"Tim W" wrote in message
...
Sidney Endon-Lee
wibbled on Wednesday 11 November 2009 10:10

I'm looking at replacing a somewhat old consumer unit. I'll freely
admit that my electrical skills are not up to it, and I probably don't
have all the necessary test kit, both of which are a shame.

Anyway, a local firm has scented an opportunity (all the places on the
same development have the same, old, consumer unit) and have sent
round a fuzzy before and after picture of what replacing with a new
RCBO based unit would look like, and estimated a standard price, with
an addition if you need more 'ways'.

Anyway, it looks, from the picture, as though they'd remove isolating
switches and seem to have a design that has:

a) an RCBO per way; and

Which provides the same level of isolation as the MCB that might be there
in
a different, but complaint, installation.

b) an RCBO acting as a 'main fuse', sized to be 'equivalent to' the
current main fuse.

Your "main fuse" is the one in the elect co's cutout, typically near and
definately before the meter.

A time delayed (type S) RCD may be used in place of the main CU isolator,
or
before it in a separate box, if you have a TT (earth rod) installation
earth. This is not and RCBO - it doesn't deal with current overloads and
it
doesn't need to, any more than the main 100A switch in a CU would. The
supplier's fuse does that.

You could also have a non delatey 100A RCD - but this would be essentially
stupid along with RCBOs.

Hence the question in my title. Is an RCBO a suitable isolator?

As much as any equivalent device that might be used is. It will typically
only isolate L and not N (although I have two double pole RCBOs that do
isolate L+N for outside circuits, because it seemed like a good idea,
though beyond basic requirements).

This means that you should not use the RCBO to act as eg as a shower
isolator - you still need the local DP switch. But in every other respect,
the RCBO is a complete replacement for and MCB or fuse.

An RCBO can eliminate equipotential bonding in bathrooms. I believe the
lights and power all have to be off the same RCBO.