grounding questions...

[neil.johnson at camcon.co.uk]

In the UK ......

If a device is "double-insulated" then external metal parts do not have to be
earthed.  For example, the Roland MKS-70 (brushed aluminium front panel) only
has a two-wire connection to the mains.  The Yamaha SY77 (wide front panel, all
metal) only has a two-wire mains lead because it is double-insulated.

Double-insulation adds an extra insulation layer between the mains and the
outside world, so no protective earth is required.  In single-insulated
equipment the earth is provided only to carry the fault current before the fuse
or trip breaks, and thats all.  For large electrical installations the earth
wire can be smaller than the main conductors because it only has to carry fault
current just long enough for the fuse to blow.

As for reduction of noise, that's another issue.

Neil
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