[RE-wrenches] Gray code area

[Kent Osterberg]

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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