not overly big) is directly adjacent to the cupboard housing the fuse box. I'm not sure about the installation aspect tbh, however I reckon the cable probably just runs through the wall or indeed maybe even under the shower tray.

 

[pete01]

At a rough guess I'd say 5m, 6m max. The shower room (not overly big) is directly adjacent to the cupboard housing the fuse box. I'm not sure about the installation aspect tbh, however I reckon the cable probably just runs through the wall or indeed maybe even under the shower tray.

From what you are saying I would say 6mm on a 40 amp is fine.

 

[SUNRAY]

From what you are saying I would say 6mm on a 40 amp is fine.

That is my gut feeling and certainly is the case for clipped direct with no thermal insulation right up to 10.5KW and 34m of cable.

The moment any insulation is added into the calculator (I use https://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html on-line calculator) it gives 10 or 16mm for anything over 8KW

 

[EFLImpudence]

Whatever the problem, and especially for the RCBO tripping, just fitting a 32A RCBO instead is not a solution.

 

[morqthana]

Sparky has advised it should be on a 32A RCBO.

Checking the shower installation manual, it states 40/45A MCB for their 9.5kW model, however if running on a 6mm cable they further state circuit protection should be 32A.

Can neither the sparky nor the manufacturer do the sums which show that 32A is not enough for a 9.5kW shower?

 

[Jurassicspark]

Sparky identified faulty wiring in the isolator switch, switch replaced.

Did he know what caused the real problem?

Did he say "faulty wiring" or did he say the switch was faulty or were the connections incorrect? Neither except the former probably caused the issue.

Sparky has advised it should be on a 32A RCBO.

9500/240 = approximately 40A.

do you agree re dropping to 32A RCBO

Can you screenshot where it says that on the instructional manual please?

 

[pete01]

Did he know what caused the real problem?

Loose connection in the pull cord/switch by the sounds of it

 

[Jurassicspark]

Checking the shower installation manual, it states 40/45A MCB for their 9.5kW model, however if running on a 6mm cable they further state circuit protection should be 32A.

Are they expecting people to take short showers to avoid the 32A MCB tripping?

 

[diy_fun_uk]

Hi all

Thanks for further replies. Yes, he advised the tripping was due to poor installation of the isolator switch. Cables partially burnt out due to poor connections, not all of the live cores terminated.

The shower manufacturer doesn't recommend 6mm with 32A coupled to a 9.5kW model. Indeed, they state it's best to use a minimum of 10mm if the cable is likely to run in any situation that isn't ideal.

However they do state 'The current carrying capacity of the cable must be at least that of the shower circuit protection (see Table B).'

Essentially, assuming the issue has been fixed with the replacement and properly wired isolator switch, I would like to know if it's advisable to have the 32A RCBO fitted or just leave the 40A? This assumes 6mm cable left in-situ.

Although I'd need to check, I am doubtful any form of cable insulation has been used.

 

[EFLImpudence]

Checking the shower installation manual, it states 40/45A MCB for their 9.5kW model,

Exactly.

however if running on a 6mm cable they further state circuit protection should be 32A. So that's why he's suggesting a 32A RCBO?

Yes, but that doesn't mean you can have that if the shower is 40A.

 

[pete01]

From what you are saying I would say 6mm on a 40 amp is fine.

I'll stick with what I said above....in your case you have proof its fine as its been fine for 2 years.