Re: Lurking dangers
- From: "Adrian" <anca@xxxxxxxxxxx>
- Date: Mon, 23 Mar 2009 19:58:45 -0000
Graham. wrote:
"Woody" <harrogate3@xxxxxxxxxxxxxxxxx> wrote in message
news:40Hxl.43291$aR3.9683@xxxxxxxxxxxxxxxx
"Doug Paulley" <doug.paulley.lartsspammers@xxxxxxxxxxxxxxxx> wrote in
message news:6dfds4d9utbkjb4v3dm988o8r06n28ljkg@xxxxxxxxxx
On Sun, 22 Mar 2009 13:44:27 +0000, Ian Jackson
<ianREMOVETHISjackson@xxxxxxxxxxxxxxxxx> wrote:
I have worked with 'professional equipment' which had a mains
transformer. However, on the mains input, there were 0.01 (maybe
0.001?) uf capacitors from both live and neutral to chassis. If
the chassis was not earthed, if you were holding something
earthed, you could get quite an unexpected 'tickle' from it.
I have a DVD/VCR player. It doesn't have an earth connection in the
plug, so I think it's double insulated. It looks like coated
plastic. Into it is connected a Sky magic eye and into that is plugged
(naturally) a CT100-a-like patch cable (made up myself with soldered
on plugs) from the output on my sky box.
Whilst fitting the aerial plug into the magic eye. I noticed that
if I held the plug with one hand, I would get a definite "zap" from
the plastic case of the DVD (which looks like it has been coated by
electrolysis with some metal or other.) It's continuous so not
static, and doesn't happen when I'm not holding the plug.
What's going on? Is there something wrong? Especially as the DVD
isn't even earthed.
--
http://www.kingqueen.org.uk
remove .lartsspammers to email
Most hi-fi items and associated (like DVD or Blu-Ray players) are
two core and rely upon one item in the chain - usually the amp -
having the earth contact. If they didn't - i.e. there were two items
earthed - then a hum loop could occur and Joe Public would be
returning kit right left and centre as being faulty.
Mind you, they've lived on two-core cable on almost everything on the
continent for decades without problem. The only difference is that
they double-pole switch everything where we do it the cheap way.
Under fault conditions we can leave an item live when 'switched off'
which they cannot, so earthing is a convenient way of forcing some
safety.
The very first Sky Digital boxes, the Amstrad DRX100 had an earthed
chassis and a 3 core mains lead.
I think those slim Sony VTX-S750 & 760 digiboxes had 3 core mains
leads, but it's been a long time since I saw one.
No, the Sony's have 2 core mains leads, I just checked.
--
There is no god, so stop worrying and enjoy your life.
.
- References:
- Lurking dangers
- From: widgitt
- Re: Lurking dangers
- From: Graham.
- Re: Lurking dangers
- From: Bill Wright
- Re: Lurking dangers
- From: widgitt
- Re: Lurking dangers
- From: Ian Jackson
- Re: Lurking dangers
- From: Doug Paulley
- Re: Lurking dangers
- From: Woody
- Re: Lurking dangers
- From: Graham.
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