Shower

[keenamateur]

Hello

I want to fit a new electric shower

the existing shower is 7kw and on a 32 amp MCB

the cable is 6mm - I've been informed

what is the max size shower I can fit?I would like to get a 9.5 Kw

cable length is about 8m and runs through a stud wall insulated

The max size mcb I can get for the fuseboard is either a 40 or 50 amp

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Thanks

 

[comms]

No you want 10mm for a 9.5Kw shower.
Does the cable run for it's full 8mtrs in the insulated wall ?

 

[Softus]

The cable must be de-rated to 32A, which is enough for a shower rated at 7.68kW (at 240V).

 

[ricicle]

Hello,
Looks like a problem as 6mm² is rated at 46A clipped direct.You have said that the cable runs in an insulated wall so it is a reasonable assumption that it is totally enclosed in insulation for more than 0.5 metres.This unfortunately reduces the current carrying capacity of 6mm² to half (ie 23A) so you have a situation that is not correct with the existing set -up, let alone trying to increase the current drawn on the circuit.
I suggest you seek the services of a competant electrician to sort this out for you as the cable route needs looking at, as does confirmation of it's CSA and suitability of the consumer unit for such an addition.
The existing installation could cause cable overheating so I suggest you treat this as a matter of urgency.

 

[keenamateur]

thanks for a quick reply

no goes under floor then goes up about 2.5 M in stud

ta

 

[ricicle]

thanks for a quick reply

no goes under floor then goes up about 2.5 M in stud

ta

***See my post above***

 

[letigre]

Hello,
Looks like a problem as 6mm² is rated at 46A clipped direct.You have said that the cable runs in an insulated wall so it is a reasonable assumption that it is totally enclosed in insulation for more than 0.5 metres.This unfortunately reduces the current carrying capacity of 6mm² to half (ie 23A) so you have a situation that is not correct with the existing set -up, let alone trying to increase the current drawn on the circuit.
I suggest you seek the services of a competant electrician to sort this out for you as the cable route needs looking at, as does confirmation of it's CSA and suitability of the consumer unit for such an addition.
The existing installation could cause cable overheating so I suggest you treat this as a matter of urgency.

As every new home and older ones are now well insulated - and its inevitable that cables will pass through this insualtion

do all cables get derated by 50% ?

and whats the max kw shower that can be provided on the above set up with 10mm cable.

 

[Softus]

As every new home and older ones are now well insulated - and its inevitable that cables will pass through this insualtion

I disagree. However, if it turns out that your right, it influences neither the regulations nor the importance of complying with them.

do all cables get derated by 50% ?

All cables that are subject to de-rating factors, but not the cables that aren't.

and whats the max kw shower that can be provided on the above set up with 10mm cable.

10.32kW at 240V.

 

[davelx]

Don't forget that the 50% derate applies to cable that is BURIED in insulation - ie surrounded on all sides. If one side is in contact with the plasterboard, that is a different matter - it becomes installation method 15 table 4D5A pg 228, in which case the 32A MCB is fine, since 6mm T+E under IM15 is rated 35A

Could the OP be more precise about how the cable is run in the wall?

 

[keenamateur]

Hi

Thanks to everyone for their knowledge

re how cable is run in wall..................

there is a 75mm stud with plasterboard on both sides, as with all bathroom walls it is insulated with rockwool.

As has been noted it probably touches one side of the plasterboard but I can't fully see this, I just know its insulated.

Can I fit a 9Kw shower? on a 40 mcb?

Thanks

 

[ricicle]

No!

If one side is in contact with the plasterboard, that is a different matter - it becomes installation method 15 table 4D5A pg 228, in which case the 32A MCB is fine, since 6mm T+E under IM15 is rated 35A

You cannot fit a bigger protective device than the corrected rating of the cable.I'm afraid you're stuck with 32A (7.68kW @ 240V)

 

[electronicsuk]

No, even the old shower is likely to be of a higher rating than anything that should have been placed on that circuit, unless of course the cable is only insulated on one side. Under no circumstances with your current setup are you likely to achieve 9kw.

Damn, beaten!

 

[keenamateur]

thank you to all