Lightning Revisited [RE-wrenches]
Brad Bassett
bsbassett at earthlink.net
Fri Apr 12 21:13:52 PDT 2002
I looked up 250.32 and found that in 250.32 (A) it says "...structures
are supplied from a common AC service..." I saw no mention of DC
circuits, so am not sure of the applicability to solar and wind. I asked
around our office and the consensus was to tie all of the grounds
together, if possible, to reduce the potential for current flow in the
grounded conductor from structure to structure.
As far as grounding 3 phase. If you have a Y 3 phase there is a neutral
conductor which could be grounded. As I understand it, if you have a
Delta 3 phase you have to be very careful grounding one of the
conductors because you can get a "wild leg" or "stinger leg" where one
of the other phases becomes much higher voltage in relation to ground
and will do damage to equipment if hooked up wrong. I've heard this is
why Y 3 phase is much more common now.
Allan Sindelar 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
>
> ----- Original Message -----
> From: "Bill Brooks" <billbrooks7 at earthlink.net>
>
> > What about employing the grounding of separate structures provision in
> > NEC
> > 250-32 (2002 code)? If there is a grounded conductor, then that
> > conductor
> > should be grounded at the tower (or PV Array for PV) and at the service
> > entrance with no ground wire between them and no metalic conduit. All
> > ungrounded conductors must have surge protection (Phasor, Delta,
> > voodoo).
> > The main issue is that you cannot touch the tower or module frames while
> > touch something connected to the house. The inverter, however, is
> > working
> > with conductors that are all referenced to the same grounding system.
>
>
>
Brad Bassett
Schott Applied Power
Tumwater, WA office
bsbassett at earthlink.net
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