on the other hand:
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http://www.joetedesco.org/JoeTedesco/Presentation1.pdfSquare D seems to have other ideas
after alot of extensive reading, it seems the whole contraversy comes down to available fault current(300a vs 500a)..The accepted fault current available for single family dwellings has widely and historically been accepted at 300A.
Now we have another study, sponsered by overdurrent device manufacturers, that claim the actual fault current available is 500A. This is the number the overcurrent manufactuers are using to sway Code making panel into demanding a listed system combination AFCI.
It seems that The UL rep did not buy that argument in the code making panel stating that once the 300a fault current is reproven for single family dwellings (worse case scenario), the rest of the data in the manufactuer's report would be faulty and the established magnetic trip ability of standard overcurrent devices with an additional ABS AFCI would be more than adequate to mitigate any arc fault problems likely to be encountered.
UL’s representative on the Code Panel voted affirmation on this action with the following comment:
“While we support the panel action, continued support is dependent upon review of additional
data that would confirm the availability of sufficient short circuit current capability at the panel of a
typical installation.
“The arc fault protection of the branch circuit will be provided by a system that includes an outlet
branch circuit AFCI, a circuit breaker having a known instantaneous trip current and a branch
circuit of a limited length and resistance to ensure that the fault current is sufficient to trip the
breaker during a parallel arcing fault at the installation point of the outlet branch circuit AFCI. The
latest UL Research Report4 takes into consideration the impact of the available current at the
panel on the acceptable length of the branch circuit home run to the first outlet. Calculation shows
that as the available current at the origin of the branch circuit varies, so does the allowable length
of the home run.
“Additional study is needed to provide data regarding the current available at the origin of the
branch circuit in a typical installation. From this data, the panel will be able to determine if
modification of the panel action should be considered at the ROC.”
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