Re: Why does laptop PSU have an earth wire?

On Tue, 21 Mar 2006 15:41:16 +0100, "John of Aix"
<j.murphy@xxxxxxxxxxxxxx> wrote:

Spiny Norman wrote:
On Tue, 21 Mar 2006 14:07:59 +0100, "John of Aix"
<j.murphy@xxxxxxxxxxxxxx> wrote:

Spiny Norman wrote:
On Tue, 21 Mar 2006 10:16:19 +0100, "John of Aix"
<j.murphy@xxxxxxxxxxxxxx> wrote:



All the french plugs I've ever had were 2 pin with an earth strip on
the edge of the plug to connect to the earth on the socket. The two
I've had for laptops were the same with a three hole connector to
the PSU. I'd assumed the earth was connected to a screen in the psu
but I've not had reason to have one stripped to find out.

There are two (or in fact three, but the third is for high amperage
things like cookers and ovens) and one has an earth connector,

I used to get kit from our french and italian sites and all the plugs
had earth strips on. Never actually seen one without it except some
travel adapters they sell over here for continental travel.

Well personaly I have never seen one small piece of equipment with a
three pin plug on it. Except in the UK of course.

They aren't 3 pin. They have 2 pins and a little earth strip on the
edge of the plug that engages a metal strip in the socket

but all
the portables and almost every other low powered equipmenet has two
and there are no more electrocutions in France than anywhere else.
This three pin (fused) giant plugs for equipment that is usually
smaller than the plug itself is absolutely needless.

Once had a health and safety officer doing a lecture on H/S. He
started waffling on about how UK plugs were safer than continental
stuff so I asked him what tests he could cite and pointed out the
design was certified for use in a lot more countries than the UK
design. Though I don't know how that hangs now since I've been out the
business over ten years.. I actually prefer the UK plugs just for the
ability to fit a fuse. It tends to give warning that something is
wrong before major damage occurs.

No that isn't really valid anymore, mains circuits now have a circuit
cutter ('déjoncteur in French, I don't know it in English) and it isn't
a giant 13 amp fuse that will save you as if you really had a problem,
the equipment would give out long before the fuse did.

We don't all have MCB (miniature circuit breakers) fitted especially
in older properties. I still have just fuse boxes in my home which was
rewired about 20 yrs ago.

You don't fit a 13 amp fuse in every plug either. Most of the plugs
have a 3 amp fuse in them. 13 amp in kettles and washing machines
etc. The PC I'm using has a 5 amp fuse in it. The monitor has a 3 amp.
I even have 2amp fuses in the drawer but I can't recall what they go
into at the moment:) The fused plug is primarily to protect the lead
but with so much equipment not having internal protection these days
they offer a modicum of protection for the equipment.

Anything that goes through a
transformer is not earthed as the transformation is done by
induction.

Lots of PSUs these days use a voltage regulator on a heatsink. No
transformer though quite scary for some users as to how hot they get
when they aren't expecting it. Had a couple brought to me to check
because of that.

Yes that is a bit of a problem, even when they aren't actually plugged
in to the final equipment (but into the socket) they still heat up but
I've noticed some more recent ones don't do that at all.

The convertor may be earthed but the equipement isn't, it usually
runs at 9-20 volts and a few milliamps, the danger is zilch.

However the OP was getting problems when powered off a mains supply. I
would be tempted to get a new PSU and cables. Only £30

Yes perhaps but I suspect he has a dirty mains system that causes
interference rather than anything else, they 'radiate' quite a lot as
you can see if you bring a portable radio close to the mains wires for
instance.

He can check that by trying another source. Maybe take it into work.
.

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