Have I understood correctly ?

[Turpin]

Darned confusing this cable size lark...

I was checking my new shower circuit for a 9.5kw shower - just received certs for it (thanks to all here for info) and it appears to be a 13mm w x 7mm h on the pvc sleething - tape measure job of the measurement.

So, by my reckoning (and use of http://www.wiki.diyfaq.org.uk/index.php?title=Cables ) this would suggest that this is 6mm2 cable.

Now that sounds like it aint enough for a 9.5kw shower on a 45A fuse. But I looked a bit deeper and saw that it depends on it's installation method - notated from A - E, as this is a new cable run, solely for the shower, up a cavity in a non-insulated wall, above the lagging and joists in the loft and down a stud wall (again a cavity), this is ok as it's a 'C' type installation that is rated to 47A ? It's a T&E cable.

Cert with the test info on this seems to back this up, and the cable is definitely stranded.

Would it be better to swap it out for 10mm just in case ? I wouldn't want my new shower tripping.

 

[securespark]

Length of circuit?

Standard circuit arrangements suggest 10mm² for a 9.5kW.

 

[Turpin]

Length of circuit?

Standard circuit arrangements suggest 10mm² for a 9.5kW.

It's approx 6m long, CU is in garage, directly above is the bathroom on 1st floor, run is via loft - all of 1m of the run is in the loft. Wall down to shower is a false wall.

The cable is seperate from any others - apart from where it enters the CU.

 

[Steve]

Would it be better to swap it out for 10mm just in case ? I wouldn't want my new shower tripping.

Undersized cable wont cause an MCB to trip. Thats the problem It'll just overheat.

 

[pompeygit]

Most would use 10mm² as a matter of course on a 9.5kw shower as it offers a safe margin and saves doing calcs. In your case the circuit is ok and should not trip the breaker as you are running 6mm² for only 6metres presumably on a type b breaker. The voltage drop is only 1.8 volts and the circuit fufills all the requirements:
In greater than or equal to Ib
In less than or equal to Iz
I2 less than or equal to Iz
Without knowing the ze there is no way of knowing if the circuit satifies shock risk or thermal constaints, but I would not imagine for a moment there is a problem with these if you have a typical supply.

 

[Turpin]

Would it be better to swap it out for 10mm just in case ? I wouldn't want my new shower tripping.

Undersized cable wont cause an MCB to trip. Thats the problem It'll just overheat.

D'oh, of course!

Thanks all for the info, is there anything simple I can do to make sure it's all ok? Have a shower and check the temp of the cable? Would it be warm / hot under normal circumstances or only if it's on its way to overheating ?

Sorry if that sounds daft !

 

[pompeygit]

cables insulation is designed for the fact that cables get warm. Your cable should reach 70c safely at 47amps, but I doubt for a minute it will get that hot as it will be taking between 39-41amps. You will smell it if there is anything 'fishy' going on

 

[Turpin]

cables insulation is designed for the fact that cables get warm. Your cable should reach 70c safely at 47amps, but I doubt for a minute it will get that hot as it will be taking between 39-41amps. You will smell it if there is anything 'fishy' going on

Cheers for the info, first couple of uses I'll probably have a sniff and a feel... so to speak.

 

[sparkydude]

If you have recieved a test certificate then it should state the cable size and its related protectived device . There should be no need to guess the size of the cable

Nick