Nate Nagel writes:
On 10/23/2013 03:02 PM, Scott Lurndal wrote:


If the handy-box is steel, then the screws holding the brass cover plate will
be a sufficent ground. (if the handy-box itself is, as the NEC requires,
grounded independent of the device).

That's not the way code treats it... look at a "spec grade" device, it
generally is self-grounding as well, there's a brass colored clip on one
end of the yoke making a more positive connection with the screw holding
the yoke to the box. Cheaper devices won't have that but will still
definitely have a ground screw. The older devices don't have that nor
do they have a ground screw connected to the yoke. The only ground path
is provided by the yoke to box screws which isn't currently considered
sufficient. (in practice, it probably is... I'm just being pedantic here.)

If by "yoke" you are referring to the bit on the device (i.e. switch body)
that contacts the screw which holds the device into the box and is directly
connected to the grounding post on the device, that's not sufficient by
code to ground a non-grounded metal handybox. You still must, per NEC,
attach the box directly to the ground (generally by pigtailing the grounding (not grounded)
conductor feeding the box or alternatively by using listed conduit fittings
with conductive, properly grounded conduit) - you cannot rely on the grounded
device grounding the box via the screw attaching the device to the box.

A metal cover plate is sufficiently grounded by the screws (assuming they're
conductive) attaching it to the handy-box. Look at any UL-listed metal utility
cover at your local electrical aisle.