"bud--" wrote in message
news:bffb0$47640257$4213eac6

stuff snipped

I recently had a post where I had the same set up as the OP
(everything on the neutral bar--old 1960 panel). However, there was an
unused ground bar in the panel and an electrician recently added some
new grounds to it. I was concered that I forgot to ask him if that
ground bar was bonded to the neutral. Everyone here said most likely
the neutral had a "screw" that is hard to see that connects it to the
box, and therefore they should be bonded since the ground bar is right
on the metal box. So if that is true, then there must be current
running through the metal case, which you say is wrong. Or am I
misunderstanding your point?


There should only be current on ground wires in abnormal events. It is
permissible for that current to go from ground bar, through metal
enclosure, to the bonding screw or jumper in a service panel, to the
service panel neutral bar. The return path for the ground system may
also include metal electrical wiring boxes and metal pipes with wires in
them. Ground wires land on a ground bar, or only in a service panel on
the neutral bar (the neutral and ‘ground’ are connected together only in
a service panel).

Neutrals normally do have current on them. It is not permissible to use
any metal enclosures as part of the return path for the neutral. If a
ground bar has a direct wire connection to a neutral bar, connecting
neutral wires is still likely not permitted. The wire connection is
sized for short duration abnormal ground currents to trip a breaker, not
for long duration neutral return currents. Neutrals may land only on a
neutral bar.

If I understand correctly, the neutrals and grounds can't be attached at
different points in the panel and if they are, a large shunt wire should
connect the two so that the path of any abnormal current flow it through the
large shunt wire between the two bus bars and not the metal of the circuit
panel box.

there is a neutral coming in from the service, that should be connnected
to the ground/neutral bus in the main panel. All neutrals should be
connected to that bus, one per screw. If you don't have enough screws
add an auxiliary one, and you can add ONLY GROUNDS to the added bus bar
(note: I don't know if this is Code or not but it is a good idea) and
you should also bond it to the original ground/neutral bus bar with some
heavy gauge copper wire (also just my idea of a proper installation.)
That way even without the bonding there is NO current flowing through
the backbox unless there is a ground fault somewhere - it goes direct
from the original bus straight to the service.

I have a book that says you can connect more than one ground under a
screw BUT NOT NEUTRALS but I don't know if current codes have changed
any or not.

I don't think the code has changed anytime recently. The book is right
that the code explicitly does not allow more than one neutral in a
terminal.

The book may be right or wrong on ground wires. More than one wire in a
terminal is not permitted unless the terminal is 'UL' listed for more
than one wire (110.14-A). If more than one wire is permitted, the label
for the panel should indicate that. As gfretwell said "depending on
brand".

I suspect that since the panel was not installed into a house with grounded
outlets, the bus bar serves both neutrals and grounds. However, it's clear
that the two grounded outlets that were added were not done by an
electrician or even a talented amateur.

In any case it is a very bad idea to put more than one
neutral under a screw; if that were to happen, you'd need to shut off
the power to the whole house if you needed to remove one neutral from
the bus for whatever reason. Otherwise, you could end up with a
momentary open neutral on a live 120VAC circuit, and that can cause lots
of damage.

It would seem then, if I have to remove a neutral for any reason the main
shut off has to be used to kill all power to the panel. That's always a
good idea, even though it causes havoc with some of the VCR's and other
electronics in the house. Better than dumping 220VAC through them, I
suppose.

Thanks for your help.

--
Bobby G.