Interesting AFCI scenario

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crossman

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Southeast Texas
Was talking to some utility lineman at a code update class a couple weeks ago and they told me about an interesting occurrence.

In a new housing addition of approximately 100 homes, there were numerous complaints of tripping AFCIs throughout the neighborhood. At first, each homeowner tried to get the problems fixed through warranties and ECs.

After awhile, the homeowners got to noticing that these AFCI trips at numerous homes were occurring simultaneously, and typically, at each individual house, the trips occurred on the same phase (according to the ECs). Anywhere from 25% to 75% of the homes were affected at each occurrence of tripping.

The POCO was contacted and is currently conducting an investigation. I have not heard anymore about it.

My first reaction was "this can't be real". But I have no reason to doubt the linemen's veracity. So, I started thinking about it.... if the AFCI can react to a series fault, what if the series fault is on the line side of the breaker? Since the arc current is in series with any loads, the current is passing through the breakers to the load, so couldn't they trip on a line side series fault?

What if the problem was on the high voltage side of the multiple xfmrs feeding the homes?

Could there be some sort of "electronic meter reading" signal from POCO that is affecting the electronics in the AFCI?

Anyone have thoughts? As I said, I don't doubt that the linemen are telling the truth, and they were involved in the investigation but had not found anything out of the ordinary. I will attempt to track down the linemen to see if anything was resolved.
 
It was more than likely stray neutral current from the utilities MGN system, or any number of utility sources, that is feeding back into the premises wiring systems in these homes and causing the tripping.
 
electricmanscott said:
Not the AFCIs fault. Nope. Can't be. :roll:
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I agree. Something real happened at all these houses at the same time. Perhaps something as simple as current passing on the TV cable system through the homes.
 
crossman said:
Was talking to some utility lineman at a code update class a couple weeks ago and they told me about an interesting occurrence.

The POCO was contacted and is currently conducting an investigation. I have not heard anymore about it.
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If you get the chance, ask the POCO guys if there is a voltage regulator in the neighborhood. They are placed in some power distribution branches to counter-act demand-based voltage drop.

An EE friend of mine has told me about voltage regulators, which are basically automatically-operated tapped autotransformers. They might create arcing as they switch taps.
 

At a very basic level, what is the likelihood that all these homes have an arc fault at the same time?

Suppose it's not an arc at all, but some inability of the AFCI circuitry to reject power supply disturbances?

The ability to reject power supply variations is shown on integrated circuit data sheets as something like "common mode rejection ratio" or "differential mode rejection ratio".

If the IC has too low a rejection ratio for its application then some filtering of the IC voltage is needed, otherwise the IC may interpret power line variations as valid signals indicating a problem.

I guess this area-wide problem could also be a power line resonance problem that has been revealed by any other appliance.

This may be a very valuable clue to some unforeseen design defect in AFCIs.
 
walkerj said:
Maybe OT but everytime my power goes out, it simultaneously trips my MBR arc fault:confused: , but no others:confused:
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Maybe it's simply the loss of power itself. Does turning off the main breaker do the same thing?
 
Larry,
The AFCIs are not fail safe. The work like the old GFCIs. If the electronics fail, the power stays on and the device becomes a standard thermal magnetic breaker.
 
mdshunk said:
I agree. Something real happened at all these houses at the same time. Perhaps something as simple as current passing on the TV cable system through the homes.
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The utility current is not being imposed from the primary side of their transformers onto the AFCIs.
Sometimes people seem to miss the obvious. As Marc has stated, there could be other reasons, and the cable has done this on other housing sites.

I would definitely check the cable first.

Then as others such as Don have stated, maybe there is an issue with power and the electronics are not properly functioning.
 
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