wiring in a shower

gull5426

hi everyone,

we have a 9kw shower, which has 4mm cable and is rated at 39 amps.

we are having a new bathroom fitted ( if its costed inside our budget),

the shower has been in for the past 8 or 9 years and have had no problems with it, and as everyone that come and measures up for our bathroom tells us its a really good shower, so now we wont be changing it but we want the pipes sunk into the wall and want it to be inside any new regulations.

the fitters that work for the bathroom showroom company say its fine as they looked into our fuse box only, which is a new type one fitted in the last 2 years. but our gut feeling is we dont like them.

we have now had a separate registered electrican come and look at it (he is the one that fitted the fuse box ) and he says we need the shower re-wiring as it should be 10mm cable.

i welcome anyone elses opinions


thanks

googler

diydoctor says;

Showers up to 7kw may carry a 6mm cable as long as the shower unit is within 18 metres of the fuseboard. Fuses and switches should be rated at 32 amps.

Showers up to 8.5kw may carry a 6mm cable as long as the shower unit is within 18 meters of the fuseboard. Fuses and switches should be rated at 40 amps.

Showers up to 9.5kw carry a 10mm cable to units within 35 metres of the fuseboard. Fuses and switches should be rated at 45amp

Showers up to 12.5kw should carry a 10mm cable to units within 35 metres of the fuseboard. Fuses and switches should be rated at 50 amps.

In all cases the circuit should be interrupted by a double pole pull cord switch with a neon on/off indicator and a mechanical indicator should the neon fail.

It is essential, in all cases, that the shower supply pipes are independently cross bonded to earth.

Which would seem to tie in with the registered sparkie's view....

muckybutt

Twice in one night im gonna say Jesus wept !

4mm cable on a 9.5kw shower ?????? to be frank - im surprised you still have a house left....really. Using a shower of that rating with that cable im surprised it has'nt caused a fire.

10mm cable minimum required, depending also on distance from consumer unit to shower it could even require a 16mm.

Please do not use it again until it has been replaced.

DVardysShadow

muckybutt wrote: »

Twice in one night im gonna say Jesus wept !

4mm cable on a 9.5kw shower ?????? to be frank - im surprised you still have a house left....really. Using a shower of that rating with that cable im surprised it has'nt caused a fire.

10mm cable minimum required, depending also on distance from consumer unit to shower it could even require a 16mm.

Please do not use it again until it has been replaced.

Agree.

OP, look at googler's post above. You will see that cables of any given thickness have a maximum length for a fuse rating.

Firstly the cable has to be thick enough to take the current. But secondly it has to be short enough that any fault at the far end will blow the fuse or the circuit breaker. With a 4mm2 cable, you run the risk of melting the insulation, causing a short - and then not having a high enough current to operate circuit protection, leaving you with an ongoing source of heat in a cable

Poppycat

when we had a new shower fitted from old one last year they had to take a new cable from consumer unit in hallway into kids bedroom above into attic along attic to other side of the house into wall on outside of bathroom and fit a isolated switch also take a copper pipe from attic down wall into shower

bennymac

I assume the regulations must have changed then ? when I fitted one some 15 years ago a 9kw shower was allowed with 6mm twin and earth with a double pole double throw isolation switch.

Jonesya

Cables don't have a single current rating, their rating depends on how they are installed so for example a 4mm twin and earth cable can carry upto 37A if clipped onto the surface of a wall or embedded within masonry. If you run 4mm cable under loft insulation or even just have it passing through insulation it as it drops down from the rafters into the room, the capacity of the cable can drop to 22A or even less.

The only way 4mm twin and earth cable could possibly supply a 9kW shower is if the cable was suspended in free air along it's entire length - this means the cable is either hung from a catenery wire, clipped to a cable tray or held by supports off a wall, which would make for one very unusual bathroom!

It does need rewiring.

Justicia

bennymac wrote: »

I assume the regulations must have changed then ? when I fitted one some 15 years ago a 9kw shower was allowed with 6mm twin and earth with a double pole double throw isolation switch.

Quite a few things have changed in the Wiring Regulations in the last 15 years (new 17th edition issued in 2008), I can assure you

gull5426

thanks for your replies,

will get it re-wired definatly.