[RE-wrenches] 1987 NEC

[R Ray Walters]

We had an early 90s system with a DCGFP(complete with 4/0 GEC:)). A ground fault on a DC load circuit caused the  GFP to lift the ground, shut the array off, but the short was still being fed by the battery and wouldn't trip the DC breaker, since negative was disconnected from ground. I thought it was fairly backwards and dangerous from what you would want to see in this situation.
I still think this requirement causes more trouble than it fixes, especially on battery based off grid systems with DC loads.
I'm looking forward to trying some of the "smart" combiner boxes to move us forward on this issue to real safety.
Since we've had DCGFP for almost 20 years, has anyone seen these actually stop a dangerous situation? My experience is that the danger continues after the DCGFP trips, but at least you know something is wrong because after a week or so, the customer calls to complain that his array isn't charging. It's a rather complicated and less than fool proof idiot light. As Kent just pointed out: the situation is actually getting more dangerous with the higher voltages being used on off grid projects.

R. Walters
ray at solarray.com
Solar Engineer




> 
>  Not openning the PV array grounded conductor means that not only is the normally grounded conductor in the PV array possibly energized (that can't be avoided), but everything else it is attached to is possibly energized. For battery based systems that includes: the battery negative terminal, battery vent fan wiring, and all dc loads. The fact that all dc loads may be energized to the potential of the PV array is troubling. Especially with the possibility now of a 600-volt PV array charging a battery system.
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> Kent Osterberg
> Blue Mountain Solar
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