Andrew Gabriel wrote:
In article ,
Dickie mint writes:
Following a thread on Sagazone (just one funny allowed!) where someone
has a ring main RCd trip out when switchong off or pulling the plug on a
computer distribution pattress. their electrician was quoted as saying :-
"there's something coming on the market to plug into to prevent the
earth leakage outing the RCD"

Apart from horrifying me that something might be available to thwart the
very reason for having an RCD, what is he on about?

The same electrician is reported as saying "when he tested the computer
and plug, the computer went to near the end of 30mA."

Max leakage for a piece of Class I (earthed) IT equipment is 0.75mA
You would need something like 40 pieces of Class I (earthed) IT
equipment to get near 30mA leakage, assuming they all leak the
max permitted. More likely, you have one faulty one.

Is that DC or AC?

By my reckoning, 10nF of live to earth capacitance will make that figure
at nice clean 50Hz sinewave. Now shove a spike on it with loads of
harmonics..

In a typical house installation there is a huge amount of inter-wire
capacitance. Every RFI filter (mandatory on just about any piece of
electronics including CFL light bulbs) probbaly adds a few nF or more..




You should design circuits with a leakage of no more than 25% of
the RCD trip rating. For a 30mA RCD, that's a design leakage of
7.5mA. That's a maximum of 10 Class I (earthed) IT appliances
per RCD. In conventional computer terms, that would be 5 PC base
units and 5 monitors. Some LCD monitors are Class II double
insulated nowadays, and in that case you could get away with 10
PC base units. Most other small computer peripherals are also
Class II double insulated and can be ignored, but larger ones
are often Class I (earthed) and need to be allowed for.

With increasing use of IT/entertainment equipment in the home
and increasing use of RCD protected circuits, provision of more
separately RCD protected socket outlet circuits should be
considered. Hanging them all off one RCD is asking for trouble.

Oh,indeed.

However one wants that 'last line of defence' of an overall RCD..and
RCBO's are bulky and expensive.

Anyway, my point was that RCD's will trip with no fault as such other
than a lot of RFI capacitors across the mains.