"Patrick Olner" wrote in message
om...
I've just run 6mm SWA from the consumer unit in the house to a
workshop some 25m away. The workshop has 4 circuits - 2 lighting and 2
smallish ringmains, run in 2.5mm. The SWA from the house will feed a 4
way CU in the workshop via a separate RCD - my questions a
What size is the armoured cable ? An RCD only gives protection if an earth
fault occurs, so make sure you have a good earth point at the workshop and
don't rely on the armoured cable taking the whole brunt. The MCB you use in
the house is to protect the supply cable to the workshop from melting and
not just to give you enough load for the workshop.
1. What size MCB needs to be fitted to the 6mm SWA in the house CU -
32a or 40a?
Depends on what you intend to use in the workshop.
2. What size MCB needs to be fitted in the workshop's CU - 32a for the
ring and 6a for the lights?
This would be the norm' for a standard installation, but it depends on what
your supply cable can handle in terms of maximum load at that length.
3. How do I avoid the lack of discrimination caused by running 2 MCB's
in line - ideas include i, using type C's in the workshop or ii,
discrimination will be provided by having 40a MCB in the house and 32a
in the workshop or iii fitting traditional fuses in the workshop,
rather than MCB's
Am I on the right wavelength? Any guidance/advice/tips or suggestions
wll be lapped up... thanks everyone for a great NG
cheers, Patrick
If you can, try taking the workshop supply from a separate single way metal
clad consumer unit in the house. This doesn't have to have any RCD if you
have one installed in the workshop with a good earthing point and can be
used with a hard wired fuse to reduce any erroneous tripping. It gives more
protection from faults in the workshop back to the house.
Get some 16 mm Double Insulted Cable and Two Terminal Blocks from your
wholesaler. Take the fuse out from the mains supply unit (the bit before
the meter) and then disconnect the supply cables from the meter at the mains
switch of the existing consumer unit and put them in the big terminal
blocks. Cut the double insulated to the lengths you need to go to both the
existing fuse box and your new single way unit. Connect them all up to the
terminal blocks and you then have two separate supplies, one for the house
and one for the workshop, but all running through the same meter. Believe
me, it stops any conflicts.
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