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