Sq D as combiner box [RE-wrenches]

[Eric Smiley]

>I thought all breakers were current limiting,

Calling a fuse current limiting means it limits the peak let through
current so that fuses or breakers with a lower AIR can be used
downstream.

The definition I have from Bussman is, " If a protective device cuts off
a short-circuit in less than one-half cycle, before it reaches its total
available value, the device is a "current limiting" device."

Obviously, in a DC system there are no cycles, but the main idea is that
a current limiting fuse will restrict the let through current to a value
less than the Amps Interrupt Rating / Amps Interrupt Capacity
(AIR)/(AIC) of a downstream breaker.

Fuse manufacturers publish graphs that show the let through current of a
fuse relative to the available short circuit current, but they usually
only do this for AC applications.

In general breakers don't act fast enought to limit the current to less
than the available short circuit current.

The AIR/AIC value of a fuse or breaker is the maximum available short
circuit current the device can safely interrupt without damage/rupture
etc.


----------------------------------------------------------------------
Eric Smiley
Project Leader - BCIT Technology Centre
Photovoltaic Energy Applied Research Lab (PEARL) - BCIT
ph: (604)432-8657 www.bcit.ca/~tc/pearl/index.htm

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