RCD?

Does anyone know if it is sufficient to install an electric shower in a property with an old fuse box consumer unit, and protect it with only a plug-in mcb, rather than employing the ideal solution of installing a separate shower consumer unit. I am pretty sure it is dependant on the fault current whether an RCD needs to be used.

if it is an electric shower you can not "plug it in" there for you can not use a "plug in " rcd

if its a power shower then yes that will be fine

Thank you for the swift reply. As a plug in mcb I meant the type that plugs into a spare fuse way in the old type boxes. This obviously will not provide the same switch off time as an RCD should a fault develop and works on the principle of overcurrent rather than a earth fault current, so do the regulations allow the use of an mcb alone?

Yes you can use a plug in MCB.

You could put an RCD in an enclosure between the fuseboard and the shower switch(din rail enclosure). Probably best adjacent to the fuseboard.

RCD's are not required on showers by the regs under normal circumstances, but most (if not all) sparks will install one.

Thanks for the advice mate, much appreciated. The shower that is to be installed is 9.5KW which works out to be nearly 41.5A at full load. The resident has an old type fuse box with a 60A isolator. The electricity board fuse has displayed on it '60/80A'?? Other web sites say that a 9.5KW shower can't be run with this size fuse and isolator in-line. What is your opinion. Thanks for your time mate.

the service fuse is a bit low but many recs take a "we won't change it until you blow it" attitude and to be honest those service fuses take a *LONG* time to blow at small overloads

wylex standard consumer units with a main isolator below 100A are not supposed to take protective devices over 32A though they CAN be forced in this is not reccomended

so you will either have to henly in a shower CU or replace the main CU

both of theese involve removal of the service fuse
in theory you are supposed to get the rec to do this but they are often unresponsive on the issue

many electricans just pull the fuse themselves and the recs don't seem bothered about this practice

It is not something we would generally advise diyers to do but if you do pull it make sure the main switches of all consumer units fed from it are OFF when pulling and reinserting it and make sure you don't touch any metal parts of the fuse unit.

Finally i have heared there are some unual designs of service fuse units around so make sure you PROVE DEAD with a meter before you start changing any wiring

Personally, I would not consider a shower without an RCD, and certainly not fitting a breaker greater than 32A to a Wylex board with a sub-100A main switch.

Kill two birds with one stone and fit a sep. 1 or 2 way CU with an RCD incomer and feed the shower from that.

Thanks again for the advice people, it is very much appreciated.
If I decide to go along the route of fitting a separate shower CU will I need to uprate the meter tails as I will be feeding another load which is 2/3 the size again of the origional CU? I am not entirely sure of the size of the tails already there, but this is a really old install.