Discuss What kW shower? in the Electrical Forum area at ElectriciansForums.net

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Put it this way, if it was in my house, I would be completely unconcerned.

however, on a public forum, I should point out that without inspection of the cable run it is impossible to give a definitive answer on the capability of the cable to withstand the load for any duration.

i have seen similar loads on 4mm cable and had been there for years with no problems although I would point out that 4mm is pushing your luck!!
We were unconcerned until the inspection! We had a complete rewire around 24 years ago, when we bought the house. Other things highlighted, due to regs changes, which are understandable are that we don't have a fireproof consumer unit and the bathroom lighting doesn't conform. We will get the things sorted out, it's just that no reason was given for the shower change. I have asked them to explain their reasoning behind it.

Paul
 
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I know regulations and good design should be adhered to but there must be hundreds of thousands of 8.5kW showers running happily on 6mm cable throughout the country - some with much longer runs than the example on this thread. After all we're not looking at continuous current demand with a shower, even a teenager would struggle to be in there for 20 minutes for their monthly shower. 😁
I think this is just another example of the attitude that's out there with some of these 'inspectors' now , doesn't does any of us any favours.
This is what I thought.

Paul
 
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Table 52.2 - cable surrounded by thermal insulation:

Length in insulation 50mm derate cable by 0.88.
Length in insulation 100mm derate cable by 0.78.
Length in insulation 200mm derate cable by 0.63.
Length in insulation 400mm derate cable by 0.51.

So a cable normally capable of carrying 47 amps clipped direct is reduced to 41 amps for 50mm of insulation.
And 36 amps for 100mm.
And 29 amps for 200mm.
And 23 amps for 400mm.

These are some of the calculations that need to be made when designing a circuit.
These are also the calculations that all too often are not made when designing a circuit.

Having said that, your shower may well be fine and not cause any problems. But there is always an associated risk when shortcuts are taken.
Ioz, that makes it very understandable. Cheers.
Paul
 

Dartlec

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We were unconcerned until the inspection! We had a complete rewire around 24 years ago, when we bought the house. Other things highlighted, due to regs changes, which are understandable are that we don't have a fireproof consumer unit and the bathroom lighting doesn't conform. We will get the things sorted out, it's just that no reason was given for the shower change. I have asked them to explain their reasoning behind it.

Paul
Hopefully the "fireproof" consumer unit was noted only as a C3 and not required to be changed, not as a C2? There is no requirement to replace otherwise perfectly serviceable consumer units to meet current regulations regarding non-combustible construction.

The bathroom lights issue (presumably lack of RCD protection) may well need resolving, though that is often possible without a full Consumer Unit change.

With any inspection like this, I would always ask for an explanation of their reasoning (backed up by guidance or regulations) if it is not clear from the document they have provided - and consider getting alternative quotes for remedial work.

If you can remove any identifying information from the EICR and post it here, people should be able to give you a good idea as to whether the noted issues are over officious, unreasonable, or just a matter of judgement.

I assume this is a rented property now?
 

brianmoooore

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What difference would the 230 or 240 volts make?

Paul
If it is rated as 8.5kW at 240 volt, it should be treated as 7.8kW for all calculations. Current, for design purposes is a fraction under 34A.
Did you say that you have two 8.5kW electric showers? If so, then that could be a problem for an EICR. There is no diversity allowable for an instantaneous water heater, so they have to be assumed to be continuously on for calculation purposes. 2 x 8.5kW = 17kW, which overloads a normal 15kW domestic supply without taking any other loads into consideration.
 
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If it is rated as 8.5kW at 240 volt, it should be treated as 7.8kW for all calculations. Current, for design purposes is a fraction under 34A.
Did you say that you have two 8.5kW electric showers? If so, then that could be a problem for an EICR. There is no diversity allowable for an instantaneous water heater, so they have to be assumed to be continuously on for calculation purposes. 2 x 8.5kW = 17kW, which overloads a normal 15kW domestic supply without taking any other loads into consideration.
That is interesting. The overload question doesn't appear to have been raised. There is also an electric cooker and an immersion heater in the water tank should the boiler stop working.
I do know that the original electrician was an Inspector for the local electricity board at the time and he'd said that our supply wasn't enough (a 1928 built house) and arranged for it to be increased. I was at the house when a new cable was installed from the street.
 
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Hello Dartlec,

Hopefully the "fireproof" consumer unit was noted only as a C3 and not required to be changed, not as a C2? There is no requirement to replace otherwise perfectly serviceable consumer units to meet current regulations regarding non-combustible construction.

The bathroom lights issue (presumably lack of RCD protection) may well need resolving, though that is often possible without a full Consumer Unit change.

With any inspection like this, I would always ask for an explanation of their reasoning (backed up by guidance or regulations) if it is not clear from the document they have provided - and consider getting alternative quotes for remedial work.

If you can remove any identifying information from the EICR and post it here, people should be able to give you a good idea as to whether the noted issues are over officious, unreasonable, or just a matter of judgement.

I assume this is a rented property now?
Thanks for the reply. Yes it is a rented property now. I'll see what I can do about the report.
Paul
 

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