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<font size=3>Ray:<br><br>
It is my analysis that combiner breakers (if present) will protect only
wiring upstream of the combiner -- that is, the individual string
circuits. This protection would happen if there is a fault in one
individual string (in the wiring or the modules) that allows current from
other strings, in excess of the breaker rating, to be supplied through
the breaker feeding the faulted string.<br><br>
There are two scenarios at play here:<br><br>
1. Any fault between the combiner and the feeder destination will
not trip any circuit breakers. The breakers are sized such that the
current from each individual string is less than the breaker rating (by
more than 1.56 times) and they will not open.<br><br>
2. PV GFDI protection at the destination end of a feeder will not
help. PV GFDI circuits will not remove power from a feeder and they
will open the ground-to-grounding conductor bond.<br><br>
Analyzing this further: Fault conditions are made more likely given
that PV string circuits are no longer protected by conduit. Faults
are then more likely in individual string circuits (those circuits
without conduit protection). This is most problematic at
installations with two or fewer strings, where there is no combiner, i.e.
residential installations. Statistically, residential installations
offer greater exposure to electrical fires because: occupancy occurs for
more hours per year, fire alarms and sprinklers are often not installed,
children are more often present and standards are more lenient for
residential wiring systems.<br><br>
These two facts are PVs dirty little secrets. Further innovation is
needed...<br><br>
William Miller<br><br>
<br>
At 12:22 PM 4/5/2010, you wrote:<br>
<blockquote type=cite class=cite cite>I think the 100% rating exception
is an interpretation issue. I consider the assembly to be defined as the
breaker mounted in its listed enclosure.<br>
I agree that the AFIs would add cost, but they might actually offer some
protection too. (possibly one AFI unit could offer protection for
multiple circuits?)<br>
I've never had a PV circuit breaker actually trip, except some nuisance
tripping due to faulty breakers.<br>
PV breakers seem to only offer protection for very limited situations ie,
a short in a PV wire being backfed by enough other PV circuits to trip
the breaker.<br>
It could happen, but I've never actually seen it. Even completely
shattered modules still have enough internal resistance to limit the
short circuit current to<br>
a value below the breaker trip point.<br><br>
Ray<br><br>
On Apr 4, 2010, at 11:47 PM, Kent Osterberg
wrote:</font></blockquote></body>
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