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

Doug Miller

In article . com, wrote:
Doug Miller wrote:
In article . com,
wrote:

But the ground is meant to protect against a short to the 'case', so if
a short happens, the ground will not be protected by the circuit
breaker---it will overheat.

The breaker will trip long before the wire will melt.

Or, I should have noted, long before the wire will get hot enough to cause any
kind of problem.

Again, Thanks for the input. To clarify what I should have written, my
plan was to tie my new cable into a ground bussbar which will be
secured to the metal of the subpanel.

That's better... but it's still a Code violation. All conductors for any
circuit are required to be in the same conduit, cable, raceway, etc.
Furthermore, Code also prohibits connecting conductors in parallel unless
they're (I believe) 2ga or larger.

The current neutral bar either
floats or is grounded depending on one screw which makes the ground
connection. I will remove that to make it float.

Correct.

Regarding the guage
and being seperate from the supply, well sometimes something is better
than nothing. 3 #12 conductors all tied to the main panel ground bus
and to the sub panel ground bus is better than the current situation.

Undoubtedly. But it's still a Code violation. If you're going to run a new
cable anyway, why not run the right thing, connect it up properly, and be done
with it?

Each #12 conductor is good for 20 Amps, so in theory my ground wire(s)
can carry 60A combined,

Doesn't matter -- Code doesn't permit it.

and it is only a 40A breaker. A lesser evil
than the current situation which has not been problematic so far
anyway.

Understood -- but you asked for the proper way of doing this. What you
propose is not.

When I shop for the bussbar I will price a length of #4 bare
copper and consider running that to the main instead.

It's still a Code violation, because it's not in the same cable as the
conductors supplying the subpanel. You need to replace the existing feed with
8-3 cable (given that you're using a 40A breaker) with ground, so that all of
the conductors are in the same cable. And you won't have any trouble finding a
lug in the main that you can connect #8 to.

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

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