Eiron wrote:

Don Pearce wrote:

Doesn't matter. You only connect to earth for safety.

That's not quite true. You sometimes connect to earth to eliminate hum.
I had a setup that wasn't earthed and when someone approached the microphone
it hummed; when they touched a chassis point it stopped humming.
That wasn't an earth loop but it was capacitative pickup of mains
interference as the ground of all the double-insulated kit was
floating at a hundred volts or so.

A (design ?) defect.


Modern laptop PSUs have three core mains leads

Nonsense.

so it probably doesn't happen on new kit.

Equally nonsense. The Y cap bridging the live and secondary sides is still there
(for EMC - LOL).

Graham