OK, so when I bought the shower, it specced 6mm sq cable.
Sadly, it eats ceiling switches and I now think I need to go up to 10 sq mm.
I shall come out from behind the consumer unit into plastic conduit and run single 10 sq mm cables up the outside wall and in through the soffit.


Questions:


What size earth conductor? They always seem smaller in twin and earth.
Is 25 mm conduit going to be OK?


Any comments?


My reason for doing it like this is that dragging a new 10 sq mm twin and earth right through the house isn't practical.


However...I DO have two 6 sq mm cables, one not used. What's to stop me using both doubled up to produce 12 sq mm?

 

Nothing really, just not good practice ,but current rating it exceeds 10mm. The practical issue is making good connections with 2 sets of cables. A good crimping tool would be useful.

 

The thickness of the cable is not the decisive factor, the current rating is the important part. I'm surprised they would specify a cable diameter rather than a current rating! Not all 6mm cables are equal!

What do you mean with it eating ceiling switches? Are the switches you're using rated high enough for the current? If it's a pull cord type switch, they are often designed for lighting and not for power showers.

 

I read up on this a while back as I too went through a couple of ceiling pull switches, the last one of which stank after having the shower running for about 10 minutes.

There were a lot of factors to consider if installing new cabling, but two that I recall was running the cable inside containment, and distance were critical to whether 6mm or 10mm were necessary for a 9.5KW shower; it made reference to de-rating factors, which I think are things which have a negative impact on the design properties of the cable - things like loft insulation around the cable, runs inside walls or continment.

There was some good info from an electrician who had tested a lot of showers, and stated that none he had ever tested drew the current that would be expected if running at the power claimed by the manufacturer. I am pretty sure he demonstrated that where installation conditions were favourable (clipped direct and clear of insulation) 6mm CSA cable would be suitable for all but the most powerful showers (over 10KW), but in new installations, 10mm CSA cable had been installed to future proof things.

I took the old switch out, replaced it (think it was MK rated at 60A), cut back and remade the connections, and made sure they were well secured. I think it was a loose connection that was causing the terminal in the switch to overheat. 6 months down the line and all is well.

Goes without saying, but I'll say it anyway, I am not an electrician.

 

Using hager genuine double pole shower switches supplied from an electrical wholesaler.


They just stop working, I think the contacts are burned.


This last one has seen the supply wire with melted insulation and welded itself into the terminal, so that I had to snip it off. I cannot remove the terminal screw either. I might send it to Hager for their comments.

 

Use a higher rated double pole switch and ensure good secure connection. Or Rewire to have wall switch outside of shower room

 

Sounds like the switches you're using are underrated.


If the cable was the problem, the whole cable would overheat with insulation melting at the weakest point, usually where you have a sharp bend in the cable.


I wouldn't really be happy with a pull cord switch for a shower. You really want a high power insulated cut-off switch similar to what you have on your oven. As said above, mount outside the bathroom or at least at a lower level where there is less steam/moisture.

 

The Hager switches are designed for shower installations, ceiling pull in case of wet hands, and rated at 60A.
A high power switch in the same room would be illegal.


I'm thinking of using BOTH 6 sq mm cables into a dp henley block (???) and using 10 sq mm from there to switch. I don't want the conduit outside the house.

 

Whats the actual power rating of the shower?

You need to work out the worst case current rating => C = P / V Voltage in the EU is standardised as 230V +/- 10%, so in the worst case your voltage could be as low as 207V!


Do you have a circuit breaker on the shower circuit? You should have a lower rated breaker/fuse than the lowest rated component - in your case probably the switch! If your switch is 60A, then you'd probably want a 50A fuse/breaker.


If you're getting a lot of moisture in the switch, then you'll get more arcing on the contacts which could cause the switch to fail. I'm really not a big fan of mounting switches on the roof in a bathroom.

 

We have cable ( large) runnning up to 63A 30mA RCD and then onwards from there through Aquapanel to the shower unit Mira 8,5 ( stop/start on the unit )


Presumably though his is running off main supply water

 

Running off main water supply, yes, although our water pressure is comically low, and, as we are tee'd off another supply, and it "just" meets the minimum spec, we can't get it uprated except for £xxxx's.


It's power comes off a 50A mcb via a 63A RCD.
Shower is in a bedroom, switch is adjacent, but there is a ceiling fan inside the shower. Cable run about 10m, maybe 12m.


As far as I can remember, the shower is rated at 9kW, so assuming 230V, which we seem to have, give or take, according to my multimeter, just under 40A.


Looking online, 6 sq mm seems to be the norm?


No-one tell me why I can't use a Henley block, double pole, to utilise BOTH 6 sq mm cables already present, before I have to either rave out the existing and run 10 sq mm, or do it via a horrid external conduit...which will probably split in five years like uPVC water pipes do ?

 

 

LOL, wrong bloke: