Re: (OT) Voltage USA- UK

["Mark Harrison \(Yahoo!\)" <mph@xxxxxxx>]

The thing to bear in mind about electrical safety is that current and
voltage play two different roles:

- Voltage determines whether you'll get a shock. If the voltage between a
live connection you accidently touch and earth is higher than
skin-conductivity voltage, then current will flow from the live to the
earth
your feet are touching.

- Current determines how much damage will be done.

In practice, either a 110V or a 230V potential difference will break skin
conductivity, so you'll get a shock.

For a healthy adult, a normal mains whack of 230V is easily survivable.
I've
had several in my time :-) On the other hand, a high-voltage, low-current
shock is also survivable. I got a high-tension bolt once which was enough
to
knock me over (and draw the attention of everyone on that floor of the
office building with the bang to see me fallen over). Fortunately, it was
because of a LOUSY static buildup, so the current was minimal.

For a young child, enough current will flow to stop the heart. This is why
you should always fit the plastic mains-socket-covers when their are kids
around. The problem isn't small fingers getting into sockets (by the time
babies are mobile, their fingers are too big.) The problem is WET fingers
(think dribble) causing a connection between the live and the finger, and
then flowing to earth via the baby. Not nice.

Earthing also explains why construction sites are more serious about 110V
than houses. In a house, you'll have a good earth connection to the
green/yellow wire on every outlet, so if your device does have a problem
connection the case with the live, there's an earth to immediately cause
current to flow (and hopefully blow the fuse.) On a construction site, you
don't have an earth, because electricity is typically delivered by portable
generators... hence there isn't the safety-net of fuse blow-out catching
99%
of problems... simply because there isn't the reliable earth with the mains
supply to make the circuit before your legs do.

As to Mike's house... the 110V supply should be safe. As Phil said, it's
less of a worry than the 230V, and I'd be willing to wager a lot of money
that Mike had it installed by someone who knew EXACTLY what they were
doing,
and did it safely.

Regards,

Mark



----- Original Message -----
From: "Nigel Giddings" <nigel.giddings@ukonline.co.uk>
To: <ukha_d@yahoogroups.com>
Sent: Sunday, January 25, 2004 9:58 PM
Subject: RE: [ukha_d] (OT) Voltage USA- UK


> I thought the whole reason we have 110v in the UK on construction
sites
> is because it is safer than normal 230v ?
>
> Nigel
>
> -----Original Message-----
> From: Phil Harris [mailto:phil@xxxxxxx]
> Sent: 25 January 2004 18:18
> To: ukha_d@yahoogroups.com
> Subject: RE: [ukha_d] (OT) Voltage USA- UK
>
>
> > I hope mike insurance company is not on this list !. This cannot
be
> safe
>
> Why not?
>
> The 110v ring is isolated from the 240v mains supply to the house in
the
> same way that the 240/110v outlet is isolated from the mains supply in
a
> bathroom and therefore *SHOULD* be safer than the 240v outlets...
>
> ...in fact I know several people who have 110v supplies around their
> houses
> to some degree or other.
>
> Phil


UK Home Automation Meet 2004 - BOOK NOW!
http://www.ukha2004.com

http://www.automatedhome.co.uk
Post message: ukha_d@yahoogroups.com
Subscribe:  ukha_d-subscribe@yahoogroups.com
Unsubscribe:  ukha_d-unsubscribe@yahoogroups.com
List owner:  ukha_d-owner@yahoogroups.com