Installation of an electric shower

C.R.A.Z.Y · 30 Jun 2016 at 21:25

If the supply to the shower isn't RCD protected then I would highly recommend upgrading to RCD/RCBO to bring it up too 17th Ed. Regs and for piece of mind.

It's always good practice to go with a belt & braces approach when dealing with electrics, especially when water is involved. Supplementary bonding and RCD would give you dual disconnect routes, super safe shower time!

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AS_Platinum · 30 Jun 2016 at 21:26

a1ex2001 said:
You are correct technically as this isn't a like for like swap it is part p notifiable, personally I wouldn't have a problem doing it if it was really straightforward but as your getting into lengthening cables and your unsure of the size of the current cable I'd call a pro to be sure. It's unlikely but Under spec cabling could burn your house down!

I agree, if the OP feels he is competent to do the job, then by all means go for it.
I suspect the cable is 10mm already, seeing as the existing shower was an 8K unit and the MCB is rated at 40A.

AS_Platinum · 30 Jun 2016 at 21:30

C.R.A.Z.Y said:
If the supply to the shower isn't RCD protected then I would highly recommend upgrading to RCD/RCBO to bring it up too 17th Ed. Regs and for piece of mind.

It's always good practice to go with a belt & braces approach when dealing with electrics, especially when water is involved. Supplementary bonding and RCD would give you dual disconnect routes, super safe shower time! )

Regs don't state an RCD is required unless it is a TT installation. Follow the manufacturers instructions, most stipulate an RCD is required.

C.R.A.Z.Y · 30 Jun 2016 at 21:35

The 40A MCB will be fine for 9.8kW load (provided the cable run isn't stupidly long)
MCB's can operate for about an hour at approx 135% load before tripping so unless you have stupidly long showers it will be fine.

You need to however confirm 100% the CSA of the current cable installed, as stated 10mm is fine but if it's 6mm then increasing the load to 9.8kW's starts making things dangerous and a fire risk!! (NEVER assume the current installation is safe or correct)

C.R.A.Z.Y · 30 Jun 2016 at 21:43

AS_Platinum said:
Regs don't state an RCD is required unless it is a TT installation. Follow the manufacturers instructions, most stipulate an RCD is required.

Regulation 701.411.3.3 means that all circuits, including lighting, electric showers, heated towel rails, etc., will require RCD protection, not exceeding 30 mA.

17th Edition launched-Bathrooms - IET Electrical

AS_Platinum · 30 Jun 2016 at 22:14

C.R.A.Z.Y said:
Regulation 701.411.3.3 means that all circuits, including lighting, electric showers, heated towel rails, etc., will require RCD protection, not exceeding 30 mA.

17th Edition launched-Bathrooms - IET Electrical

Yep, you're right.

JanM · 30 Jun 2016 at 22:59

AS_Platinum said:
Can you take a photo of the cable, with a reference point. Most sparks can just look at a cable and tell what size it is.

The circuit in question is RCD protected and there is a 17th edition consumer unit installed.

I'll update when I get the specs for the cable. Posting a pic with a ruler wont be a problem but I'd rather be sure and if I can't find any text on the cable tomorrow I'll measure the strands with calipers and work out he cross section.

Beer_MonsterUK · 1 Jul 2016 at 10:29

10mm "should" be fine for a 9.8Kw shower, but it is close.

The current draw of the shower will be around 42amps, and the 10mm cable is good for around 45amps, but that is completely depending on the installation method of the cable. If it's installed above a ceiling with any insulation over 100mm or in a stud wall with insulation then it drags the carrying capacity of the cable down to around 36amps, and a larger cable is required.

From the IET.

Question
If I replace an existing electric shower with a new electric shower connected to an existing shower circuit is this notifiable work?
Answer
Even though the shower is within the zones the answer is No, provided that the shower is a like-for-like replacement.

Strictly speaking it IS notifiable, as you are increasing the loading of the circuit. I'd be changing it and be done with it. But you have to be sure of the design of the circuit.

JanM · 1 Jul 2016 at 11:07

So checked this morning, and there is no text on the cable.

Going to have to measure it manually over the weekend with calipers and do the calculation.

The cable is on a long run... exposed all the way along the cellar ceiling up the cellar stairs, to the hallway then along the stairs up the storage room and into the roof.
Quite a long run, its exposed most of the way. The long run was done most likely to keep it concealed as much as possible.

Lumeycom · 1 Jul 2016 at 19:49

Honestly dude just post a picture of it, most of us sparks will ID a cable size pretty instantly

Someone mentioned above, is the earth a single strand or more? 6mm would likely have a single strand earth where bigger would have 7 strands.

JanM · 1 Jul 2016 at 20:31

Here is a pic of it next to a ruler

AS_Platinum · 1 Jul 2016 at 22:03

JanM · 1 Jul 2016 at 22:19

Damn, yeah I thought it might be.
Whats the maximum power a 6mm cable capable of handling?
I'm not 100 percent sure but I think our old shower is 8kw or 8.5kw.

I'll contact the sparky tomorrow to get a quote to get it installed with cable and i'll
get him to put a bigger fuse in too.

Beer_MonsterUK · 1 Jul 2016 at 23:57

yup, 14x7 clips = 6mm.

Clipped direct it's max current capacity is 47 amps, but that drops to 34amps once it's enclosed in a ceiling or wall.

It was ok for an 8Kw shower which would pull 34amps, but anything larger would need a bigger cable.

JanM · 2 Jul 2016 at 09:40

Beer_MonsterUK said:
yup, 14x7 clips = 6mm.

Clipped direct it's max current capacity is 47 amps, but that drops to 34amps once it's enclosed in a ceiling or wall.

It was ok for an 8Kw shower which would pull 34amps, but anything larger would need a bigger cable.

Thanks for the information. I'll see what quote the electrician comes up with. If its too expensive to do the required conversions then i may have to exchange the shower.

Adam_151 · 2 Jul 2016 at 13:55

Beer_MonsterUK said:
Clipped direct it's max current capacity is 47 amps, but that drops to 34amps once it's enclosed in a ceiling or wall.

Its worth remembering though that the 34A is in an insuated wall or partition, i.e. a stud wall with fireglass inside. Burried under plaster on a brick or block wall would still count as clipped direct

JanM · 7 Jul 2016 at 21:10

The quote to install shower with new cable is £250.
I may have to exchange the shower for a lower rated one.
Is 8kw the maximum I can get or can get a 8.5kw one for the 6mm cable?

The cable is not enclosed the by cavity wall or insulation. In the roof its along the top of the insulation to the shower switch.

pepp77 · 7 Jul 2016 at 21:58

I was advised to go from 6mm to 10mm when I upgraded to an 8.5kw shower.

Lumeycom · 7 Jul 2016 at 22:09

Issue your going to have is the breaker size. Standard breakers go from 32A (7.36kw @ 230v) to 40A (9.2kw @ 230v).

I'd personally be uncomfortable putting a 6mm on anything bigger than a 32a unless it was genuinely in fresh air for the WHOLE run from the DB to the shower itself.

JanM · 7 Jul 2016 at 22:21

pepp77 said:
I was advised to go from 6mm to 10mm when I upgraded to an 8.5kw shower.

Arrrgg can't find any decent 8k showers.

Lumeycom said:
Issue your going to have is the breaker size. Standard breakers go from 32A (7.36kw @ 230v) to 40A (9.2kw @ 230v).

I'd personally be uncomfortable putting a 6mm on anything bigger than a 32a unless it was genuinely in fresh air for the WHOLE run from the DB to the shower itself.

I know I'm a little uncomfortable with all this but he cable is genuinely routed in fresh air bar the holes through wall and ceiling.

From the fuse board, it goes along the cellar and cellar stairs (ceiling). Into a cupboard above the cellar door. Along the hallway stairs into a store room the first floor and then along the wall of the store room into the loft. There along the celing joists onto the switch in the bathroom.