>My question is, should the ground and neutral be tied together at
subpanels?
Never
>Based on the comments I read, my guess would be no -- because if there's a
>break in the neutral conductor running from the main panel to the subpanel,
>then the ground lead becomes a conductor. Right?
Correct
>I was concerned that a lightning strike on the tower could travel through
>the motor and associated wiring to the subpanel, and then to the house via
>the four AC wires in the conduit.
It will take the path of least resistance to the points with the
greatest difference in potential.
>I already had surge protectors on all the
>coax and control cables, so I installed the 110VAC surge protecting
breakers
>on each leg of the circuit and connected the tower ground system (12 8'
rods
>with 1/0 radials) to the subpanel ground lug. I can't think of any reason
>why there would be any problem connecting the tower ground to the subpanel,
The tower ground is required to be bonded to the house's grounding
electrode, but should not use the smaller #8 wire to get there. I would take
the 1/0 directly to the electrode.
>Unfortunately, the 110VAC surge protecting breakers shunt the surge to
>neutral, not to ground. I think they must have been designed to go in main
>panels where the ground and neutral are tied together.
Actually, the neutral would provide a more direct route with less
resistance back to the source than the ground.
> I realized that a
>surge shunted to the neutral wire would travel back to the house to find
the
>ground at the main panel,
Most surges are AC, and aren't attracted to ground, but rather to their
origin. A ground provides an indirect path in grounded systems.
>If I did tie them together, then I guess the primary danger would be a
break
>in the neutral conductor running from the house to the subpanel. If that
>happened, the ground lead in the conduit would carry the AC return for the
>tower motor. Luckily, it's insulated #8, just like the neutral wire, but
>that ceases to be true once the run enters the house (it's #10 bare copper
>back to the main panel.) How dangerous is it for the ground lead to carry
>the AC return and what are the specific shock hazards, both at the tower
and
>in the house?
It can be deadly. The possible scenarios are too numerous.
>I'm hoping that if it is technically not correct to tie the ground and
>neutral togther at the subpanel, that the danger inherent in that is
>outweighed by the potential safety provided by shunting lighting strikes on
>the AC lines directly to the tower ground system (wishful thinking?)
Any lightning strikes to your AC line dissipated by your tower ground
system would have to rely on that small #10 running through your house which
may melt, or start a fire due to it's small size, however, a strike to your
AC lines would be dissipated mostly by your grounding electrode since that
would be the path of least resistance.
Jim Smith, KQ6UV
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