New Shower advice - any electricians on board?

[Gazjam]

Word!

Chaps, getting a 9.5kw shower fitted next week, and the installer says for a 9.5kw shower you "could get away with" 6mm cable to the main electrical board.

Now, I'm not so sure, and to be honest, I'm starting to wonder if the guy knows himself.

Local tradesman, probably fitted loads of the things, sounds like he knows his stuff over the phone, but when I asked if he will be using 10mm twin and earth cable for the installation, he says "Naa, 6mm is fine."

Now, I checked about online and couldn't get a definate answer but general opinion is use 10mm stuff - its rated to carry highter ampage etc etc.

Anyone point to BS Standards or building Regs on this stuff?
Any sparks in the room to advise?

The guy sounded spot on until he mentioned the 6mm cable being fine.
**********************************************
Its a small bathroom, think slightly longer than a standard bath.

The water tank is on one side of the wall, the electrical mains the other side.

No more than about, say, 10-12 meters including the run up both walls and any trunking etc?

Cables will be fed under the bath,

[Covenant]

I didnt uprate my cable when I had a 9.5 KW shower installed a few years ago.
A word of warning-they eat electricity. My 15 year old daughter can spend 20 minutes in the shower and many the time I have been tempted to flick the circuit breaker in the garage to get her out.
I wish I had put a thermostatic in (We have one in the main bathroom). This gives a more satisfying shower as you have twice the volume of water.

[Gazjam]

Cheers Jerry,

was it a lower rated shower you had before?

[Ali Tait]

Hi Gaz,

To work out the size of cable required,you need to work out the current (amperage) that the cable needs to carry.We can use the simple formula-

P=IV

Which means Power-P (Watts) equals I (amps) times V (Volts).

Swapping the formula around to find the current needed,we use this-

I(current)=P(watts) divided by V(Volts).

So,we know the volts already-i.e. UK mains voltage-240 volts.

We also know the power used by the shower-9.5kW,which equals 9500 watts.

So,to find the current the cable needs to comfortably supply-

I (amps) = 9500 divided by 240.

=39.6 amps.

Make it 40 amps to be safe.

6.0 mm p.v.c. cable will carry 41 amps in conduit behind the wall,as long as it's not encased in thermal insulation ( this will reduce the current carrying capacity)

10.0 mm will carry 57 amps in the same situation.


Personally,if it was me,I'd go for 10 mil.

Hope this helps.

[Gazjam]

Sure does Ali, cheers.

I just wonder if the guys only got 6mm in his van and is reluctant to buy some more!

I wondered if it broke any building Regs using 6mm for a 9.5kW Unit.

Also, the cable capacity is a function of distance as well I think?
I read somewhere you could use 6mm if the cable run is less than 20m.

Again, not hard and fast facts online, so looking for first hand experience. :)

[Mike]

While you're at it, you may need an upgrade to your main fuse depending on the age of your house. Some, like mine, only have a 60A fuse. Get a 100A main fuse installed and get a free HiFi upgrade thrown in! :eyebrows:

'Others' have done this and reported good results. :)

[Gazjam]

Is the fuse directional? ;)

[Gazjam]

Another thought, the guy said he will fot a 40A RCD, anywhere Ive read says for a shower rated at 9.5kw its a 45A RCD with 10mm T+E.

Don't want to be an arse and tell the guy his business, but at the same time I dont want anything going BANG and turning black in the shower....

[Ali Tait]

Gaz,
I can answer questions like that in theory no problem,but I will always add that I'm not an electrician,but an electrical fitter,so I don't have 17th edition regs etc.so can't advise as to correct type of cable and lengths etc. and how the regs deal with domestic installs.I deal in high-voltage substations and the like.Frankly,I think the 6mm will be ok in reality in a fairly short run,but I just have a supersafety slant on things,having buried seven work collegues in the last twenty years due to accidents at work.Remember though,the quoted current capacity of a certain size of cable will,like anything else,have a comfortable safety margin,so in reality in a normal house 6.0 mil will be fine.

Note this is just my opinion,seek the advice of a proper domestic spark!!!

P.s. Mike is quite right about upgrading your main breaker,or you may find the new shower will trip your supply.

[Covenant]

Cheers Jerry,

was it a lower rated shower you had before?

Yep-7.5Kw before.

[Gazjam]

Thanks Jerry.
Good information to know.

[Gazjam]

Note this is just my opinion,seek the advice of a proper domestic spark!!!
Noted - but thanks for the advice, its helpful.

P.s. Mike is quite right about upgrading your main breaker,or you may find the new shower will trip your supply.
I think the guy is fitting a seperate 40Amp RCD. This is another concern (potentially) as I think Ive read it should be 45A.

Depends on the draw of the shower at full tilt I guess, but playing it close to the limits not great when using water and electricity.

:) :scratch: Classic scenario of a little knowledge being a dangerous thing! :doh:

[Ali Tait]

Well yes,but obviously just uprate things to allow for a healthy safety margin.These days,given the fact that these kinds of things have a healthy margin thrown in anyway in the quoted specs,if you add your own margin,you'll be extra safe,and that's how I like to be! I've been to too many funereals....

[Gazjam]

Well yes,but obviously just uprate things to allow for a healthy safety margin.These days,given the fact that these kinds of things have a healthy margin thrown in anyway in the quoted specs,if you add your own margin,you'll be extra safe,and that's how I like to be! I've been to too many funereals....

I hear you mate.

Not a big ask to stipulate 10mm cable.
Hell I'll nip down to B&Q if its THAT much of a problem! :)

[Ali Tait]

Well yes,I do admit I may bang on a bit about such things,but I like to err on the side of safety.It's far too easy to take electrickery for granted.As I said,been to too many funerals.

[Gazjam]

My Brother in Law is similar, he's in 3 Para. :(

Tours in Ireland, Bosnia, now over in Helmut for 6 Months.

Poor Sod.
He lost a few mates too..

BUT ON A LIGHTER NOTE........ :)

[Gazjam]

Gawd where did THAT come from?

(Checks Wine bottle......Yup!) :)

Thanks for the shower-related advice Guys.

[alb]

I was told that around 16' of 6mm TE from fusebox to shower was the limit for 9kW. Quoted from my electrical wholesalers. I don't know if this is correct.

Mine was over 20' so i didn't risk it and bought another 8kw shower.

[Ali Tait]

Al,yep by the book excellent info.Most homes would not exceed that by too much,or at least enough to make a difference.I'd still have 10 mil,but that's just me.:)

[DSJR]

When we had our utility/shower room done around four years ago, we had a separate trip switch put in the main fuseboard cupboard (Protek RC80 30/40B, if that means anything to you guys), we also had a high current isolating swich in the room itself (hidden in the utility cupboard) and I think 15A cables were used - we had a Mira 10.5KW/h shower installed in a small cubicle and this gives plenty of HOT water with a decent usable medium setting with our water supply (the low setting barely gets tepid). Works fine when we're in a big hurry to get out and we can have an upstairs unassisted traditional drenching in the bathroom fed from the hot tank and a "quickie" blast downstairs ;)

[JackGold]

Yep-7.5Kw before.

Hello! I had the same shower a couple of years ago...Now I use Stanza Black 9,5 kw.But I dream about a mixer shower (http://www.gainsboroughshowers.co.uk/shower-store/Mixer-Shower/combi-mixer-showers) (GS400 Concealed for example). Mixer showers are more reliable I think. Thanks.

[Mr Pig]

Personally,if it was me,I'd go for 10 mil.

I agree. I don't like running things close to the limit as unforeseen things can happen in the future. We have an electric shower and the current they can draw is phenomenal. For a few years I was forever fixing it as it kept eating microswitches. I replaced loads of them. Turned out the problem was that the spade connectors that attached to the switches were crimped on to the cables and the crimped join had oxidised enough to put the resistance up. The heat generated was baking the switches! I soldered all the joins and not had a switch fail since.

You're better off with something that'll comfortably do the job than just do the job. Tradesmen, generally speaking, are lazy b*******! The probable reason he doesn't want to use 10mm is because it's a pig to bend. 6mm is much easier to work with so if he can get away with it that's what he'll use. Do you think he gives a s*** what happens to your shower ten years from now?

[Rare Bird]

You can't beat the bath mixer tap with shower fitting :)

[Bazil]

FWIW,
I've got a 10.5 kw shower and a long run of 10mm.
Ok to date

[goraman]

6mm solid core will take 600v with teflon,but if it where me I'd go for 10mm solid core as it's the amps that thing could draw.


I'm thankful we have a 200 gallon gas hot water heater to draw from.