DIYbanter - View Single Post - Wiring Ring mains to MCBs in consumer units

(jamie T) wrote in message . com...
In my flat I've discovered that each end of the two socket ring mains
go back to separate MCBs. I've tested this by using a multimeter,
turning off an MCB and still getting 240V on the live terminal (i.e
I've got to switch off 2 MCBs to turn off the circuit). To clarify I
have 2 32A MCBs per ring main, (4 in total). I would have thought
that both ends of the ring main should go back to the same MCB (i.e.
two wires into the MCB) The way it's been wired, each individual live
wire goes back to an individual MCB.

Have I got 2 MCBs too many in my fusebox. I think its wired
incorrectly am I right

Thanks.

Jamie

Well, at the best this setup is non-standard and dangerously confusing
(unless very clearly marked). However I would very much doubt that it
is anything other than either a bad example of DIY or some typical
cowboy work. I am not sure it the regs specifically forbid wiring
multiple paths (they probably don't as it is not really a rational
thing to do anyway) but at the very least you would need the wiring to
be able to safely carry the 64A that you are effectively protected by
(assuming a single load or fault at the mid-point of this "ring"). In
this 32A+32A case you would need 6mm^2 conductors (rather large for a
ring). Anyone got the time to do the calculations for a non mid-placd
max load?

Anyway - whatever the calculations end up giving you for a "safe"
layout (if it ever can be) I can't imagine you ever needing that much
power in a flat. It's not a vast penthouse by any chance is it?

Matt

P.S. Short answer... theres something very wrong with your wiring!!