How does AFI protection work?

[olc]

(for residential 120V circuits) How does arc fault circuit protection work?
Could a AFI circuit breaker be put on a multiwire circuit that shares a neutral?
I think there may be AFI receptacles available now? Could a AFI receptacle be put on a multi-wire circuit that shares a neutral?

 

[GoldDigger]

A two pole AFCI breaker can be used with a common neutral even if the breaker has a GF trip component. The shared neutral goes through the current transformer inside the breaker along with the two hot leads.
But an AFCI receptacle does not have any way if passing through the hot wire that is not used by the receptacle.
The AFCI receptacle can be used without pass through or to pass through only one branch of the MWBC, using a dedicated neutral past the receptacle.

 

[meternerd]

(for residential 120V circuits) How does arc fault circuit protection work?

I took a code class a while back and they explained it as a curcuit that can identify the characteristics of an arcing fault and ignore switching arcs, etc. I guess they finally made the circuit small enough to fit into a breaker. Not sure if that's good news or not. I've heard of mucho problems with them.

 

[GoldDigger]

I took a code class a while back and they explained it as a curcuit that can identify the characteristics of an arcing fault and ignore switching arcs, etc. I guess they finally made the circuit small enough to fit into a breaker. Not sure if that's good news or not. I've heard of mucho problems with them.

Then you will be in a position to appreciate that however much the capabilities of small processors may have increased, the algorithms, calculations and analysis used by the breaker, or more singularly the AFCI receptacle are not nearly as sophisticated as the ones you are used to at the utility level.
That, and the use of "cost effective" parts make them more subject to false trips and less sensitive to real arcs at the same time.
Not to mention that neither GFCI nor AFCI are even theoretically capable of detecting "glowing connections" (series faults without an open arc).

 

[ggunn]

Then you will be in a position to appreciate that however much the capabilities of small processors may have increased, the algorithms, calculations and analysis used by the breaker, or more singularly the AFCI receptacle are not nearly as sophisticated as the ones you are used to at the utility level.
That, and the use of "cost effective" parts make them more subject to false trips and less sensitive to real arcs at the same time.
Not to mention that neither GFCI nor AFCI are even theoretically capable of detecting "glowing connections" (series faults without an open arc).

Designing a breaker capable of discerning between a glowing fault and a toaster on a circuit would be a good trick indeed.

 

[olc]

A two pole AFCI breaker can be used with a common neutral even if the breaker has a GF trip component. The shared neutral goes through the current transformer inside the breaker along with the two hot leads.
But an AFCI receptacle does not have any way if passing through the hot wire that is not used by the receptacle.
The AFCI receptacle can be used without pass through or to pass through only one branch of the MWBC, using a dedicated neutral past the receptacle.

Thanks. I did not know two pole AFI circuit breakers were available. It doesn't look like Square D has one but Cutler Hammer does and according to the description it is met for exactly the situation I have (existing multi wire branch circuit with shared neutral).

 

[ptonsparky]

Thanks. I did not know two pole AFI circuit breakers were available. It doesn't look like Square D has one but Cutler Hammer does and according to the description it is met for exactly the situation I have (existing multi wire branch circuit with shared neutral).

The good thing about it is, when it trips, you now have two circuits down to troubleshoot. O Joy

 

[electricalist]

Id much prefer a device that in connected to the outlet with the plate screw holes . We leave our normal breakers in. If safety is the true issue then I think the problem starts at the load, and the ground on nm the be coated same as the others. Im not saying they are a bad idea. I do think they were a very good marketing strategy. Could there be a arc detection product that mounts to each phase ground and neutral that could monitor the whole system. Or even meg the service for arc faults during rough insp. Seems better than paying for wholesalers to come up with a better product

 

[GoldDigger]

Arc fault detectors are intended to protect against wiring faults too, not just load faults. GFCIs, on the other hand, are more likely to be useful in the case of load faults.