Electrics for a 9.5kW Shower

[magd36]

I have had a 9.5kW shower installed for a few years now. The wire is 6mm and the MCB is 32Amp. I noticed on the shower manual that the recommended MCD is 40Amp and also strongly recommends that any shower greater that 8kW uses 10mm cable.

I don't know how risky this is. The lowest equivalent shower if I were to replace is 8.5kW which suggests that I need to rewire and replace the MCB anyway.

In summary: is 6mm, 32 Amp MCB suitable for a 9.5kW shower or an absolute no no? What about if I reduced to 8.5kW?

Opinions?

Thanks

 

[EFLImpudence]

9.5kW @ 240V is all but 40A so the MCB should be replaced with 40A subject to -

6mm² cable is fine IF clipped to surface or buried in masonry, not in conduit or thermal insulation.

I suspect the 32A MCB will be slightly overheating every time it is used (although length of time of each use is a factor) and will give up eventually.
8.5kW is still strictly speaking too much for 32A MCB.

 

[magd36]

I'll have to find the routing of the cable as it could run down between the plasterboard and the outside wall which will likely be insulated. I presume that's what you mean by thermal insulation?

Thanks again.

 

[EFLImpudence]

Yes, but it depends on whether surrounded by the insulation or not.

 

[blup]

My 8.5kw shower regularly tripped on a 6mm cable protected (at the time) by a 32 amp mcb, but if it doesn't on yours, I personally wouldn't worry unduly. I'd be more concerned if there was no RCD protection.

Blup

 

[EFLImpudence]

The cable has nothing to do with it.

 

[Harry Bloomfield]

My 9.5Kw has run on 6mm 32amp for a decade and without issues. The cable is installed either on the surface, in the floor or behind plasterboard and is a fairly short run. The shower, unlike it's predecessor, is triac output controlled for precise temperature, so it will not be running flat out constantly and our showers are quick ones. I have checked and there is no noticeable heating in the cable or the MCB, even with extended use.

I did initially think to upgrade it, then decided it wasn't worth the effort.

 

[sparkwright]

To the op: Out of interest, what make of consumer unit do you have? And do you have RCD protection?

 

[magd36]

Yes it has RCD protection. It's an MK Sentry unit.

Thanks

 

[magd36]

The cable has nothing to do with it.

Sorry if this is a stupid question but I imagined the cable would be critical in the sense that if it's too narrow and the MCB has a high rating, it would potentially melt/breakdown before it trips? i.e. I presumed you would not put a 45A MCB on a 6mm cable.

Thanks

 

[magd36]

To the op: Out of interest, what make of consumer unit do you have? And do you have RCD protection?

Yes it has RCD protection. It's an MK Sentry unit.

Thanks

 

[sparkwright]

Sorry if this is a stupid question but I imagined the cable would be critical in the sense that if it's too narrow and the MCB has a high rating, it would potentially melt/breakdown before it trips? i.e. I presumed you would not put a 45A MCB on a 6mm cable.

Thanks

Depending on how it's installed, 6mm2 can be good for 47A. 6mm2 is often protected by a 45A MCB, when needs be. Not all manufacturers make 45A MCBs.

 

[EFLImpudence]

Sorry if this is a stupid question but I imagined the cable would be critical in the sense that if it's too narrow and the MCB has a high rating, it would potentially melt/breakdown before it trips? i.e. I presumed you would not put a 45A MCB on a 6mm cable.

Yes, that is correct but the cable is not too small.

It can take 47A clipped direct or buried in masonry.

My 8.5kw shower regularly tripped on a 6mm cable protected (at the time) by a 32 amp mcb, but if it doesn't on yours, I personally wouldn't worry unduly. I'd be more concerned if there was no RCD protection.
Blup

The cable has nothing to do with the MCB tripping

 

[magd36]

Depending on how it's installed, 6mm2 can be good for 47A. 6mm2 is often protected by a 45A MCB, when needs be. Not all manufacturers make 45A MCBs.

Yes, that is correct but the cable is not too small.

It can take 47A clipped direct or buried in masonry.

Thanks, I understand. Why then, would a 10mm2 cable be recommend with a 40A trip (in the shower manual)?

 

[flameport]

Why then, would a 10mm2 cable be recommend with a 40A trip (in the shower manual)?

Perhaps they are assuming most cables will be installed in less than ideal conditions such as under loft insulation or similar.
Or those that wrote the manual were unaware of cable ratings.