DIYbanter - View Single Post - Why must ground & neutral be seperate in subpanel?

Doug Miller

In article .com, wrote:

Doug Miller wrote:
In article , "The Streets"
wrote:

So, what is the proper way to connect a 220v sub-panel that has a single
bus bar for neutral and ground to a main panel with the neutral bar bonded
to the ground bar?

There isn't one.

To make a Code-compliant connection, you must install a second bar so that
you
can separate the neutral and ground conductors for the various circuits to
separate busses. The neutral bus must be electrically insulated from the
ground bus and from the panel chassis, and the ground bus must *not* be
insulated from the chassis.

*Also* you must connect the subpanel to the main panel using *four*
conductors, e.g. black, red, white, and bare (or green). White goes from the
neutral bus bar in the main panel to the neutral bus bar in the subpanel.
Bare
(or green) goes from the ground bus bar in the main panel to the ground bus
bar in the subpanel. Black and red go from the two lugs on the circuit
breaker
in the main panel which feeds the sub, to the lugs on the main breaker in the
subpanel.

Thanks everyone, especially Doug for this post which spells it out
clearly. Please comment on this proposed "fix":
I run another wire back to the main panel (I'll probably use some 12/2
with ground) and attach all three conductors to the ground bar in the
main panel.

Code violation -- all conductors for a circuit must be in the same cable,
raceway, conduit, etc. You need to run a new cable, 3 conductors plus ground
as I described.

Then, at the sub panel, I will connect all grounds to the
new cable but not to the neutral bus bar.

Another violation -- you *need* a grounding bus bar in the subpanel. Among
other things, doing what you describe leaves the subpanel chassis ungrounded.

Now all grounds will be
grounded back at the main panel, and the neutral in the sub will be
isolated from the grounds and from the sub panel chassis. (as long as I
remove the grounding screw from the neutral bus bar)

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

It's time to throw all their damned tea in the harbor again.