[RE-wrenches] Assembly Protects Conductors?

markf at berkeleysolar.com markf at berkeleysolar.com
Fri Aug 22 13:34:44 PDT 2014


Folks,

In looking at a circuit breaker based re-combiner for the first time, I am
now pondering the meaning of the Exception below:

NEC 2014 690.8 (B) Conductor Ampacity. PV system currents shall be
considered to be continuous. Circuit conductors shall be
sized to carry not less than the larger of 690.8(B)(1) or (2).

(1) One hundred and twenty-five percent of the maximum
currents calculated in 690.8(A) before the application of
adjustment and correction factors.

Exception: Circuits containing an assembly, together with
its overcurrent device(s), that is listed for continuous operation
at 100 percent of its rating shall be permitted to be
used at 100 percent of its rating.

Just to be clear, it is only the assembly that can be used at 100 percent
of its rating. (Isc*number of strings*1.25) The conductors in the circuit
still have to be sized for continuous operation (Isc*number of
strings*1.25*1.25).

I ask because a vendor with a 100% circuit breaker re-combiner states in
their cut sheet that use of the device "allow
smaller home run cable sizes from the string combiner to the inverter". Is
anyone aware of a means by which this claim can be substantiated?

Thanks,

Mark Frye
Berkeley Solar Electric Systems





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