Re: arc fault breaker keeps tripping
- From: calvin@xxxxxxxxxxxxxxxxxxxxxxxx (Calvin Henry-Cotnam)
- Date: 14 Jan 2006 23:03:25 GMT
Steve Kraus (screen@xxxxxxxxxxxxxxxxxxxxxxx) said...
>
>How does the AFCI detect arcing if the current is so small (smaller than
>the instant trip level of a regular breaker)?
Arcing can occur between the hot and the neutral or between the hot and
ground. Arcs involve short bursts of high current, and it is this that is
detected for hot to neutral arcs. This would be very difficult to detect
for small levels of current, but true arcs are not small.
HOWEVER, the design of arc fault breakers take the approach that instead
of actually detecting arc current between hot and ground, ANY current
between hot and ground is BAD. By definition, current in the hot that
does not return through the neutral is a ground fault, so by using ground
fault detection, the breaker can trip if current between the hot and
neutral exceeds the GFCI rating.
"Standard" GFCI protection that is required around sinks for instance must
be capable of tripping when this current reaches about 5-6 mA. Many AFCI
breakers detect and trip on ground faults once they exceed 30 mA. Any
imbalance in the current in the hot and the neutral that is greater than
30 mA will cause it to trip because of this ground fault.
So, getting back to the original poster's issue: if the neutral were shared
between two circits on opposite hot legs, then anytime there is some load
on the other circuit, the current in the neutral and the hot on the AFCI
breaker will NOT be equal (or, at least not within 30 mA) and the breaker
will trip.
--
Calvin Henry-Cotnam
"Never ascribe to malice what can equally be explained by incompetence."
- Napoleon
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