On Tue, 29 Dec 2015 14:57:18 -0800 (PST), trader_4
wrote:


The bottom right two-pole breaker feeds a 220V circuit wired black/white
(i.e., the safety "ground" acting as neutral for any appliance
fed from that branch)

It's actually the reverse. The neutral also serves as a ground for
old circuits installed in the days when it was permitted, prior to a
separate ground being required. A neutral was always required to
support a circuit with both 240V and 120V loads, it can't physically
work without it. The concept of requiring grounds came later.

Actually only for ranges and clothes dryers for the 40 years or so
that this exception existed but it was still never legal from a sub
panel ... for exactly the reason we are discussing.
The neutral is 5 or 6 volts above ground.
Do you really want to be laying on a concrete slab with a drill that
is putting 5 volts AC in your sweaty hands?
That is why I would really want to see a ground rod or two.
It is going to be a tingle voltage that may or may not trip the GFCI
.... if he had any.

Then we could open the "other metallic path" thing if we are still
using the old 3 wire feeder exception.