Electric shower/ Cable thickness

[Hake]

Hi All,

Due to my old elc shower spurting water out inside the housing, I have decided to replace it with a nice new one.

My plan was;

Old shower out, fit new shower, get sparky in to make sure the wiring is to spec & safe.

Sounded nice and simple, but on further investigation, its not that easy :-(

Firstly, our old shower was 7KW, the new one will be 8.5KW - this led me to check the wire & MCB was adequate. Having looked, the MCB is a 40A Btype & the wire is bigger than 2.5mm(2) - how can I tell whether it is

4/6/10mm(2)?? It has, I think 6 strands of copper in the individual L & N.

I have looked at the requirements of thicknesses of wire for showers (in the destruction manual for the new shower I am hoping to purchase) It seems that

6mm(2) would be adequate so long as the cable is clipped on to the wall. In this situation, it goes underfloor for about 1m from the CU & is then clipped to the wall unill it reaches the shower.......If the wire is indeed 6mm, is the 40A MCB allready fited OK - as I undersand it, a 8.5kw shower will be fine on a 40A MCB.

Thanks in advance,

Colin

[noelogara]

Yes Colin a 40 amp MCB is correct spec and 6 square cable. you also need a pull cord isolator switch on the cable preferably just outside the bathroom.

2.5amp cable is no use for this job.

[John Rumm]

Usually the case ;-)

You can usually tell by measuring the outside dimentions of the cable:

Cable CSAs Vs Physical Dimensions:

CSA (CPC) Strands Overall mm^2 No./dia. mm approx.

--------- ------- ----------

1.0 (1.0) 1/1.13 4.5 x 8.2 1.5 (1.0) 1/1.38 4.7 x 8.2 2.5 (1.5) 1/1.78* 5.3 x 9.9 4.0 (1.5) 7/0.85 6.1 x 11.4 6.0 (2.5) 7/1.04 6.8 x 13.1 10 (4.0) 7/1.35 8.4 x 16.8 16 (6.0) 7/1.71 9.6 x 19.5

• or 7/0.67

so 13mm across the long axis would be 6mm^2

In many cases this will be true. It will depend on the total length of the cable run, how it is installed and routed, and also on the type of protective device(s) upstream of it.

Yup, 40A MCB should usually be fine.

[Hake]

Thanks John, that list of cable sizes will be usefull, though I have rather bad feling it may be 4mm^2 rather than 6mm^2 mutter, mutter bugger it mutter.

Colin

[John Rumm]

4mm is easy to spot as the CPC (i.e. earth) wire is the same size as that used in 2.5mm^2 cable... (one of the reasons that 4mm^2 is frequently not a particularly useful size).

[Hake]

In that case, I am certain it is 4mm - Time to lift some floor boards :-(.

Thank you again for your help,

Colin