Bulk Workwear - Clothing Suppliers for the Whole Forum Network
This official sponsor may provide discounts for members

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

Reaction score
4
Welcome to ElectriciansForums.net - The American Electrical Advice Forum
Head straight to the main forums to chat by click here:  American Electrical Advice Forum

Hi All,

We have just had an electrical test done and have been told that our 8.5kW shower is too powerful for the 6mm cable. We have been told it should be replaced with a 7.5kW maximum.
I was under the impression and stand to be corrected that an 8.5kw would be fine for that cable as long as the run didn't exceed 18m. It doesn't. The run is about 6m maximum.
Can anyone advise please? The shower was actually installed by an electrician who stated that it was fine.
Cheers.
Paul
 

James

-
Mentor
Esteemed
Arms
Supporter
Patron
Reaction score
4,076
Hi All,

We have just had an electrical test done and have been told that our 8.5kW shower is too powerful for the 6mm cable. We have been told it should be replaced with a 7.5kW maximum.
I was under the impression and stand to be corrected that an 8.5kw would be fine for that cable as long as the run didn't exceed 18m. It doesn't. The run is about 6m maximum.
Can anyone advise please? The shower was actually installed by an electrician who stated that it was fine.
Cheers.
Paul
8.5kw is approx 37A
6mm is good for between 30 and 46A depending on the installation method.

I would ask the inspector to show you his calculations and assumptions.
 

brianmoooore

-
Esteemed
Arms
Reaction score
1,580
The length of the cable is fine. It's what the cable passes through on the way is the potential problem - contact with thermal insulation can reduce its current carrying capacity considerably.
Then there's the shower. 8.5kW at what voltage? Is this stated at 240 volts or 230? The declared UK mains voltage has been 230 for some time, but some shower manufacturers still state the power at 240 volts, because it looks better. Often the rated power at 230 volts is shown in much smaller print, although it's the one that matters.
 

loz2754

-
Esteemed
Arms
Reaction score
2,015
Hi.
As James says, it depends on the installation method of the cable run. If the cable is in an insulated wall, or covered with insulation in a loft, or both, the cable size can jump to 10mm² or even 16mm². This is to allow for dissipation of heat generated, which is severely hindered when in insulating material.
 
Reaction score
4
Thank you James for your reply. I thought it was ok (I used to do my own electrics until lack of being qualified forced me to stop. I always got a qualified electrician to check over my work) and had confidence in the chap that fitted it.
I will ask.
Regards,
Paul
8.5kw is approx 37A
6mm is good for between 30 and 46A depending on the installation method.

I would ask the inspector to show you his calculations and assumptions.
 
Reaction score
4
Hi.
As James says, it depends on the installation method of the cable run. If the cable is in an insulated wall, or covered with insulation in a loft, or both, the cable size can jump to 10mm² or even 16mm². This is to allow for dissipation of heat generated, which is severely hindered when in insulating material.
Thank you Ioz. As far as I can recall, the cable runs from the consumer unit under the stairs and then up the wall to the pull switch. There would be a run of no more than 0.5m under the loft insulation before it goes down behind the wall of the shower.
We have an en-suite with a 8.5kW as well and we were told that must be changed. The cable run is probably 3m longer, but is in 10mm. However, there is a slight problem there, which has only just been ascertained. The 10mm runs to the pull switch, then the electrician ran 6mm from there to the shower for some reason. I can only imagine he ran out of cable as it wasn't what was asked or paid for!
I would imagine that shower would also be fine with an 8.5kW?

Regards,

Paul
 

loz2754

-
Esteemed
Arms
Reaction score
2,015
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.
 

Dave OCD

-
Mentor
Esteemed
Arms
Reaction score
5,609
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.
 

James

-
Mentor
Esteemed
Arms
Supporter
Patron
Reaction score
4,076
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!!
 
Reaction score
4
The length of the cable is fine. It's what the cable passes through on the way is the potential problem - contact with thermal insulation can reduce its current carrying capacity considerably.
Then there's the shower. 8.5kW at what voltage? Is this stated at 240 volts or 230? The declared UK mains voltage has been 230 for some time, but some shower manufacturers still state the power at 240 volts, because it looks better. Often the rated power at 230 volts is shown in much smaller print, although it's the one that matters.
Thank you Brian. I'd not realised that.

What difference would the 230 or 240 volts make?

Paul
 

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

Electrical Forum

Welcome to the Electrical Forum at ElectriciansForums.net. The friendliest electrical forum online. General electrical questions and answers can be found in the electrical forum.
Top