AFCI question

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ronaldrc

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I'm known I ask stupid questions to some in this trade.

But someones got to do it.

I ask this same question a couple years ago never did hear the answer I wanted to.

I'm sure some didn't have a clue what I was asking and others didn't know the answer for sure.

Salesman and the manufacturers will say for sure they know but has there been proof positive test to show it?

If they do they wouldn't sale as many.

The Question is how do the breakers know if the arc fault is on the load side or on the line side?

Is there a choke or high pass band rejection network on the line side that shunts and dissipates the energy being impressed on the conductor on the line side or what?

If not I would believe that a arc fault on the line side of the breaker would trip it. :)
 
I guess the obvious question is why would an AFCI react to arcs on the load side. :-?

GFCIs don't react to faults on the line side.

Breakers don't react to faults on the line side.
 
I believe that the AFCI reacts to the shape of the current waveform of the current flowing through the breaker. If the current waveform is interrupted in the fashion that indicates an arcing fault, then the breaker trips.

It seems to me that if current is flowing through the AFCI, and a series arcing fault 'upstream' of the AFCI interrupts the current flow in the appropriate fashion, then the net result would be current flow with an 'arc fault signature', and the AFCI would trip.

Breakers respond to the current flowing through them. If an upstream fault causes the appropriate current to flow through the breaker, then it will trip. Consider a standard thermal-magnetic breaker, supplying a motor load. An upstream short circuit can receive fault current _from_ the motor, which could in theory trip the breaker.

-Jon
 
Ronald why does a standard breaker not react to a short on the load side?

IMO the reason is the same for both.

While an arc on the line side of an AFCI device may introduce some 'noise' into the entire wiring system only the components in series with the arc will see all the characteristics, like current fluctuations etc.
 
The Arc fault trips from an electronic recognized fault impressed signature on the conductor.


It wouldn't matter if this fault was on the line or load side it would still be impressed on the conductor.

This might be the way it works does anyone on here know for sure?

A fault no matter how small would be a load. So could it be that a circuit in the breaker weighs the current in the fault and if it looks like a arc fault then tells the breaker to trip? This current on the other hand would not show on the line side.

Edited to say Sorry Bob that was not on purpose we posted at the same time.Bob sees it the same as I do but does anyone know this is the answer?
 
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AFCIs read the sine waveform as the current passes through the device. If it matches a known arc-fault condition, it opens. You must have an arc fault 'downstream' from the device in order for it to detect it and trip. You cannot 'induce' an arc-fault into a current path that is already flowing.

Arc fault detectors look for:
Flat "shoulders" in the current around current zero
Arcing current lower than ideal current
Voltage across the arc approaching a square wave
Voltage spikes each half cycle as the arc ignites and extinguishes
High frequency "noise"
 
ronaldrc said:
Could you please explain what you mean in more detail, that makes no sense to me :-?
Click to expand...

I mean an arc fault can only be sensed by an AFCI 'upstream". You can't 'create' and arc fault ahead of an AFCI for it to detect.
 
It seems to me that all that matters is the current that is actually flowing through the device, and that it doesn't matter if the fault is upstream or downstream if it actually changes the current flow through the device.

It seems to me that an arcing connection anywhere between the supply transformer and the final load could introduce an 'arc signature' on the current flowing through the final load, and that an AFCI designed to detect series arcs would see this fault.

On the other hand, a 'parallel arc' upstream of the AFCI would not change the current flowing through the AFCI, and would not be detected.

-Jon
 
I feel like someone else on here, Like why do I care as long as it works.

Well winnie it seems to me you don't care but on the other hand for me I do trouble shooting.

And I would like to know if I need to look beyond the load side of my AFCI
for a fault.

Maybe by slim Chance someone who helped design the breaker might give some input?

It is a legitimate question.:rolleyes:
 
winnie said:
It seems to me that all that matters is the current that is actually flowing through the device, and that it doesn't matter if the fault is upstream or downstream if it actually changes the current flow through the device.

It seems to me that an arcing connection anywhere between the supply transformer and the final load could introduce an 'arc signature' on the current flowing through the final load, and that an AFCI designed to detect series arcs would see this fault.

On the other hand, a 'parallel arc' upstream of the AFCI would not change the current flowing through the AFCI, and would not be detected.

-Jon
Click to expand...

If that's the case, one arc fault would trip every AFCI in your house, as well as everyone else who's on the same transformer as you.
 
Ronald,

I clearly missed the essence of your question.

My _guess_ seems to agree with your guess, but I am not on the inside of any manufacturer, nor have I done any tests, so I don't know. I'd be game to collaborate on building a test setup.

-Jon
 
081005-1837 EST

I tend to agree with winnie's analysis that it does not matter whether the series arc is before or after the AFCI.

480sparky:

That does not mean every AFCI will trip, only those in the series path with the arc. If you had an arc at the pole transformer, then lots of AFCIs should trip.

.
 
Winnie no problem

But everyone just thinks they work just on the load side and I have seen them trip for no found reason.

I had a dimmer switch trip one that wasn't on the circuit.It was in the same room but the lighting circuit was on the old basement circuit, when I did a rewire in the basement for a den I put the receptacles on a AFCI.

Some one knows the answer.:)
 
Bottom line is the fault has to be sensed by the breaker, hence load side. It is the breaker that clears the fault. The breaker sees it and opens itself, but is has to pass through load side. How, Ron, could it possibly open on the line side???
 
Gar

Ok maybe so, and I agree. But shouldn't the specs say or warn fault could possibly be on line feed side of this breaker? Yep that would really look good on the literature. :D


I would really like to know.:)
 
480sparky said:
winnie said:
It seems to me that all that matters is the current that is actually flowing through the device, and that it doesn't matter if the fault is upstream or downstream if it actually changes the current flow through the device.
Click to expand...
If that's the case, one arc fault would trip every AFCI in your house, as well as everyone else who's on the same transformer as you.
Click to expand...

Not quite; I am not saying that an arcing fault on branch circuit A will cause circuit B's AFCI to trip.

What I am saying is that anything that causes sufficient current with a sufficient 'arc signature' to flow through an AFCI will cause that AFCI to trip.

The same current must flow everywhere in a circuit. A single arc _anywhere_ in series with the circuit path will cause current flowing through that circuit to have an 'arc signature'. IMHO the circuit path includes anything upstream of the AFCI that is _in series_ with the AFCI.

An arc on a _different_ branch circuit is not in series with this AFCI, and doesn't change the current flowing this circuit. But an arcing connection in the feeder to the panel is in series with the final branch circuit.

-Jon
 
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