On Thu, 07 Aug 2003 11:29:46 +0100, Paul Burridge
wrote:


The question seems daft, but bear with me, gentlemen. Has anyone ever
had an electric shock that they feel lucky to have survived?

p.

This guy did believe it or not.

http://www.electrical-contractor.net/electrocution.htm

--

Regards,

Boris Mohar

Got Knock? - see:
Viatrack Printed Circuit Designs http://www3.sympatico.ca/borism/
Aurora, Ontario

On Sat, 9 Aug 2003 09:01:05 +0100, "Ian White, G3SEK"
wrote:


A typical household RCB will trip on a 60 or 100mA difference in supply
current surges up to 60A. That's pretty good common-mode rejection!

It's better than that. 30mA is the standard currently.
--

"I believe history will be kind to me, since I intend
to write it." - Winston Churchill

On Sat, 9 Aug 2003 09:01:05 +0100, "Ian White, G3SEK"
wrote:


A typical household RCB will trip on a 60 or 100mA difference in supply
current surges up to 60A. That's pretty good common-mode rejection!

It's better than that. 30mA is the standard currently.
--

"I believe history will be kind to me, since I intend
to write it." - Winston Churchill

On Sat, 09 Aug 2003 00:15:15 GMT, Gary S. Idontwantspam@net wrote:

The example above sounds more like inductive heating.

If an ungrounded piece of metal is near an RF energized coil, a
current is induced in it which heats it up. Somewhat similar to a
microwave oven.

I don't see how it can be. The metal in this case was only hot whilst
the RF was flying about. It was cold to the touch the second the power
was cut. If it takes no time to cool down I infer there's something
more to it.
--

"I believe history will be kind to me, since I intend
to write it." - Winston Churchill

On Sat, 09 Aug 2003 00:15:15 GMT, Gary S. Idontwantspam@net wrote:

The example above sounds more like inductive heating.

If an ungrounded piece of metal is near an RF energized coil, a
current is induced in it which heats it up. Somewhat similar to a
microwave oven.

I don't see how it can be. The metal in this case was only hot whilst
the RF was flying about. It was cold to the touch the second the power
was cut. If it takes no time to cool down I infer there's something
more to it.
--

"I believe history will be kind to me, since I intend
to write it." - Winston Churchill

On Fri, 8 Aug 2003 18:25:06 -0500, "john graesser"
wrote:

That wasn't the scariest
shock event in my life, I was driving down the highway, and felt the hair
raise up on my arms. Then there was a boom and my car radio stopped working.
That was the one time that I was in a lightning event.

For a moment there I thought you were about to tell us you were
abducted by aliens. :-)
--

"I believe history will be kind to me, since I intend
to write it." - Winston Churchill

On Fri, 8 Aug 2003 18:25:06 -0500, "john graesser"
wrote:

That wasn't the scariest
shock event in my life, I was driving down the highway, and felt the hair
raise up on my arms. Then there was a boom and my car radio stopped working.
That was the one time that I was in a lightning event.

For a moment there I thought you were about to tell us you were
abducted by aliens. :-)
--

"I believe history will be kind to me, since I intend
to write it." - Winston Churchill

No, the GFCI doesn't need the safety ground. Like the device you're
describing, it measures the difference between the "hot" and "neutral"
wires, by running the pair together through a transformer. A GFCI is
supposed to trip in 1/40 of a second at 5 mA.

In our system, like yours, the "hot" and "neutral" wires should always
carry equal currents, and the safety ground shouldn't carry any.
However, the safety ground is sized the same as the current-carrying
conductors so it'll handle a fault current large enough to kick the
circuit breaker. Its primary function is to protect against something
like the "hot" wire making contact with a metal appliance frame, which
should be connected to the safety ground. When it comes to a GFCI, no
assumption is made about how much of the imbalance current is returned
via the safety ground and how much via the Earth or some other path.

Roy Lewallen, W7EL

Ian White, G3SEK wrote:
Paul Burridge wrote:

Ground Fault Circuit Interruptor.


How splendid! We call them Residual Current Circuit Breakers in England.


That may not be an accurate translation. As I understand it, the GFCI
requires a ground connection in order to operate, while the RCB does not.

The RCB functions on the difference between the outgoing 'live' current
and the return current in the neutral. In the British house wiring
system, those two currents should be *exactly* equal, and the difference
(the 'residual current') should be zero. Any difference at all means
something's wrong - ping - you're disconnected.

A typical household RCB will trip on a 60 or 100mA difference in supply
current surges up to 60A. That's pretty good common-mode rejection!

RCDs can also be cascaded, so an even more sensitive RCD can be used to
protect an outdoor mains socket or a workbench.

We used to have something like GFCIs over here, but changed to RCDs
because RCDs still work if the entire house ground connection has failed.

No, the GFCI doesn't need the safety ground. Like the device you're
describing, it measures the difference between the "hot" and "neutral"
wires, by running the pair together through a transformer. A GFCI is
supposed to trip in 1/40 of a second at 5 mA.

In our system, like yours, the "hot" and "neutral" wires should always
carry equal currents, and the safety ground shouldn't carry any.
However, the safety ground is sized the same as the current-carrying
conductors so it'll handle a fault current large enough to kick the
circuit breaker. Its primary function is to protect against something
like the "hot" wire making contact with a metal appliance frame, which
should be connected to the safety ground. When it comes to a GFCI, no
assumption is made about how much of the imbalance current is returned
via the safety ground and how much via the Earth or some other path.

Roy Lewallen, W7EL

Ian White, G3SEK wrote:
Paul Burridge wrote:

Ground Fault Circuit Interruptor.


How splendid! We call them Residual Current Circuit Breakers in England.


That may not be an accurate translation. As I understand it, the GFCI
requires a ground connection in order to operate, while the RCB does not.

The RCB functions on the difference between the outgoing 'live' current
and the return current in the neutral. In the British house wiring
system, those two currents should be *exactly* equal, and the difference
(the 'residual current') should be zero. Any difference at all means
something's wrong - ping - you're disconnected.

A typical household RCB will trip on a 60 or 100mA difference in supply
current surges up to 60A. That's pretty good common-mode rejection!

RCDs can also be cascaded, so an even more sensitive RCD can be used to
protect an outdoor mains socket or a workbench.

We used to have something like GFCIs over here, but changed to RCDs
because RCDs still work if the entire house ground connection has failed.

A typical household RCB will trip on a 60 or 100mA difference in supply
current surges up to 60A. That's pretty good common-mode rejection!
==========
Don't want to be pedantic but the RCDs in domestic switchboards in the UK
(at least here in Scotland ) trip at 30 mA .
I just had a look at my house's switch board made by SQUARE -D (England)
to British Standard BS5486 pt 13

In UK industry I have come across RCDs which trip at 100 mA

Frank GM0CSZ / KN6WH