In an earlier contribution to this discussion,
Andy Wade wrote:
Hi Andy,
Many thanks for your latest answers.
What would be the effect on the calculations if it were a 40A or 45A
BS1361 fuse rather than 30A?
The first question here is why would you want a 40+ A feed when your
stated load in the garage is only about 20 A? Gut feel says that for
40+ A the submain would need to be in at least 10 mm^2 and that 6 is
likely to be marginal at best.
I think someone else suggested 40A or 45A to provide greater discrimination
between the protection devices - but 30 A is adequate, and I've already got
some fuses, so I'll stick with that.
By now you should see why (in June) I said stick to a 30/32 A circuit.
Indeed!
Incidentally, there's a restriction on wiring in a bathroom that you
need to consider. Wiring which is in Zones 0, 1 or 2 and is not in
metal conduit or is not done in a metal-clad cable such as SWA is only
allowed to supply equipment in those bathroom Zones. This applies
even if the wiring is on the surface or in the normal safe zones -
see Reg. 601-07-01. However it doesn't apply if the cable is buried
50 mm deep in the wall. So if your old shower cable is over the
bath (Zones 1 & 2) you'll have to bury it more than 50 mm in the wall
in order to be able divert it for another purpose. The Zones finish
at 3 m above the floor, so there's a get-out if you have high
ceilings. For the region alongside a bath (where a shower
pull-switch might previously have been located) Zone 2 finishes at
2.25 m above the floor and 601-07-01 then ceases to apply.
It's not a bathroom per se in that it doesn't contain a bath. It's an
en-suite facility which has a toilet and bidet one end, and a wash basin and
shower cubicle the other end. Does that make any difference? The relevant
bit looks like
http://www.mills37.plus.com/en-suite.JPG
The pull switch on the ceiling is for isolating the shower pump. It used to
be fed by the 6mm cable but is now fed by a fused spur off a ring main. You
can see the 6mm cable lying across the small hole I have made in the
ceiling. It would need to be chased into the wall, and then go out through
the wall just to the left of the fan. [It needs to come down to this level
to get below the fascia on the outside]. I don't know what zone that would
be. Please advise! What is the reason for not having any cables which are on
their way elsewhere - sounds a bit OTT?!
Someone suggested using a different type of CU in the garage - so
that if I were to do something with a power tool which caused the
RCD to trip, it wouldn't also take out the lights. Is that what is
meant by a 'split load' CU? Any suggestions as to exactly what I
would need (make, model, etc.)?
Yes, it would be split load. This was covered earlier in the thread
and I made some suggestions then. Again:
Yes, for TT a main switch and two RCBOs would be a good option, or
main switch with one MCB (lights) and one RCBO (power) for TN. I'd be
inclined to make the 'power' RCBO a 20 A one - RCBOs only come as
Type B and 16 A Type B might tend to trip on motor starting currents,
or the inrush current of a 230 - 115 V tool transformer. (Alternatively
keep the 16 A circuit for sockets only and provide
separate motor circuits for any machines.) You can buy all the MK
consumer unit parts separately from a wholesaler, including TLC if
you want to buy on-line.
Thanks. John Rumm has also made some useful suggestions. Many thanks to you
both!
--
Cheers,
Roger
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