Shower Cable...

[SSE]

Was speaking to someone today who said they were upgrading there shower to a 8.5kw but not changing the cable which is a 6mm. He said it's a run of about ten meteres going through floorboards and up to switch. Surely this must be borderline? personally I would use a 10mm2 but just thought I would see what you guys thought.

 

[AndrewMgan1976]

If it is clipped direct 6mm can take 47 amp, so no problem with the cable

 

[sparky1502]

well anythin over 8.5 will need to be run in 10mm2 as you said, i would run it in the 10mm2 to cover my own end....

 

[ezzzekiel]

depends on the method of installation, although its common practice to install 10mm its not always necc

 

[Sintra]

I think that only acceptible method of installation for a 6mm cable would be clipped direct protected by a 40 MCB.
Any other installation method would not give you a 40A rating needed for the overcurrent protective device.

 

[super_stuey]

Best way 2 cover yourself is by using calculations to prove it! Thats why we get taught the damn things.

As previously stated 6mm can take 47 amps clipped direct and with the price of copper rocketing I cant see why anybody would waste time and money running 10mm when not necessary.

Use the force brothers, use the maths!!

 

[JamesBrownLive]

I think that only acceptible method of installation for a 6mm cable would be clipped direct protected by a 40 MCB.

Aren't all circuits that supply bathrooms now required to be RCD protected ?

 

[Sintra]

Aren't all circuits that supply bathrooms now required to be RCD protected ?

Absolutley should have mentioned backed up by 30mA rcd but my post was mainly aimed at the cable size required and the overcurrent rating of the protective device.

 

[telepath]

How many of you have seen a shower cable clipped direct?

The existing cable is bound to be buried in the wall and since the shower will draw a current of 37 Amps a cable upgrade is surely necessary, unless you hack the cable out to clip direct.

 

[rocker]

6mm will carry 47A under reference method C, which is both clipped direct AND/OR embedded in plaster. It will carry 41 under method B which is conduit or trunking either on surface or embedded.

An 8.5kW shower pulls 36.9A at nominal voltage. Round 'ere, voltage is usually closer to 240 which, in the real world, brings this figure down even further. The only place we are really going to have problems with this is when the cable is run through thermal insulation (meth A), which gives us only 34A, and decreases with similar methods (100, 101, 102, 103 etc).

For the record, if they are upgrading to an 8.5 on 6mm, and I can't see presence of insulation in the run, I will put the shower on this cable with a 40A breaker (and RCD of course), but if I was installing the shower from scratch, then I woud put in a 10mm.

This is my interpretaion, anyway, please let me know if I am wrong.

 

[JamesBrownLive]

6mm will carry 47A under reference method C, which is both clipped direct AND/OR embedded in plaster. It will carry 41 under method B which is conduit or trunking either on surface or embedded.

I'm certainly not questioning your knowledge Rocker, more prehaps the Regs, how can something embedded in plaster, carry more current than something in conduit. Surely a cable completely surrounded by plaster will cool down much slower than a cable in conduit with some air around it

Or am I missing the point entirely

Cheers

 

[rocker]

I often think of this myself, but I guess if you think of your hand in a cool room, if you stick your hand out in front of you you may feel a draught, but not a great deal. If you then go and touch a wall, it will feel cold. The plaster is a better conductor of heat than the air, so it draws heat out of your hand more efficiently than the air does. If you then put a glove made from fiberglass insulation on your hand, apart from becoming itchy, your hand woud warm up, as it is nsulating your hand from both the air and the wall, and not allowing it to transfer any heat. Because your hand is generating heat, but the heat is not disspiating into a conductive surface, your hand hets hotter. It's the same with cable, I think so anyway.

 

[drywax]

I often think of this myself, but I guess if you think of your hand in a cool room, if you stick your hand out in front of you you may feel a draught, but not a great deal. If you then go and touch a wall, it will feel cold. The plaster is a better conductor of heat than the air, so it draws heat out of your hand more efficiently than the air does. If you then put a glove made from fiberglass insulation on your hand, apart from becoming itchy, your hand woud warm up, as it is nsulating your hand from both the air and the wall, and not allowing it to transfer any heat. Because your hand is generating heat, but the heat is not disspiating into a conductive surface, your hand hets hotter. It's the same with cable, I think so anyway.

Now that answer is what we all wanted if only everything else was explained so simply

 

[JamesBrownLive]

I often think of this myself, but I guess if you think of your hand in a cool room, if you stick your hand out in front of you you may feel a draught, but not a great deal. If you then go and touch a wall, it will feel cold. The plaster is a better conductor of heat than the air, so it draws heat out of your hand more efficiently than the air does. If you then put a glove made from fiberglass insulation on your hand, apart from becoming itchy, your hand woud warm up, as it is nsulating your hand from both the air and the wall, and not allowing it to transfer any heat. Because your hand is generating heat, but the heat is not disspiating into a conductive surface, your hand hets hotter. It's the same with cable, I think so anyway.

That certainly makes sense, I guess I just always thought of plaster as an insulator, rather than a conductor. I'm sure those boffins at the IEE, or should I say IET, know what they're talking about

Cheers

 

[telepath]

6mm will carry 47A under reference method C, which is both clipped direct AND/OR embedded in plaster. It will carry 41 under method B which is conduit or trunking either on surface or embedded.

An 8.5kW shower pulls 36.9A at nominal voltage. Round 'ere, voltage is usually closer to 240 which, in the real world, brings this figure down even further. The only place we are really going to have problems with this is when the cable is run through thermal insulation (meth A), which gives us only 34A, and decreases with similar methods (100, 101, 102, 103 etc).

For the record, if they are upgrading to an 8.5 on 6mm, and I can't see presence of insulation in the run, I will put the shower on this cable with a 40A breaker (and RCD of course), but if I was installing the shower from scratch, then I woud put in a 10mm.

This is my interpretaion, anyway, please let me know if I am wrong.

Are you using the correct table for your current carrying capacity. It seems to be from table 4D1A, which is for single core cable.
Not that it would have any effect on this circuit, but table 4D2A gives reference method C as 46A, method B as 38A and method A as 32A.


Thanks for the information as regards to reference method C, which is both clipped direct AND/OR embedded in plaster. I always thought that this meant clipped direct only.