In message , "Dave Plowman (News)"
writes
So you have equipment with floating mains earths and you have earthed
equipment. A fault occurs, someone bridges the two pieces of equipment
and gets killed.

No - it earths via the screen on the connecting cable.

Which is nor rated to carry mains fault current. Besides, what's gonna
happen when you grab a bit of gear and then either attempt to plug in or
unplug a connector that was carrying mains derived leakage current via
it's screen.


If you do disconnect equipment earths in the way you've described and
someone does die you will be held accountable for their death and will
face a charge of manslaughter.

Yeh yeh... Can you give an example of where this has happened?

Search Google.

--
Clive Mitchell
http://www.bigclive.com

LSR wrote:


A small bottle of water at Gatwick Airport (after Security!) is £1.80


The buggars at Gatwick confiscated my 12.5p lighter (one of eight from
Poundland)... "because it might be a bomb Sir" Once airside I found that
they had inferior non-refillable lighters on sale for £1.25.

I feel a much, much safer citizen now that pseudo-science profiteering
has now got to make its mark on national security and Government thinking.

Steve

In message , Clive Mitchell
writes
In message , raden
writes
You NEVER disconnect the mains earth from equipment.

Well, actually ....

sometimes you do

on a scope - might be naughty, but sometimes necessary

That's an electrical workshop environment. Besides the correct
procedure is to use a mains isolation transformer where possible. These
days I use a battery powered scope.

Which were how common exactly, 20 years ago ?

--
geoff

On Mon, 09 Apr 2007 13:00:54 GMT, Steve
wrote:


The buggars at Gatwick confiscated my 12.5p lighter (one of eight from
Poundland)... "because it might be a bomb Sir" Once airside I found that
they had inferior non-refillable lighters on sale for £1.25.

I feel a much, much safer citizen now that pseudo-science profiteering
has now got to make its mark on national security and Government thinking.


You would think that being knowledgable would bring power.

In politics it doesn't, the opposite is the case.

Those who have power but not knowledge jealously guard their powers,
whilst ensuring anyone knowledgeable is kept well down the pecking
order as a potential threat.

DG

On Mon, 9 Apr 2007 13:00:54 UTC, Steve wrote:

LSR wrote:

A small bottle of water at Gatwick Airport (after Security!) is £1.80

The buggars at Gatwick confiscated my 12.5p lighter (one of eight from
Poundland)... "because it might be a bomb Sir" Once airside I found that
they had inferior non-refillable lighters on sale for £1.25.

I feel a much, much safer citizen now that pseudo-science profiteering
has now got to make its mark on national security and Government thinking.

Indeed. The most lucrative example so far is, of course, 'global
warming'.

--
The information contained in this post is copyright the
poster, and specifically may not be published in, or used by
http://www.diybanter.com

In article ,
Clive Mitchell wrote:
So you have equipment with floating mains earths and you have earthed
equipment. A fault occurs, someone bridges the two pieces of
equipment and gets killed.

No - it earths via the screen on the connecting cable.

Which is nor rated to carry mains fault current.

Depends on the value of the appliance fuse - not the plug one. Good
quality co-ax will have a screen cross sectional area at least the equal
of 0.5mm mains cable.


Besides, what's gonna
happen when you grab a bit of gear and then either attempt to plug in or
unplug a connector that was carrying mains derived leakage current via
it's screen.

Probably nothing in the average house - apart from a spark when you
connect.

If you do disconnect equipment earths in the way you've described and
someone does die you will be held accountable for their death and will
face a charge of manslaughter.

Yeh yeh... Can you give an example of where this has happened?

Search Google.

Typical.

--
*Why does the sun lighten our hair, but darken our skin?

Dave Plowman London SW
To e-mail, change noise into sound.

"Dave Plowman (News)" wrote in message
...
In article ,
Clive Mitchell wrote:
So you have equipment with floating mains earths and you have earthed
equipment. A fault occurs, someone bridges the two pieces of
equipment and gets killed.

No - it earths via the screen on the connecting cable.

Which is nor rated to carry mains fault current.

Depends on the value of the appliance fuse - not the plug one. Good
quality co-ax will have a screen cross sectional area at least the equal
of 0.5mm mains cable.


However it may not be earthed.
The screen needs to have a low impedence to earth for ac signals and not for
mains/DC.
It could be coupled using a capacitor and hence offer no protection at all.

In message , "Dave Plowman (News)"
writes
Which is nor rated to carry mains fault current.

Depends on the value of the appliance fuse - not the plug one. Good
quality co-ax will have a screen cross sectional area at least the
equal of 0.5mm mains cable.

There have been instances where audio or data cables have melted along
their entire length when high fault current has run through them.

Search Google.

Typical.

OK. I'll do it for you....

http://www.365gay.com/Newscon06/12/1...lectrocute.htm

http://blunderford.blogspot.com/2006...ctrocuted.html
(Not actually "electrocuted" obviously.)

http://www.guitarseminars.com/ubb/Fo...ML/017378.html

http://www.guitarnoise.com/forums/vi...d=7f6dd6bc696d
8498f7b32a0dd35aaca3

And loads more. A microphone makes a great electrode for human hands.

--
Clive Mitchell
http://www.bigclive.com

In article ,
dennis@home wrote:

"Dave Plowman (News)" wrote in message
...
In article , Clive Mitchell
wrote:
So you have equipment with floating mains earths and you have
earthed equipment. A fault occurs, someone bridges the two pieces
of equipment and gets killed.

No - it earths via the screen on the connecting cable.

Which is nor rated to carry mains fault current.

Depends on the value of the appliance fuse - not the plug one. Good
quality co-ax will have a screen cross sectional area at least the
equal of 0.5mm mains cable.


However it may not be earthed. The screen needs to have a low impedence
to earth for ac signals and not for mains/DC. It could be coupled using
a capacitor and hence offer no protection at all.

In which case it won't cause an earth loop so there'd be no need to remove
the mains one.

There's a hole in my bucket, dear Lisa, dear Lisa...

--
*How do they get the deer to cross at that yellow road sign?

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
Clive Mitchell wrote:
In message , "Dave Plowman (News)"
writes
Which is nor rated to carry mains fault current.

Depends on the value of the appliance fuse - not the plug one. Good
quality co-ax will have a screen cross sectional area at least the
equal of 0.5mm mains cable.

There have been instances where audio or data cables have melted along
their entire length when high fault current has run through them.

Search Google.

Typical.

OK. I'll do it for you....

http://www.365gay.com/Newscon06/12/1...lectrocute.htm

http://blunderford.blogspot.com/2006...ctrocuted.html
(Not actually "electrocuted" obviously.)

http://www.guitarseminars.com/ubb/Fo...ML/017378.html

http://www.guitarnoise.com/forums/vi...d=7f6dd6bc696d
8498f7b32a0dd35aaca3

And loads more. A microphone makes a great electrode for human hands.

FFS. The question was about domestic hi-fi - not a gig in some dodgy
premises. Where I made it perfectly clear isolating transformers should be
used. As it happens I do.

--
*Prepositions are not words to end sentences with *

Dave Plowman London SW
To e-mail, change noise into sound.

"Dave Plowman (News)" wrote in message
...
In article ,
dennis@home wrote:

"Dave Plowman (News)" wrote in message
...
In article , Clive Mitchell
wrote:
So you have equipment with floating mains earths and you have
earthed equipment. A fault occurs, someone bridges the two pieces
of equipment and gets killed.

No - it earths via the screen on the connecting cable.

Which is nor rated to carry mains fault current.

Depends on the value of the appliance fuse - not the plug one. Good
quality co-ax will have a screen cross sectional area at least the
equal of 0.5mm mains cable.


However it may not be earthed. The screen needs to have a low impedence
to earth for ac signals and not for mains/DC. It could be coupled using
a capacitor and hence offer no protection at all.

In which case it won't cause an earth loop so there'd be no need to remove
the mains one.

There's a hole in my bucket, dear Lisa, dear Lisa...

But you removed the earth last week when you had a different device
connected that did create an earth loop.

You can get a new bucket for 99p in B&Q if you can't find any straw.

In article , Clive Mitchell wrote:
There are instances when mains hum does occur due to ground loops. These
can be fixed with sensible audio cabling and on a balanced system you
can lift the screen at the signal source end of a line-level cable. For
completely awkward electronically induced hu

Sounds like the sort of techno-babble that the rig electrician (or
was it the instrument technician? Wiggly amps person, any way.) was coming
out with.
I approached the problem from a different direction - why bother
with AC mains which *might* have a hum ; why not build a DC-generator and
essentially power the system from something who's fundamental frequency is
1/[(the hours between switching the power on to the boiler, to you
switching off the boiler heater)*3600] Hz. If you hooked it up to your
central heating system (to recover the surplus heat), you could easily get
a power supply with a supply "hum" in the micro- or nano-Hertz.

Still not the right answer to someone who's decided he needs to
spend 3 grand on a power lead.

--
Aidan
Aberdeen, Scotland
Written at Tue, 10 Apr 2007 09:05 +0100, but posted later.