Electric showers - can this cable support ~10kW?

Participant · 18 May 2013 at 17:54

Hi all

I just removed the old electric shower in our en-suite to replace it with a spare but better one we had lying around, and skillfully managed to break the plastic inlet tube as I tightened the compression joint.

Therefore I am after a new electric shower, but I want one that will deliver reasonable flow at a reasonable temperature, something I've not yet encountered with an electric unit.

Here's the setup:

(I've just added the valve, as it spewed water all over me when I broke the tube

)

Is it possible to tell from that picture whether or not the cable can support a 9.5 - 10.5 kW electric shower? The cable run back to the RCD is fairly long, 10m at a guess. The RCD has a 40A fuse and there's an isolator switch thing in the shower room.

Thanks.

Nightglow · 18 May 2013 at 18:02

The 40amp fuse is not ok, with 10kw shower, & that cable is 10mm T&E cable rated 53amps.

If it was 6mm T&E, earth would be single strand, not multi strands.

Participant · 18 May 2013 at 18:05

Thanks Nightglow. No way to tell how cable has been installed as it's all behind walls. Is there any way to test and make sure, or is this down to the judgement of a professional? How do I tell the difference between 6mm^2 twin and earth and 10mm^2?

Nightglow · 18 May 2013 at 18:10

10.5kw shower is around 47amps @ 220volts so you might ok, but it would need a 50amp fuse.
But distance is 10mtrs, can't work out volts drop, etc, you must be getting close to a 16mm T&E 70amps cable.
I haven't got the 17th ed regs to hand, to check tables.

Other sparks on here will confirm.

HardwareGeek · 18 May 2013 at 18:12

6mm2 t+e has a 2.5mm solid core earth

10mm2 cable has a stranded earth (more than 1 core) think 7 strands 4mm2

Participant · 18 May 2013 at 18:31

Cheers guys. Excellent news. We'll just go for a 9.5 / 9/8kW unit then I think.

paintguy · 18 May 2013 at 18:32

It'll say on the cable somewhere too if you can see enough of it, but as already said the construction makes it look like 10mm²

Should be fine for your needs but I suppose I ought to add a few words of caution: We have to assume that whoever installed the cable knew what they were doing and used the most direct route. If it runs all the way around your house before snaking back towards the shower the significant extra length would de-rate it. Also if it runs through a significant amount of insulation it's rating will be reduced.

Pedantic maybe but just something to be aware of

Nightglow · 18 May 2013 at 18:37

He is very,very close to the limit for 10mm T&E cable, with length of cable, volt drop, whether cable is clipped, covered, etc.
He is looking at 16mm T&E cable for a 10.5kw shower & a 10mtr run.

Participant · 18 May 2013 at 18:42

Thanks guys. I can't pull enough of the cable out to see any printed ratings.

So are there any tests I can run to test the quality of the cable run? As there's no way to prove any of that. It's also an extended part of the house, so for all I know they connected it to 6mm^2 stuff half way to the RCD.

Or is the first I'd know of it a fire in the wall?!

JohnnyG · 18 May 2013 at 18:54

Do a visual check at the RCD to ensure that it's still 10mm there, it's unlikely to be joined to 6mm but you never know.
There are checks you can do to ensure that the 40a MCB is sufficient protection for the cable but unless you know what you're doing it's not really recommended for a DIYer.
It wouldn't cost you that much to get a sparks in to do few circuit resistance checks (Zs) and have a look at the run, it's worth it really as incorrectly installed/specified electric showers can be troublesome

Traffic_Warden · 18 May 2013 at 18:57

If it was 6mm T&E, earth would be single strand, not multi strands.

the construction makes it look like 10mm²

I don't know what sort of sparky cert's you have... But you are both talking a pile of ****...

No one can tell from that picture alone that it is 6mm or 10mm T+E for certain...

If it is in fact 10mm T+E, that will do fine for your new ~10KW shower...

Jesus some people giving out pathetic advice is cringe worthy.

*edit

* Just to add, if there is no DP switch (Pull cord type inside the bathroom/switch outside the bathroom), This will fail inspection. Never mind testing. You can't go straight from the circuit breaker to the shower like that, it's against 17th ED regs.

Nightglow · 18 May 2013 at 19:08

Traffic_Warden said:
I don't know what sort of sparky cert's you have... But you are both talking a pile of ****...

No one can tell from that picture alone that it is 6mm or 10mm T+E for certain...

If it is in fact 10mm T+E, that will do fine for your new ~10KW shower...

Jesus some people giving out pathetic advice is cringe worthy.

*edit

* Just to add, if there is no DP switch (Pull cord type inside the bathroom/switch outside the bathroom), This will fail inspection. Never mind testing. You can't go straight from the circuit breaker to the shower like that, it's against 17th ED regs.

You should know then, that the earth conductor on 6mm T&E cable is 2.5mm, whereas on 10mm T&E is 4mm stranded.

JohnnyG · 18 May 2013 at 19:09

Nightglow said:
You should know then, that the earth conductor on 6mm T&E cable is 2.5mm, whereas on 10mm T&E is 4mm stranded.

I was just going to say that.
I haven't seen a stranded CPC on 6mm harmonized colours, at all

HardwareGeek · 18 May 2013 at 19:09

Traffic_Warden said:
I don't know what sort of sparky cert's you have... But you are both talking a pile of ****...

No one can tell from that picture alone that it is 6mm or 10mm T+E for certain...

If it is in fact 10mm T+E, that will do fine for your new ~10KW shower...

Jesus some people giving out pathetic advice is cringe worthy.

*edit

* Just to add, if there is no DP switch (Pull cord type inside the bathroom/switch outside the bathroom), This will fail inspection. Never mind testing. You can't go straight from the circuit breaker to the shower like that, it's against 17th ED regs.

I know there have been some funky cables out there in the past but did they ever make 6mm t+e in new colours with a stranded earth?

Traffic_Warden · 18 May 2013 at 19:10

No, 6mm T&E cable can have either standed/non-stranded CPC.

*

Nightglow · 18 May 2013 at 19:15

Traffic_Warden said:
No, 6mm T&E cable can have either standed/non-stranded CPC.

Since when,I'm trying think back 30 years & remember whether I seen a multi strand earth on a 6mm cable, also that cable has the new harmonized colours.

JohnnyG · 18 May 2013 at 19:16

OP, just measure the outside of the insulation.
10mm will be about 17x10 & 6mm will be 13.5x7, I'm still going for the former

HardwareGeek · 18 May 2013 at 19:16

Traffic_Warden said:
No, 6mm T&E cable can have either standed/non-stranded CPC.

Not saying you are wrong but i haven't seen any, any chance of a link to explain or where it can be purchased.

Nightglow · 18 May 2013 at 19:23

JohnnyG said:
OP, just measure the outside of the insulation.
10mm will be about 17x10 & 6mm will be 13.5x7, I'm still going for the former

Someone with brains. :eek:

Traffic_Warden · 18 May 2013 at 19:24

I can't see any online, as the shops don't have independant pictures for each cable, they just use the same picture and change the price and product.

I'm not saying it doesn't look like 10mm T+E in the picture, but I don't agree with you saying it is _purely_ on the basis you think 6mm T+E only has single strand CPC.

I've seen 6mm T+E have 3strand CPC before, I didn't install it, but I've worked with it in the new colours.