In article , Jeff Wisnia wrote:

What I'd like to learn is just what kind of faults and accidents drove
the code to require a separate ground conductor for those kind of
dedicated 230 volt appliance circuits, mainly clothes dryers and stoves
I suppose. By "dedicated" I mean that the circuit only serves one
receptical/appliance.

First off, note that clothes dryers and stoves are *not* purely 240V
appliances: the heating elements are 240V, but the control circuits (and, in
the case of a dryer, the motor) are 120V and thus need a neutral.

The neutral in a 120V circuit carries current. When the equipment chassis is
bonded to the neutral conductor, any person touching the chassis becomes a
secondary, parallel path to ground for the return current. Under certain
adverse circumstances (e.g. barefoot on a wet concrete floor) the possibility
exists for hazardous levels of current to flow through that person - even when
there is no fault in the wiring or in the appliance.

Wiring faults (e.g. a high-resistance connection in the neutral) greatly
increase this hazard, again even when there is no fault in the appliance.

These risks are essentially eliminated when the neutral is isolated from the
equipment chassis, and the chassis is bonded to ground.


--
Regards,
Doug Miller (alphageek at milmac dot com)

Nobody ever left footprints in the sands of time by sitting on his butt.
And who wants to leave buttprints in the sands of time?