terry wrote:
Ah.
Just found this ............
"The AFCI is intended to prevent fire from arcs. AFCI circuit breakers
are designed to meet one of two standards as specified by UL 1699:
"branch" type or "combination" type (note: the Canadian Electrical
Code uses different terminology but similar technical requirements). A
branch type AFCI trips on 75 amperes of arcing current from the line
wire to either the neutral or ground wire. A combination type adds
series arcing detection to branch type performance. Combination type
AFCIs trip on 5 amperes of series arcing. Advanced electronics inside
an AFCI breaker detect sudden bursts of electrical current in
milliseconds, long before a standard circuit breaker or fuse would
trip. A "combination AFCI breaker" will provide protection
against ........................... ".
Thanks anyway .............. had originally hoped someone
knowledgeable would have written ................
"Oh yes; there is an electronic chip inside each AFCI that ..........
".
Interesting that the 'combination' type also detects series arcing as
well as 'branch arcing'.
Cheers.
"Branch/Feeder" AFCI were required starting with the 2002 NEC and were
required only for bedrooms.
"Combination" type AFCIs are required since Jan 1, 2008. The 2008 NEC
also greatly expanded where the AFCI protection is required. In general
for a residence they are required where a GFCI is not required.
AFCIs are more useful in older houses, but most new houses will become
old houses.
"Branch" AFCIs are required to detect arcs at a 75A level, and commonly
actually detect at a 60A level. This will only detect a "parallel arc" -
line to neutral or ground. But they can trip much faster than a breaker,
particularly for an intermittent arc. They can't detect a "series arc",
like a loose connection, because the current will be less than 15 (or
20) amps. Note that the AFCIs installed before about 2008 will be this type.
"Combination" AFCIs (now required) detect arcs at a 5A level, and can
also detect a series arc.
AFCIs "look" at the current waveform to separate "bad" arcs from
"normal" arcs (switch opening, incandescent light bulb failing). Would
think that would not be easy at a 5A level. I kinda wonder if they use a
version of a digital signal processor.
All the AFCIs also include ground fault detection - required at a level
of 50mA (but commonly is 30mA). (This is higher than the 5mA level for
GFCIs.) The idea is that an arc in a cable (romex, extension cord) with
a ground wire present will soon produce a ground fault. Also testing has
shown there is a fairly good chance that a loose ("glowing") connection
at a grounded receptacle will eventually produce a ground fault and trip
an AFCI. Loose connections (including failing aluminum connections) may
produce plenty of heat ("glow") but not produce any arc, at least until
later in the failure.
A couple of good sources of info (if they are still there):
http://www.cpsc.gov/volstd/afci/AFCIFireTechnology.pdf
http://www.iaei.org/subscriber/magaz...gregmanche.htm
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