Afci


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Old 08-11-08, 05:19 PM
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Afci

Hi:

Continuing my rewiring project. Today bought two Homeline AFCIs. Noticed they cost quite a bit more than anticipated.

Apparently they are new "combination AFCIs" not just "branch/feeder AFCIs."

Can someone explain the difference?

Thanks.
 
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Old 08-11-08, 05:35 PM
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I can't tell you the differences between the 2 technologies. However, the Code now requires the combination type.
 
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Old 08-11-08, 08:16 PM
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AFCIs have a very difficult job: differentiating between arcing faults and normal arcing that occurs in equipment such as switches and motors. It is apparently fairly easy to detect arcing current flow, but harder to tell just what sort of arc it is.

'Branch/Feeder' AFCIs would only trip on arcing faults in excess of something like 70A for a normal 20A breaker. This may sound like a lot, and a fair question is: wouldn't an ordinary 20A breaker trip in the event of a 70A arcing fault? Circuit breakers are intentionally designed to permit more current than their rating to flow for a limited amount of time, and a 20A breaker will carry 70A for perhaps 15 seconds. This is the _normal_ operation of a 20A breaker. An AFCI if it saw a 70A arc signature, would trip much more rapidly than an ordinary 20A breaker, which would simply see a 70A load.

A downside of this 70A threshold is that such AFCIs could never trip on a 'series fault', meaning an arcing fault (say through a bad connection) where the current was limited by a load. If you had say a heater drawing 15A through a bad connection, and there was arcing at the connection, then the AFCI would not trip until the fault grew to a proper 'parallel' (short circuiting) fault. The reason for this 70A threshold is that there is almost no chance of a _normal_ arcing load combined with the 70A current level.

'Combination' lower the detection threshold to about 5A. The hope is that they will be able to detect series arcs while still not tripping on the normal arcing mentioned above.

-Jon
 
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Old 08-11-08, 08:18 PM
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The new AFCI breakers are somehow tricky to describing this.

The Branch/Feeder AFCI only dected the parallel arc faults while the Combation AFCI will dected both parallel and series arc fault

here the expaination.,,

Branch/Feeder AFCI

A device intended to be installed at the origin of a branch circuit or feeder, such as at a panelboard. The branch/feeder AFCI provides for detection of arcing faults that can occur line-to-line, line-to-neutral and line-to-ground. To be able to handle shared neutral circuits (a common application in older homes), a two-pole AFCI can be used. This will accommodate the three-wire circuit arrangement used in shared neutral applications

Combination AFCI

In addition to the protection provided by the Branch Feeder AFCI, the Combination AFCI provides for series arc detection down to 5 amperes. This series arc detection is beneficial to detect lower level arcing in both branch circuits and power supply cords. Combination AFCI protection is required by the NEC® as of January 1, 2008
{ for the states with 2008 code cycle please check with your inspector for latest info due some reverison going on }


AFCI and GFCI Protection

An AFCI can be used in conjunction with GFCI protection to provide both arcing fault protection as well as 5mA ground fault (people) protection. A common way to provide both types of protection is to use an AFCI circuit breaker and a GFCI receptacle. AFCIs can also incorporate 5mA GFCI protection into the same package. This solution for AFCI and GFCI on the same circuit can be useful where the circuit design requires both types of protection or where the installer (or user) wants to have both types of protection.
Hope this will clear up some details with common question about the AFCI's


{ I may make this a sticky if get very common }

Merci,Marc
 
 

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