PoP wrote:
On Wed, 03 Dec 2003 14:56:26 +0000, Andy Hall
wrote:

And for that matter, has anyone got any tales, good or bad, about the
Screwfix Garage Consumer Unit? Its a 40A RCD unit with two (6A and
16A) MCBs.

Is that enough or are you sure it will be enough for future
requirements.

I've got a similar model in my garage (not identical) with 2 RCD
protected circuits - 6A and 16A.

I just got thru wiring an electric fan heater in there today. Being a
3KW jobbie it's going to pull some 12A when operational. That leaves
4A or about 1KW before the RCD pops its clogs, which will compromise
some of my power tools!

Haven't thought about this problem before (I have to admit I assumed
it would be a 30A supply). I'm wondering whether a solution is as
simple as uprating the RCD, or am I going to have to consider other
alternatives?

You've got your RCDs and MCBs confused, I think.

The 6 amp and 16 amp rated things in your garage CU are MCBs, that is
they're overcurrent devices. Hopefully there is *also* an RCD
protecting at least the 16 amp sockets circuit. The usual arrangement
is that the incomer switch device on the mini CU is an RCD (rated at
30mA trip current) which feeds the two MCBs. (A less likely
possibility is that you have RCBOs, combined RCD/MCB devices)

One fairly simple approach would be to uprate the 16A MCB to a 20A
one, this would be 'correct' for a radial circuit wired in 2.5sq mm
feeding sockets. This would give 8 amps or so 'headroom' for your
machinery. As long as the feed from the house is also at least 2.5sq
mm and isn't too long then this strikes me as the obvious solution.

Garage is fed from an armoured cable from the house - I'll have to
check this further to make sure of capacity but it looks to me to be
beefy enough to handle a higher load. I know the armoured cable comes
thru the house consumer unit 100A RCD because (with the circuit RCD
switched off) the 100A RCD tripped the house out when I chopped thru
the mains cable in the garage - presumably due to some small current
flowing between live and earth even with the circuit off.

It would be touching neutral to earth that tripped the house RCD.

--
Chris Green )