On 2006-07-15, Tom Horne, Electrician wrote:

Is it standard for a residential electrical subpanel to use its
chassis as a ground backplane? I.e. the ground from the incoming
4-wire feed terminates at a lug bolted to the back of the panel, and
the ground bar is also just bolted to the back of the panel.

It would be better practice to have all Equipment Grounding Conductors
terminate to the Grounding buss bar so as to avoid using the cabinet as
a fault current pathway.

So it sounds like the setup I describe is NEC compliant but not best
practice? Another poster pointed out that if any branch circuits are
run in metallic conduit and use the conduit as the EGC, then the panel
chassis is part of the fault current path anyway. However, I've run a
separate EGC for the circuits I've run in EMT.

The subpanel I'm using, the Square D QO132L125G, comes with a ground
bar that has no terminals for 1/0 wire and with a single lug bolted to
the chassis for the feeder ground wire. So it seems the
manufacturer's intention is to the chasis as a ground backplane.
Perhaps a better solution would be to replace the single lug with a
double lug (terminology?) and to run an appropriately sized jumper
wire directly to the ground bar?

If more than one Grounding buss bar is installed they should be
bonded to each other by running a conductor that is sized for the
largest Over Current Protective Device supplying power to that panel
between the buss bars.

Do you mean the largest size OCPD for circuits supplied _from_ that
panel, or the size of the feeder circuit OCPD supplying power _to_
that panel? Seems like it should be the former.

Cheers, Wayne