Connecting a shower - RCD confusion - PLEASE HELP!

[niccon]

Dear all,

I soon intend to install a 9.5kW electric shower to the home of a close friend whose bathroom I will be renovating. I have had previous experience with home electrics and have also worked with a qualified electrician rewiring a house once before, so I am not completely new to the subject. I have read the IEE installation method described on some DIY web sites and understand fairly well the proceedure for making such an installation. However, I am confused over one particular point of the installation.

Whilst I understand the need for the use of an RCD unit in the connection of this device to the mains, I am not quite certain on how to use the unit.

My friends CU is a fairly modern Wylex unit. It has a maximum rating of 100A on the main switch and is split into 2 sections, 1 with the mains ring and immersion heater on an RCD and the other with the remaining circuits such as the lights, cooker, etc.

There are 3 empty fuse blocks (spares) on the side of the RCD. Whilst I understand that the shower unit must have its own 45A RCD, I am not sure whether to fit this on 2 of the 3 spare slots (shifting lower ampages across accordingly), or wether I should upgrade the existing RCD on the CU and add the shower to this through a 45A MCB or whether I should install a RCD unit seperate to the CU and have the electricity company link it to the meter.

The other thing on my mind is that I will be installing a bath with a spa system and am not sure if this too will require a separate RCD or if it can be placed on the rail of the existing RCD in the CU.

Please help if you have the answer. Thank You.

niccon

P.S. I intend to get the final installation checked by a certified electrician before turning on the power, but I still want to get it done right so as to avoid timewasting.

 

[comms]

Sounds like the cu is a split load board type, so the shower circuit goes to the rcd protected side (no need to fit a seperate rcd) just fit a mcb to the correct rating for the shower.

 

[securespark]

.....making sure that the existing s/l RCD is rated at at least 80A...

Also, the main isolator should be rated at 100A (OK in your case) and it may be as well to get the REC to upgrade the supply fuse and/or meter, if these are below 100A.

9,5 kW @ 230V is just over 41A, so you can appreciate this is a fair chunk of the total available.

Add a couple of rings, an immersion, electric cooker etc, and you can see that it will not take much to be nudging the ton.

 

[Adam_151]

Might be better to use an RCBO on the non RCD side:

1) you don't have to worry that the extra load will push the RCD over the limit
2) if the RCD nuisence trips, you arn't going to end up wet, half washed, sans clothes going across the house to reset it... ,a RCBO will be dedicated to the shower so won't have the earth leakage to computers etc that could trip it, also it won't be affected by dodgy toasters plugged into the ring (damn you £6 toaster from asda...)