An electrical question about AFCIs.

[Q.E.D]

@boytyperanma

…do to…

I can’t keep my mouth shut any longer; this is about the fifth time in a couple days I’ve seen you make this error. It’s due to. D-U-E.

Okay, carry on.

[Le_Ministre_de_l_au-dela]

@gotpasswords

Not just inside walls, but inside things like extension cords or lamp cords run under rugs so they get stepped on. Crush a cord enough, and it can start arcing internally to the point that it heats up and ignites the rug/drapes/dirty laundry that’s on top of it.

Ironically, it’s because of the AFCI breaker that we have extension cords at the moment. Not under anything, mind you but they wouldn’t be there if the receptacles could be used.

[Rosetta_s_Stoned]

I think an important consideration is being missed here.
While it’s entirely possable that the AFCI is malfunctioning and needs to be replaced, it is also quite possable that it is doing exactly what it’s intended to do.
If I’m understanding this…
OP states that the only load on the entire circut is a night light. Puts an other (more substancial) load on the circuit, and it trips.
If there is a loose/bad connection, or a defective conductor anywhere in the circuit that the load has to pass through (in the walls, at a receptical, ect.), AND is causing an arc, then the Arc Fault Circuit Interupter should trip.
A wireing defect that has the potential to arc needs current (a load) to pass through it to produce an arc
If there is an arc happening in his walls, he/we should be glad the AFCI detected it.

[boytyperanma]

It is entirely possible there is an actual fault somewhere. The most reasonable course of action would be to replace the breaker as a first step. If after replacing the breaker the same problem occurs then you look for wiring issues.

[Q.E.D]

@Rosetta_s_Stoned

A wireing defect that has the potential to arc needs current (a load) to pass through it to produce an arc

Wrong, wrong, wrong. Arcs are not triggered by loads in parallel to the fault, they are triggered either by point contact at the fault location or by dielectric breakdown due to voltage.

[Rosetta_s_Stoned]

@Q.E.D

Wrong, wrong, wrong. Arcs are not triggered by loads in parallel to the fault, they are triggered either by point contact at the fault location or by dielectric breakdown due to voltage.

So current does not need to flow in order for an arc to happen?
I’m thinking of an arc in series with the load, not a short circuit arc fault.
I thought that was the reason for AFCI.

[Q.E.D]

@Rosetta_s_Stoned

So current does not need to flow in order for an arc to happen?
I’m thinking of an arc in series with the load, not a short circuit arc fault.
I thought that was the reason for AFCI.

Both. But an arc in series with the load would result in noticeably erratic and/or intermittent operation, particularly with electronics; the OP would have immediately known something was wrong.

[Rosetta_s_Stoned]

Not if the AFCI triped fast enough.

[ZenBeam]

The OP could test this with a larger load other than the ones listed in the OP. Get one from another circuit without the problem. He should be able to very easily answer this question.

[spinky]

Can someone explain how an AFCI could detect an arc in series with a load?

[Crafter_Man]

@ntucker

Can someone explain how an AFCI could detect an arc in series with a load?

An AFCI measures the current and voltage and looks for signatures that indicate an arc is occurring. Missing waveforms in the current measurement would indicate a series arc.

[Q.E.D]

@Crafter_Man

An AFCI measures the current and voltage and looks for signatures that indicate an arc is occurring. Missing waveforms in the current measurement would indicate a series arc.

The primary indicator is high-frequency oscillations. Tesla coils make use of this by driving the primary through a spark gap. The high frequency increases the efficiency which means more bang for the buck.

[Crafter_Man]

@Q.E.D

The primary indicator is high-frequency oscillations. Tesla coils make use of this by driving the primary through a spark gap. The high frequency increases the efficiency which means more bang for the buck.

I assume you’re correct for certain AFCIs; my comment was based on a different application of AFCBs. In this other application, the algorithm is simply looking for missing current waveforms. (Check out Figure 3D in U.S. Patent 7,440,245 for more info.) Due to space limitations the μP is extremely small, which meant they had to use a relatively simple algorithm for implementing the series arcing detection.

Instead of providing just one approach, I supposed I should have stated that there are a variety of methods for detecting parallel and series arcing, and the algorithms are getting more and more sophisticated.

[Q.E.D]

@Crafter_Man

Instead of providing just one approach, I supposed I should have stated that there are a variety of methods for detecting parallel and series arcing, and the algorithms are getting more and more sophisticated.

Indeed. And some of those approaches are briefly outlined here. This paragraph touches on what I was getting at:

AFCI is yet another example of an advance in solid state technology. These breakers actually monitor the waveform pattern—or signature—rather than just the magnitude of the circuit that they are feeding. When AFCIs detect a pattern similar to the blue one in Figure 2, they recognize this signature as being an arc fault. As can be seen in the figure, an arc fault is characterized by a steady, relatively low-level, high-frequency current waveform.