Drake,
The writer's of section 690 haven't covered all of the possible ways to
make a safe installation. Or all of the needs for a large system. You
should take it up with the AHJ first, but I suspect that it will be
approved. After all, the 20% rule (and now with NEC 2008 at the bottom
of the bus too) was intended to prevent overload of the bus bars. The
20% rule shouldn't apply if there aren't any loads in the panel.
Consider this possibility: you have six 3-kW inverters to install on
this 200-amp panel. Do you have six points of interconnection with the
utility on the bus bars? Or do you have one point of interconnection at
the line side of the 200-amp breaker? I think it is really the second
and I think that is what the electrical contractor was thinking. You may
need to label the panel to make it clear that it isn't for loads.
Kent Osterberg
Blue Mountain Solar
www.bluemountainsolar.com
Drake Chamberlin wrote:
We are installing a PV system where an electrical contractor left us an
easy way to interface with the grid. The contractor does extremely
clean work which exceeds NEC requirements, and the local code
authorities are very happy with him.
What he left us was a 200 A, feed through breaker box that feeds no
branch circuits. The building that the breaker box is in is fed by a
separate, commercial service. The feeder on the feed through lugs, from
the box, goes to a residence where the wiring feeds a 200 A service
disconnect breaker for a residential electrical service.
The sole purpose of the breaker box is to give us a place for the PV
input. The potential code issue is that the PV input goes over the 20%
limit. But there is no way the bus can be overloaded, since it is
protected by a 200 A breaker on the load side. Since the building is
commercial, and fed by a separate service, there would be no reason to
tap any loads from the box in question.
This doesn't look code compliant, from the wording of the NEC. Do you
think we should use the bus bar and backfeed a breaker, or tap in ahead
of the 200 A breaker to strictly meet code requirements.
Drake Chamberlin
Athens Electric
OH License 44810
CO License 3773
740-448-7328
303-328-5533
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