>
>Hi folks. I'm returning to the reflector to learn some more about amps
>before I buy a second one. I've been reading the archives and see that the
>discussion certainly has been lively!
>
>I read the original thread on Line Wiring in the archives. Very informative.
>My question is, should the ground and neutral be tied together at subpanels?
>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?
>
>It's not an idle question. Eighteen months ago, I had a subpanel installed
>by an electrician next to my motorized crankup tower. There's a dedicated
>250-foot run of 1" conduit containing four #8 insulated wires carrying the
>two phases, neutral and ground to the subpanel. The subpanel contains a
>220VAC 20A main breaker and two 110 VAC 20A surge-protecting circuit
>breakers, one for the tower motor and one for a weatherproof utility outlet
>adjacent to the subpanel. The tower and panel are in a location well
>isolated from any person other than me.
>
>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.
? As would I.
> 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,
>and it seemed like the right thing to do, but I'd like an opinion from the
>experts out there.
>
? Warning: I am not an expert. . If the tower receives a healthy
>100kA bolt, my guess is that it could Zap the protection and follow the
wiring. I would not connect the tower ground to the subpanel. Since
bolts can be in the megavolts, I would have a plug/socket/20'
service-loop at the tower to disconnect the tower from the mains during
lightning storms. The same thing goes for the coax and rotor control
cables. (Type-C RF coaxial connectors are ideal for waterproof quick
disconnects.) A friend had a 45' tower which received a direct hit. The
bolt followed the "grounded" coax shield into the house and caused damage
to pretty much everything that was plugged into an electrical outlet. .
Remember that lightning acts like VLF RF.
>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. I realized that a
>surge shunted to the neutral wire would travel back to the house to find the
>ground at the main panel, so I'm pretty sure that I tied the ground and
>neutral together at the subpanel (I can't remember now for sure -- it was a
>while ago and I'd have to trudge 250' through two feet of snow to find out)
>
>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?
>
>I'm hoping that if it is technically not correct to tie the ground and
>neutral togther at the subpanel,
In this county, that is an Electric Code requirement. The breaker panel
is the only point where earth-ground and Neutral are suppose to connect.
>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?) What
>are your opinions about the proper configuration for the subpanel, both from
>a code and lightning protection perspective? Should I disconnect the neutral
>from ground at the subpanel, remove the 110VAC surge-protecting breakers and
>just install MOVs between the three AC lines and ground?
>By the way, for protection against surges induced along the 250-foot run of
>wire, I put 200V MOVs from Polyphaser on the two hot wires and the neutral
>just after they enter the house from the conduit (hey, I've got an 87A on
>that same circuit, which justifies as much protection as possible and
>ensures that this post is not off-topic!) Sound OK?
>
Are the MOVs rated for 100kA, Dick?
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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