I had read once (long ago) that fribilation would occur starting at 7
or so mA in a statistical significant portion of the populace. To hear
30ma is surprising! I have several GFI outlets in my house and never
had nuisance tripping. Even with highly inductive loads I cannot see
how this will cause an imbalance of current unless there is a fault
path. Nuisance tripping can only occur if you indeed have an alternate
return path, lossy insulators, spark-overs etc.
Just my views!
Hans
______________________________ Reply Separator _________________________________
Subject: Re: (off topic) GFI history.
Author: Non-HP-chris-dupres ([email protected]) at
HP-ColSprings,mimegw5
List-Post: [email protected]
Date: 9/8/97 11:15 PM
Hi Rich and a few others on this topic.
you wrote:
<The RCCB/ELCB is all-magnetic rather than electronic.
It requires 20 mA or more to operate. The North American electronic type
built into an outlet requires only 5 mA to operate.>
In the UK we use 30mA for people protection on RCCD's, this is because the
onset of ventricular fibrilation will occur with a very high level of
probability at currents flowing around heart muscles above this. 50/60Hz
is about twice as dangerous as d.c., it being the Change of Current that
has the physiological effect, i.e. d.c. is dangerous above 60mA. (I'm
ignoring I^2R effects for this purpose). The danger is also related to the
actual time the current is flowing, and particularly relevant to the moment
in relation to the actual phase of the heart beat. I.e. it's quite
possible to be hit by lightening and just walk away, albeit with your
trousers on fire.
Electronic RCCD's are not used in the UK because of their lack of intrinsic
safety, i.e. safety is related to fallible electronic components, and also
the increased sensitivity can cause nuisance tripping when highly inductive
loads are switched on, the most common being the trip that feeds the
freezer switching off when the food gets too hot! The rationale being
that it's better to have no RC protection at all, than rely on RC
protection that may have failed.
A tuppence worth I think, certainly no more...
Chris Dupres
Surrey, UK.
