"DG" wrote in message
oups.com...
I'm wiring a subpanel in free standing garage.
70A circuit, on 4/3 conductor with a ground.

There is something that I don't understand:
The main panel has a bus that combinds the neutral and ground.
As I read about sub-panel wiring, the neutral and ground should be
seperate.

The seperate neutral and ground at the subpanel run to the combind bus
at the main panel, so electrically speaking, there is continuity
there..

Why wire them seperate at the subpanel?


The neutral and main grounding conductor are only permitted to be bonded in
one place; at the main panel or in the meter. If the neutral conductor in
the subpanel ever became disconnected, anything that was grounded would
become a shock hazard as the grounding conductor would now carry the neutral
current. Having them separate reduces that possibility. You will need to
purchase a separate grounding bar for your subpanel and have all of your
ground wires terminate on it. You also need to drive at least one (Two is
most likely) ground rod for the garage and connect them to the ground bar
also. If you have any metal piping in the garage it will need to be bonded
to the ground bar. Do not install the bonding jumper or bonding screw that
is furnished with the panel.


John Grabowski
http://www.mrelectrician.tv