Hello John,

Thanks for the info. My first reaction is to suggest that we
use 5 ma because we Yanks are a less hardy lot and need that
extra protection.

But if you look at the link:

http://hypertextbook.com/facts/2000/JackHsu.shtml
Electric Current Needed to Kill a Human

you'll see that 60 - 70 ma. may be a lethal dose.

My guess is that the 5 ma was chosen to be below the general
human threshold of sensation. But I have no idea why
Australia has chosen so high a threshold.

And did I read somewhere that in Europe the residential
distribution lines are nowhere grounded? A two-wire system,
I seem to recall. You don't have that kind of system in
Australia, do you John?

Regards,

Chuck

John Proctor wrote:
On 2005-02-25 12:44:20 +1100, chuck said:

Hello Eric,

Thanks for clarifying.

I believe you are correct. You are talking about high-resistance
onboard leakages that generate currents too small to be detected by
the GFI circuit or the breakers. The isolator diodes would probably
not conduct under those circumstances and a capacitor would help.

UL requires the GFI to trip at a 5 ma unbalance, so 24,000 ohms of
leakage would trip it. Actually, the isolator diodes would probably
pass 5 ma in that circuit without a capacitor. The capacitor would be
necessary when the leakage resistance was in the megohms and the
currents in the microamps.

Would rather not have that stuff flowing through my ground connections
through the water to adjacent boats, even at those low current levels.
This underscores the importance of making sure you don't have
dangerous leakages onboard in the first place. Easy enough to check,
but how many regularly test their GFIs?

We sure agree on the isolation transformer, too.

Thanks again, Eric.

Chuck


Chuck,

I am puzzled by your UL 5 ma rating.

Here in Australia we have basically two ratings. The first is for most
domestic installations an is 30 ma. The second is for hazerdous
locations including hospitals where the rating is 10 ma. There are other
higher rating RCD (Residual Current Devices) which are used in
industrial contexts (eg 60 ma) but the majority of installations are
either 30 ma. or 10 ma.

BTW I am an EE as well as a licensed Electrical Contractor.

Thanks, Wally.

Here's a link to fairly comprehensive discussion on some of
this topic:

http://www.mikeholt.com/documents/st...inal5-3-03.pdf
MultiGroundedNeutralFinal5-3-03.pdf (application/pdf Object)

A look a world-wide systems can be found he

http://www.selinc.com/techpprs/6123.pdf
REVIEW OF GROUND FAULT PROTECTION METHODS FOR GROUNDED,
UNGROUNDED ...

Chuck

WaIIy wrote:
On Fri, 25 Feb 2005 21:12:08 -0500, chuck wrote:


And did I read somewhere that in Europe the residential
distribution lines are nowhere grounded? A two-wire system,
I seem to recall. You don't have that kind of system in
Australia, do you John?

Regards,

Chuck


Here's an interesting read....

http://www.epanorama.net/documents/g...al_wiring.html