arc fault breaker arcing ???

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-marty

Senior Member
Location
Alaska
I was working on a 7 plex where three of the units have already been remodeled.

I opened the panel in one of the finished units as my project includes a new feeder to each unit.

The insulation on the 12 awg wire coming from the arc fault breaker was melted back about one inch from overheating. This wire was placed under the screw terminal but was never tightened. What else would cause this except that the wire was arcing due to excessive resistance?
 

George Stolz

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Location
Windsor, CO NEC: 2017
Occupation
Service Manager
Kinda casts a shadow of doubt over the whole technology, don't it? :lol:

At least you caught it in time.

FWIW, that breaker would not have tripped until the arcing across the bad connection exceeded 75 amps, and even then, would only have tripped if the arcing was in a pattern the breaker's circuitry would recognize.

The new Combination style AFCI's are supposed to be more sensitive, I wonder if they would detect it? I have my doubts.
 

sparky_magoo

Senior Member
Location
Reno
I went on a call to a house with dead bedroom receptacles. The house had been remodeled a year ago & AFCI breakers installed for the bedrooms. I found a loose splice behind a receptacle in the dead bedroom. Wirenuts w/out pretwisting caused the problem. The wires were burnt about ten inches above the outlet. The AFCI never tripped. There was enough heat to burn the wires, but not enough current to trip the AFCI. The test button worked. I replaced the breaker after making repairs.
 

don_resqcapt19

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Location
Illinois
Occupation
retired electrician
George,
FWIW, that breaker would not have tripped until the arcing across the bad connection exceeded 75 amps, and even then, would only have tripped if the arcing was in a pattern the breaker's circuitry would recognize.
That would still be a series arc and the currently available AFCIs do not respind to series arcs. The only way the AFCI would respond to this condition is, one, there is enough heat generated to trip the standard thermal element in the breaker, two, enough insulation is melted away so that the fault becomes a parallel fault, or three, enough insulation is melted away so that the fault becomes a ground fault and the GFP part of the AFCI opens the circuit.
Don
 

jes25

Senior Member
Location
Midwest
AFCI's only detect series arcing???????? :? . All of the problems I have run across are just that. If this is true, IMO AFCI is practically worthless.
 

tonyi

Senior Member
They can detect some hi-amp parallel arcs. Its the load limited low amp series arcs that they don't do well on.
 

George Stolz

Moderator
Staff member
Location
Windsor, CO NEC: 2017
Occupation
Service Manager
jes25 said:
AFCI's only detect series arcing???????? :? . All of the problems I have run across are just that. If this is true, IMO AFCI is practically worthless.
The other way around. They only detect parallel arcing.

The 30mA ground fault protection included is nice. Other than that, I agree with your sentiment! :D
 
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