Lightning Revisited [RE-wrenches]

[Drake Chamberlin]

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Lightning protection is an issue that is not nearly resolved to my 
satisfaction.  My logic says that if the "grounded circuit conductor" is 
bonded to large amounts of metal, that is exposed to surges, the "grounded 
circuit conductor" will become temporarily energized.

In a system that depends on ground rods, that are located on the premise, 
there will be a fairly high resistance to ground.  This would mean 
substantial potential on the "grounded circuit conductor."  (A system's 
"grounded circuit conductor" connected to the utility's "grounded circuit 
conductor" would have much less resistance).

"The circuit between the grounded and ungrounded conductors will complete 
itself through various equipment.  It would seem that a high surge on the 
grounded conductor could create damaging current in the system.

By Code, systems over 50 volts must have one current carrying conductor 
grounded.

It is often hard to avoid grounding a conductor on low voltage systems 
because of other equipment in the system that will need to be grounded.

 From the 2001 NEC Handbook:

690.41 System Grounding.

For a photovoltaic power source, one conductor of a two-wire system with a 
system voltage over 50 volts and the reference (center tap) conductor of a 
bipolar system shall be solidly grounded or shall use other methods that 
accomplish equivalent system protection in accordance with 250.4(A) and 
that utilize equipment listed and identified for the use.
Low-voltage systems that are not grounded must have overcurrent protection 
in each of the ungrounded conductors, as required by 240.21.
Other methods that employ available equipment may be used to achieve 
objectives contained in 250.2(A), thereby providing protection for the 
photovoltaic power source circuits equivalent to solid grounding. "

-Drake

At 07:52 PM 4/11/02 -0600, you wrote:
>Bill,
>I see a possible problem with your recommended solution. The separate
>structures provision also requires a separate single-point bond in each
>"structure" between grounding conductor and a grounded conductor. On the
>three-phase wild AC of many wind generators, what would be the grounded
>conductor (the equivalent of AC neutral or DC negative)? Have I missed
>something here?
>Allan at Positive NRG

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