On Sat, 2 Nov 2002, Sean Alcorn - Avion Sydney wrote:

*>But seriously though, if the US is running at 7mA and we use 30mA and
*>still see trips on refrigeration equipment, does it come down to our
*>dirty power that Roman already pointed out? Or is this simply due to
*>inherent operating characteristics of refrigeration equipment? I am
*>curious if they run refrigeration compressors through protected
*>circuits without nuisance trips in the US.

Not from the US but really dirty power can trip GFIs. A common mode AC
filter before the panel (!) will cure this. Refrigeration equipment has
on/off cycles of compressors (with lots of turn-on current), contact
arcing and all the rest, like condensation bridging insulation
temporarily. If a particular piece of equipment on a circuit causes all
the faults then it could have bad insulation. GFI trip current is between
15 and 30mA in most parts of the world. 30mA is not supposed to go
directly through someone's heart, it's the total fault current. I can
witness that up to 150mA will not start fibrillation, although it can be
very painful afterwards ;-) Maybe in the US the liability issues are
larger (i.e. someone once injured his spine by tripping on a marmalade jar
while being electrocuted with 7.2 mA of mains from a partly dismantled
electric knife with which he was trying to cut off his left ear, and sued
successfully - so the authorities decided GFI current will be 7.0mA).

Incidentally the resistance required to pass 7mA peak at 120V is about
24k, 30mA peak at 240V is under 11k. The 'hand to hand' resistance of a
normal man is usually over 50k when not wet etc. So you can't fib from
touching with both hands (at least in theory). Right now I measured 200k
between left and right hand.

Otoh there are noGFI interrupters on high voltage power supplies and
inside valved equipment ;-)

Peter

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