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Hi guys I have been asked to fit new shower and run new cable for it too, looking at regs book it would have to be reference method 103, which for 8.5kw shower would mean 16mm cable, can terminals in the shower take 16mm and the terminals in the isolator? I have tried looking for different cable routes but the board is downstairs and the bathroom is upstairs. 10mm is what is in at the moment. I don't usually do domestic electrical work so any advice would be great. I just thought 16mm was a bit overly for 8.5kw shower.
 
OP
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I just used one of those online volt drop calculator things and they come up with 16mm also. just I was looking at the regulations book for 10mm ccc and noticed with method 103 that it would be rated to 32 amps therefore I would have to go to 16 as the shower is 35.4 amps. I was just going to run 10mm but I guess I should go 16 to be in line with regs. I cant see any other different cable route. I have spoken to other electricians and they have said to just run 10mm but I would rather be safe than sorry. I usually work offshore so this domestic side is something im not really familiar with. thanks for your help
 

buzzlightyear

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just used one of those online volt drop calculator things and they come up with 16mm also. just I was looking at the regulations book for 10mm ccc and noticed with method 103 that it would be rated to 32 amps therefore I would have to go to 16 as the shower is 35.4 amps. I was just going to run 10mm but I guess I should go 16 to be in line with regs. I cant see any other different cable route. I have spoken to other electricians and they have said to just run 10mm but I would rather be safe than sorry. I usually work offshore so this domestic side is something im not really familiar with. thanks for your help
Rule with a big thumb stick in 10mm
For a up grade of shower.
 

Pete999

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Hi guys I have been asked to fit new shower and run new cable for it too, looking at regs book it would have to be reference method 103, which for 8.5kw shower would mean 16mm cable, can terminals in the shower take 16mm and the terminals in the isolator? I have tried looking for different cable routes but the board is downstairs and the bathroom is upstairs. 10mm is what is in at the moment. I don't usually do domestic electrical work so any advice would be great. I just thought 16mm was a bit overly for 8.5kw shower.
You don't mention in your post the length of the run of this circuit.
 

LastManOnline

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Hi guys I have been asked to fit new shower and run new cable for it too, looking at regs book it would have to be reference method 103, which for 8.5kw shower would mean 16mm cable, can terminals in the shower take 16mm and the terminals in the isolator? I have tried looking for different cable routes but the board is downstairs and the bathroom is upstairs. 10mm is what is in at the moment. I don't usually do domestic electrical work so any advice would be great. I just thought 16mm was a bit overly for 8.5kw shower.
Well there is a little bit of history in the making here for me. An 8.5 kW shower wired in 16mm?.Am really curious to know the installation conditions for this one. I must assume it is immersed in insulation and on the top floor of a 3 story structure?
 

LastManOnline

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And theystill probably running fine
Yes. I posed a question on a different forum as to whether any spark had come across a heat damaged 6mm cable supplying an electric shower.?. No one had. I personally never have. House I, m currently renting has our shower wired in 4mm (lying on top of, not under insulation) .To date every shower repair I have personally carried out has always been either a heat damaged pull switch or a heat damaged rcbo
 

Grant1987

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Yes. I posed a question on a different forum as to whether any spark had come across a heat damaged 6mm cable supplying an electric shower.?. No one had. I personally never have. House I, m currently renting has our shower wired in 4mm (lying on top of, not under insulation) .To date every shower repair I have personally carried out has always been either a heat damaged pull switch or a heat damaged rcbo
It’s bad practice though isn’t it, when carrying out EICR’S I code it as a C3 with no thermal effects and downgrade mcb to 32A rather than the 40A installed. If I’m asked to replace faulty shower which is 8.5kw or above on a 6mm cable I will renew cable with 10mm it’s the right thing to do isn’t it.
 

LastManOnline

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It’s bad practice though isn’t it, when carrying out EICR’S I code it as a C3 with no thermal effects and downgrade mcb to 32A rather than the 40A installed. If I’m asked to replace faulty shower which is 8.5kw or above on a 6mm cable I will renew cable with 10mm it’s the right thing to do isn’t it.
Yes it is. Of course 4mm would, nt meet any parameters and of I,m not suggesting it be used. What I am suggesting is there might be reasons to reconsider how we calculate cable size for loads like electric showers which in reality tend to be used a lot more sparingly than perhaps other loads like heat pumps which have more constant use . My shower is an 8.5 kW wired in 4 mm. The OP is talking about installing the same shower in 16mm.Are we missing something?
I regularly see 6mm covered in insulation in family homes where the shower is used 4 to 5 times a day without no obvious side effects
 

Grant1987

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Yes it is. Of course 4mm would, nt meet any parameters and of I,m not suggesting it be used. What I am suggesting is there might be reasons to reconsider how we calculate cable size for loads like electric showers which in reality tend to be used a lot more sparingly than perhaps other loads like heat pumps which have more constant use . My shower is an 8.5 kW wired in 4 mm. The OP is talking about installing the same shower in 16mm.Are we missing something?
I regularly see 6mm covered in insulation in family homes where the shower is used 4 to 5 times a day without no obvious side effects
Yes fair enough I deviated from the OP using 16mm is overkill isn’t it. Yea it’s for sustained periods which would cause the problems isn’t it tbh a shower is not constantly run so the chances of damage are minimal but I just like to stick to my beliefs and prefer 10mm on shower circuits gives me peace of mind.
 

Welchyboy1

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Yes. I posed a question on a different forum as to whether any spark had come across a heat damaged 6mm cable supplying an electric shower.?. No one had. I personally never have. House I, m currently renting has our shower wired in 4mm (lying on top of, not under insulation) .To date every shower repair I have personally carried out has always been either a heat damaged pull switch or a heat damaged rcbo
Nope never
Always the pull switch connections or a point of termination at shower/CU thats loose
Ive seen a few 6mm/10.5KW/45A mcb combinations that had obviously been in service for years with no issues

Unless its a special situation i always use 10mm standard for showers now
Notsure i would attempt to use 16mm tho, thats a brave man there!
 

LastManOnline

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Nope never
Always the pull switch connections or a point of termination at shower/CU thats loose
Ive seen a few 6mm/10.5KW/45A mcb combinations that had obviously been in service for years with no issues

Unless its a special situation i always use 10mm standard for showers now
Notsure i would attempt to use 16mm tho, thats a brave man there!
I appreciate that 10mm is becoming the new norm. Makes sense long term. It would also be helpful if plumbers refuse to install 10.5 kW showers before first checking the size of the existing supply.
 

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