The way my installation has been done (not all by me!) is....
Live and Neutral enter my CU from my meter directly into a 80A RCD (MK model
No LN 5780)
There is an earth wire coming out of the bottom of the electricity companies
fuse box that runs to the CU (via a sealed (metal loops of wire with a lead
like lump on) little box
I am in the process of trying to get the electricity board to come out and
disconnect my main fuse so I can install a 100A isolator in between the
meter and the CU, as I am intending wiring in a generator transfer switch
(it's on the wall already!))
Off the 80A RCD are the following MCB's (nearest to furthest)
30A 30A 30A 20A 15A 10A
There is then some wire connected to the same terminals as the incoming
supply (looks like 2.5mm) that then goes to the input of the lighting RCD
(MK number 6730), this then has three 5A MCB's connected to it that supply
all the lighting in the house.
(This is all in a single consumer unit)
My first question is, is this correct - I am concerned that the wires that
run from the top (inlet) of the first RCD to the inlet of the second
(lighting) RCD are not sufficiently protected (the only thing protecting
them is the 80A electricity board fuse)
My next set of question start with....
There is a 15A MCB for the outside power - There is a 2.5mm T&E cable that
runs from the CU to the workshop
It used to run to an old shed, but we have got a new one due to the fact it
practically fell down! This old shed was supplied form the house via an
overhead 2.5mm cable attached to a galvanised wire (this bit was about 5
The new workshop is slightly closer, so I have just moved the cable over to
the new location - This overhead run is now about 4 Meters from the house to
In the old shed there was a crappy old fuse box - This has gone in the skip
as it was rusty, and sometimes tripped the main RCD when it was switched
I have installed a new consumer unit in the new workshop
This has a 30mA RCD
The sockets in the workshop are connected to a 15A MCB
The lights in the workshop are connected to a 5A MCB
There is another shed right next to the workshop, this too has it's own 15A
MCB for the sockets, and a 5A for the lights
The cables to the other shed are run through a length of green corrugated
plastic pipe, remarkably similar to what NTL use from the tee in the road to
the drop box ;) - As I said before, the shed is right next to the workshop,
so the pipe is only about 15cms long!
There is then a 2.5mm T&E cable that runs from a 15A MCB in the workshop,
through the other shed, then underground (in what looks like water pipe) to
the garage at the top of the garden (about 25M away)
This currently has yet another CU with two fuses, one 15A for the sockets,
and a 5A for the lights.
Then from this garage, wired into the 15A fuse (along with a socket in the
garage), there is a 1.5mm T&E cable that runs to the greenhouse (to one
water proof switched un-fused socket)
It may seem a lot running off the one 15A MCB in the house, but it has never
tripped as there is not a lot of power used outside (Two pond pumps, a few
lights, and the occasional use of hedge trimmers, strimmers, power tools and
Does this all look OK or not?
Everything is electrically protected as far as I can see (There are no
cables rated under the rating of its supplying RCD or MCB)
The things I am concerned about are...
It is all earthed from the house - should I install an earth rod at the
workshop, garage or both? (I have installed an earth rod for the generator
witch is located next to the workshop - could I use this one rod for two
The overhead cable is just bog standard T&E - I expect this should be either
in a pipe of some sort, or armoured?
The cable that runs up to the garage is also bog standard T&E - it is
protected by the water pipe it is in, but should it be armoured really?
Should I replace the old fuse box in the garage with yet another RCD/MCB
People say you should not have RCD's connected to RCD's - why? - Surely is
it just more protection?
Thanks for you comments!