I'm about to have a hot tub delivered and installed in the garden. ?Before it arrives I have to provide a supply from a 32 Amp breaker through and RCD with a 4 metre SWA tail at the instalation point. ?The run from the consumer point to the location for the hot tub is about 20 metres and, with a 3 kW heater and four pumps, the start-up load of the unit will probably use a fair proportion of the 32Amp rating.

Having done most of my own house wiring and electrical instalation over the last 20 years, the thought of doing the work myself doesn't phase me. ?However, I have never installed an RCD or used SWA cable before. ?I did consider asking an electrician, but gave up because I couldn't get sensible or timely responses.

I currently have a Wylex Consumer Unit which includes a spare 30Amp breaker, but no RCD.  However, it's obsolete, so I can't get an RCD / RCBO to fit it.  I will use the existing 30Amp breaker for the supply.

My proposal is to run 6mm twin and earth from the consumer unit to a point just inside the garage where I will locate the RCD, then I will run 6mm three core SWA from the RCD for the remaining 10 metres to the hot tub. ?My questions are, is the cabling the correct size?, do I need to earth the steel wire covering of the cable as well as use one of the 3 cores as an earth back to the consumer unit earth? ?If so, should the steel wire covering be earthed to a separate earth stake (someone suggested this, but I can't see the need)? ?Do I need a special box for the RCD in order to accommodate the gland of SWA cable? ?Finally, I have a Proteus 32A, 30mA RCBO which has a black fly lead, the instructions aren't very clear - guidance on how this should be wired would be helpful. ?I assume that it goes to a point where it will connect with the neutral Line with the live Line going to the bus bar?

All advice will be gratefully received.

Note: You may be wondering why I have an RCBO.  It's because I didn't know it was different to an RCD until I got home and read the instructions by which time CEF was shut!

Jerry

Thanks.  Coincidently, I used to live in Ash Vale (23 years ago).  I now live in the Midlands - pity you don't, I get you to do the job!

I assume that I wire the SWA steel wire and the core wire (used for earth) to the same earth terminal in the CU.

I can't use the RCBO in the CU as the CU is 19 years old and I can't get parts to fit (it has no RCD).  City Electrical Factors sold me a small CU to fit it in.  I could use this as the junction for the 6mm T&E and the SWA with the RCBO as an extra breaker.  However, as I already have a spare 30Amp breaker in the existing CU, it may be more sensible for me to exchange the RCBO for a simple RCD in its own box.  What do you think?

Jerry

Steel armours earthed to the same point as the yellow core, onto the earth in the 6mm T+E

Thanks chaps.  I know where to come with any future queries.  Never thought I'd get answers this quick.

Jerry

A final thought.  On looking through supplier catalogues on line, I note that there is a shortage of 32Amp 30mA RCDs.  I assume that it's OK to use a 40Amp 30mA version as the overload issue will be covered by the mini breaker in the CU?

Jerry

yup

higher current rated rcds are more expensive to make
however haveing a wider stock range also increases expenses

so the manufactureres set up thier ranges to find the best comprimise between theese issues