(Andrew Gabriel) wrote in message ...
In article ,
(Patrick Olner) writes:
- thanks very much to one and all - yet again this fantastic resource
and the absolute stars within it have saved the day!

- Andrew, no problem with machines and lighting etc - the workshop
will be half darkroom and half craft area, so it does need to supply
some pretty hefty items - print processor, water heater, etc, as well
as the more usual run o'the mill stuff.

OK, this might be more than I imagined. Can you estimate the power
(or better, the VA rating if you know) of all the devices, and
estimate the total maximum you might operate at once. For the
water heater, please state its type, and in the case of a stored
water heater, its water capacity.

With regard to workshop having it's own earth rod - is this strongly
advised?

It's theoretically safer, but I don't know if many professional
electricians would bother. If the workshop building includes metal
structural members which can be touched from outside, I personally
would certainly do this (metal greenhouse is a good example of such).
What type of earthing system is your house supply? (See
http://www.diyfaq.org.uk/electrical.html#system for descriptions.)

I also should have mentioned that that the fuse supplying the
workshop is on the RCD side of a split way consumer unit ... so do I
really need RCD protection with the workshop too?

No.
However, it's not a good idea to share indoor and external circuits
on the same RCD as it's too easy to trip them (mallicious or water
ingress) and lose power in the house. It is however not against the
regs to do this. You should have a double pole isolating switch for
the external circuit -- a dedicated RCD operating on both poles can
double up to perform this function.

Should I decide to
do so .. would the 40a cartridge fuse in the house consumer unit be OK
being fitted on the RCD side of the house CU?

I should also have asked what the value of your main fuse is. If it's
only 60A for example, that's not enough to provide safe discrimination
against a 40A fuse. If it's 100A, then that's OK. Also, you need to
do a load calculation to ensure you aren't going to be overloading
your house supply.

Andrew .. thank you so much for your guidance it truly is invaluable
... - yes we only have 60A main fuse, how much of a problem do you
think this will and how the hell would I go about changing it? - the
main items that will run at once are
1. Water heater, not sure of it's type - a white box about
16"x16"x12", 2kw, it has a 10 written on a small silver label with
it's voltage, wattage, etc which may or may not be 10 litres, sorry to
be so vague;
2. Print processor, 2.7kw;
3. Ventilation, 70W
4. Enlarger, 250w
5. Film dryer, 500w
6. Depending on the South Wales winter - possibly a heater too, 2-3kw
6. Maybe one or two electric tools such as circular saw, sander,
planer etc
7. Outside lighting, 3x150w halogen PIR security lights
oh .. and the obligatory kettle!

Also Andrew, how do I do a load calculation?
You are the almighty and I am truly humbled - best wishes, Patrick