T&T: Arcing fault protection

[Truelove39 at aol.com]

There are two types of what are commonly  referred to as short circuits:  the
bbolted fault" and the barcing fault."  An example of a bolted fault would
be where a hot and neutral are  mistakenly connected together; these are
usually wiring errors and are detected  and "cleared" by circuit breakers when
the
circuit is energized. The destruction  which can be caused by a bolted fault
in
the few microseconds it takes the  breaker to clear is impressive in the case
of a typical residence service  entrance. Do the same when mis-wiring a wall
outlet and the breaker  merely trips.
Worse are arcing faults, which can occur  for a prolonged period without
drawing enough current to "trip" the circuit  breaker. There are 2 types of
arcing
faults. The current flowing in the bseries  arcing fault,b such as in a
conductor connected to a load which has frayed  to the point where it breaks
and
pulls apart enough so an arc occurs, is  current-limited by the load it is
connected to. Consequently, these do not  generally create much heat.
Parallel arcing faults, which may occur  between conductors (a bshort
circuit
arcing faultb) or between a  current-carrying conductor and ground (a b
ground arcing faultb) are limited only  by the impedance of the system, that
of the
fault, and the rating of the circuit  breaker protecting the circuit. But a
typical 15 amp branch breaker will  likely not trip before a parallel arc
becomes hot enough to start a  fire.
Most of us are familiar with GFCI  breakers. Those interested in protecting
against arcing faults as well as shock  protection offered by GFCIs may wish
to
investigate the relatively new AFCI  breakers which protect against arcing
faults.
Disclaimer: I am not an electrical  engineer; I have been fortunate to have
attended some seminars which addressed  AC power distribution systems.
Regards,
John
bSeahorseb




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