On Tue, 25 Aug 2009 09:16:32 +0100, D.M. Procida wrote:

When plugged into one mains ring in the house, my aluminium MacBook has
a soft 50Hz tingle to it (that can be felt when brushing it lightly with
your skin).

Plugged into another, it doesn't.

Have you checked only with one socket (oe double socket if that's the case)
on each ring?

The MacBook does not have an earthed connection - only live and neutral
enter the PSU.

What's the likely explanation?

Nothing springs immediately to mind other than to ask, have you checked the
socket is wired correctly?

--
The Wanderer

That no one understands doesn't make you an artist.