DIYbanter - View Single Post - Help! RCD trips on Volex consumer unit no matter what I do!

wrote:
Thanks for the information. I had a feeling I was right about the RCD
being faulty. I'm going to split the circuits for now then and run
the
upstairs and downstairs sockets on a new RCD and run the kitchen
(boiler, fridge, freezer; I don't have an electric cooker or an
immersion heater) and lights without.

ok, just one thing, you need to ensure that a socket likely to be used
by outdoor equipemnt is on an RCD to pass inspection.

I don't have any spare cash at
the moment as I'm doing up a house that time forgot.

OK. If you want you can do it in a way that costs you nothing extra
now, but leaves room to upgrade the RCD aspect later if you ever need
to. The way to do this is just to have a fewe spare ways on the CU so
that MCBs can be replaced with the double wide RCBOs later. You may
never need to do this upgrade, but a significant number of single RCD
protected installs do have ongoing problems.

If youve got time, running a separate wire in for fridge etc would also
enable you to put that on a separate non RCD conection as well. if not
thermally insulated, a 2.5mm radial needs 20A breaker, or 4mm can be
one a 32A breaker.

Just in case theres any unclarity, radial means one wire rather than a
ring.

If youre replastering over the wire runs, now is a good time to put
some low v cable in as well. Cat5e is ideal, but even 4p/metre bell
wire can be quite useful later, for phones, internet, etc. If OTOH
youre running wiring thru floor cavities, including string makes it
possible to pull more wiring through any time later.

Before I put the
new wiring in, I had one spur circuit for lights and one spur circuit
for sockets.

I guess you mean radials, with each item spurred off the previous. Even
round pin sockets shouldnt be wired like that.

There was one surface mouted socket in each room, and a
few round pin type bakelite sockets too, to go with the bakelite
light
switches.

ohhh.

Nasty. Once it's all in I'm going to get it certified.
On top of this, there wasn't any earth at all until I put one in. The
mains supply is labelled as being PME but there was no connection for
earth.

The neutral feed will be the PME earth. PME is a method of using the
neutral as earth as well.

At the moment I've earthed the CU via the cold water inlet,
which is cast iron and the gas inlet (which I have just had replaced)
which is now copper.

ok, that should work ok, but will not pass inspection. You need a pukka
earth rod with inspection pit, and earthy things need to be connected
up with the right size wire.

Bathroom equipotential bonding is also required for a pass.

Presumably then, my system is acting as a TT
system?

yep. Running it as PME would be better really, and cheaper as theres
then no need for a whole house 100mA time delayed RCD.

The regs say a 30mA RCD though and don't mention a time delay
for a TT system.....?

it is required regs wise - and it matters, as TT earths are often
inadequate to blow the MCBs. With a TT earth and less than complete RCd
cover, you could have a fault running to earth and the entire earthed
system sit there live, waiting to bite everyone, and gobbling power.

Thanks for the advice. Much appreciated.

Hope you dont get prosecuted for dramatically improving the safety of
you and your family

NT