8.5kw Shower on a 6.0mm cable

[Sb8389]

Hi guys,
want your opinion on a issue I have found while changing a consumer unit today.
I came across the shower wired in 6.0mm on a 32amp MCB (8.5KW). I know this will draw just over 35amps and could do with being upgraded to a 40amp MCB, but checking the install of the cable it is going through cavity full of insulation and then through the loft covered in insulation.
i know that the protective device will be overloaded but would you say that this would be a risk to leave on a 32amp MCB and would you be able to tell me how long it would take for the MCB to trip at 35amps as I don't have a regs book to hand to check the time current curve graph.
if you need any more info let us know.

thanks.

 

[Simonslimline]

Remind me which regulation number it is which says that something which has worked for 9 years is automatically considered correct and other regulations can be ignored?

I never said it was correct or compliant. But to be honest It was installed by the housing associations so called sparks so i wouldn't expect it to be to be honest.

My point was simply that it wont trip while taking a shower unless your in there for a very very very long time.

 

[HappyHippyDad]

Hi guys,
want your opinion on a issue I have found while changing a consumer unit today.
I came across the shower wired in 6.0mm on a 32amp MCB (8.5KW). I know this will draw just over 35amps and could do with being upgraded to a 40amp MCB, but checking the install of the cable it is going through cavity full of insulation and then through the loft covered in insulation.
i know that the protective device will be overloaded but would you say that this would be a risk to leave on a 32amp MCB and would you be able to tell me how long it would take for the MCB to trip at 35amps as I don't have a regs book to hand to check the time current curve graph.
if you need any more info let us know.

thanks.

This is a interesting thread! I wonder how many times a consumer unit is changed that has an 8.5KW shower on a 6mm, quite often I expect. A 6mm cable is fine for 8.5KW shower (if clipped direct), but when we change a consumer unit how are we to tell if the walls have insulation in them (ref method 102) and if the cable is not touching the inner wall (ref method 103)?

If you have these details SB then I cant really see how you can reconnect back up given that the CCC of the cable is going to be anywhere from 23.5A (ref method 103) to 34A (ref method 100). Although if it is ref method 100 (34A) then even though a 32A MCB will not trip at 34A I would have thought the CCC of cable (with regards ref method) is designed with this in mind.

 

[Sb8389]

I see your point happyhippydad but to determine how it's installed throughout its length can be difficult in a lot situations.
it was installed on 30amp before and there is no evidence of overheating to the cable. I know that don't confirm its right to leave it but does that mean we have say to the customer it will need rewiring when we come across this situation when we can't determine its installation method.

 

[davesparks]

It's also rated for an operating current of 35A for a specific duration of time. I guess our definition of 'overload' might be differing slightly.

Operating current was a poor choice of words in this case.
I don't think it will be rated to operate at 35A at all.

 

[davesparks]

Hi davesparks,
would you say the circuit needs rewiring then,I know the circuit has being designed incorrectly but does it mean it's a risk or just not compliant to regs and can be just noted on cert.

it may just need the correct mcb to be fitted for the load

 

[HappyHippyDad]

it may just need the correct mcb to be fitted for the load

Not quite sure what you are getting at here? The load is 37A. What MCB would you suggest to make this situation ok?

 

[PEG]

....Is anyone going to clamp this,and have at least one known factor? :winkiss:

 

[davesparks]

Not quite sure what you are getting at here? The load is 37A. What MCB would you suggest to make this situation ok?

How did you get to 37A from an 8.5kW shower?
A 40A mcb would be correct for the load

 

[HappyHippyDad]

I see your point happyhippydad but to determine how it's installed throughout its length can be difficult in a lot situations.
it was installed on 30amp before and there is no evidence of overheating to the cable. I know that don't confirm its right to leave it but does that mean we have say to the customer it will need rewiring when we come across this situation when we can't determine its installation method.

Very true SB! But you've said in your post that its covered in insulation, so you have determined how its installed. If its got >100mm of insulation over it in the loft which is quite feasible then its CCC goes down to 27! I suppose you could clamp it and see how much it is drawing and perhaps use a 25A MCB? But you could start getting some tripping!

 

[davesparks]

Very true SB! But you've said in your post that its covered in insulation, so you have determined how its installed. If its got >100mm of insulation over it in the loft which is quite feasible then its CCC goes down to 27! I suppose you could clamp it and see how much it is drawing and perhaps use a 25A MCB? But you could start getting some tripping!

How on earth would a lower rated mcb help the situation?
The mcb does not determine the load current!

 

[Sb8389]

Very true SB! But you've said in your post that its covered in insulation, so you have determined how its installed. If its got >100mm of insulation over it in the loft which is quite feasible then its CCC goes down to 27! I suppose you could clamp it and see how much it is drawing and perhaps use a 25A MCB? But you could start getting some tripping![/Q

i will clamp it tomorrow and see what its drawing and give myself a clearer idea of what we are dealing with.

 

[Lucien Nunes]

How on earth would a lower rated mcb help the situation?

It converts a 'possible cable overheating' risk into a 'shower user jumps out of cold shower and goes to reset MCB with wet hands' risk. I've lost track, was this thread about solving a problem or creating one?

 

[HappyHippyDad]

How did you get to 37A from an 8.5kW shower?
A 40A mcb would be correct for the load

I think you may be trying to push me towards saying the obvious here :smile5:

How on earth would a lower rated mcb help the situation?
The mcb does not determine the load current!

The OP has stated the reference method. i.e 'covered in insulation', so the CCC of the cable is reduced, would you suggest increasing the MCB?

 

[Marvo]

Operating current was a poor choice of words in this case.
I don't think it will be rated to operate at 35A at all.

According to the published curves all MCB's are designed to be operated above their In and perform to the predictable disconnect times which in this case, given it's a fixed load and a disconnect time far in excess of the duration of use, will not be of consequence. I think it's a stretch to say this particular circuit is overloaded just because the load is 1.16 times the In and assuming the cable size is appropriate.

 

[micknew]

Seems like the op is looking for reasons to ignore the regs.
Surely they must be adhered to?
If not throw the rule book away lol.