John. Cambridge UK wrote:
Had a similar problem recently where there was nuisance tripping about 3
times a week. Had trouble putting the RCD back online. Checked the
Earth-neutral and found a lot of leakage on a SWA exterior connection (using
a standard multimeter). Disconnected this feeling very good and no trips for
a week, then occasional trips started again. Bit the bullet and changed the
RCD - bingo, no trips now for over two months.So it can be just a faulty
RCD.

It could simply be that the old RCD was near maximum sensitivity and
the new one near minimum. A 30mA RCD *must* trip at or below 30mA
leakage but may trip all the way down to 15mA and still be within
specification.

A large installation (as ours was before I replaced consumer units and
installed multiple RCDs) may well cause nuisance tripping of a single
30mA RCD simply because of its size. Even when all insulation
resistance etc. is within specification if there's enough little bits
of leakage they will add up to something that trips the RCD,
especially on wet days and/or when a number of PCs are turned on.

--
Chris Green )

In article ,
Andrew McKay writes:
On 2 Jul 2003 17:26:53 GMT, (Andrew
Gabriel) wrote:

Up to 5 PC's and 5 monitors will be no trouble on a 30mA RCD unless

Actually I think you are wrong.

Each Class I (earthed) piece of IT equipment is allowed to leak 0.75mA.
When designing a circuit with RCD protection, you should design for a
maximum leakage of 25% of the RCD rating, 7.5mA in this case.
That makes a maximum of 10 class I (earthed) appliances, i.e. 5 PCs
and 5 monitors. (Most other separately powered PC peripherals are
Class II appliances and don't count).

A 30mA RCD will trip at a leakage current somewhere above 15mA but
less than or equal to 30mA. That gives you your 100% headroom in
the case of the most sensitive RCD sample within spec.

I recently did my C&G2381 (16th edition wiring regs) and during a
break I got into conversation with the chap running the course - a
very experienced leccy that I had a lot of respect for.

I was talking to him about wiring computer equipment and he said that
it's a known problem when multiple computers are put onto a circuit. I
don't remember the specifics now but I'm sure he said it was to do
with the way PC power supplies implement their earthing arrangments.

He is correct. The RFI suppression components cause leakage to
earth. That's not contracdicting what I said -- it's actually
explaining it.

I have multiple PCs running here no problem, however I may not be
suffering problems because I have a UPS (uninterruptible power supply)
feeding them - I don't know whether that does make a difference or
not, but I'm certainly not suffering from RCD tripping.

Depends on the way the UPS works.
By the way, hope your UPS earthing meets the 16th edition wiring regs
(which is rather non-trivial)...

Also, there are additional requirements on circuits designed for high
earth leakage, such as numbers of PCs.

--
Andrew Gabriel

"Zog The Undeniable" wrote in message
...

How many PCs do you have? More than two can cause RCDs to trip
regularly - all PC power supplies leak a bit of current.

Never heard of that before. I can have as many as 5 computers running,
occasionally more. Mine, wife's, hobby room, one on test and the last one,
being a test bed for cross checking computer cards for the one on test.

I have a 30 mA RCD and all the house sockets are on it..

Dave