6mm cable rating

[mike2k06]

Hi all
a friend of mine has just revamped his bathroom due to a flood.
he has ripped out his old shower, dont know what power rating it was.
he is thinking of buying a 8.5kw shower, the cable was already installed, it is 6mm. the length from shower to cu is approx 40 - 45 ft, under plasterboard and floorboards.
what is the max amps for 6mm cable. and would this cable be safe to use for his shower
thank you

 

[dingbat]

Don't you just love these 'a friend has done...' posts?

6sqmm twin and earth cable is rated at 47 Amps at best. At 240V (real, not nominal) your 8.5kW shower will draw 35 Amps. However, the cable rating is affected by the method of installation and could fall by as much as 50% under certain circumstances.

You also have to address the question of how this cable is protected from overload, whether or not the manufacturer recommends RCD protection and whether or not your installation earthing and bonding arrangements are suitable.

So the answer is that the cable may be suitable, maybe not, but without more information it is difficult to say.

 

[mike2k06]

thanks for reply dingbat.
thats what i was trying to explain to him.
but the 6mm cable was already there and now he has already decored his bathroom he doesnt want to rip it out to change cable to 10mm as i reccomended to him.
his cu fuse is the old wire fuse type, but he has an rccb wired in before that.
thanks

 

[dingbat]

...now he has already decored his bathroom he doesnt want to rip it out to change cable...

Same old story. Looks first, safety second.

(And, of course, this cable was tested for insulation resistance and CPC continuity before being reused and its Zs value was verified against the allowable maximum for this unusitable method of protection from overcurrent, wasn't it? )

 

[RF Lighting]

Dont forget the derating factor for BS3036 fuses

 

[Adam_151]

Dont forget the derating factor for BS3036 fuses

But does it apply in this case? unlike the other correction factors that compensate for things which reduce the current caryring capacity of a cable, the BS3036 correction factor compensates for the fusing factor of the fuse and the fact it doesn't give very close overload protection, there is a reg that states you don't need to protect loads that are very unlikely to overload against overload, so if you invoke this reg (and by doing so, you'll have to separately calculate that the cable is adequatly protected against thermal effects of shorts and earth faults) then I'd argue that you can forget that particular correction factor.