AFCI protection might have prevented 34 deaths - California

[jaggedben]

If self sustaining arcs are possible at 120 volts, why does 230.95 only apply to systems over 150 volts to ground? When that rule went into the code, the reasoning was self sustaining arcing ground faults do not exist below 150 volts to ground and so a 208Y/120 volt system does not require the ground fault protection that is required for a 480Y/277 volt system in 230.95 and various other sections of the code.

Okay, but a '*self* sustaining' arc is a different category and AC systems with NEC wiring methods are a particular subset of circumstances. Whereas when controlled by the right hands (such as mine a few years back) a stick welder can sustain an arc at a much lower voltage than 120. And 120VAC can cause arcs, and various things can sustain that even if the arcs are not 'self sustaining' ones. I was responding to what seemed like an inaccurate over-generalization.

 

[LarryFine]

Whereas when controlled by the right hands (such as mine a few years back) a stick welder can sustain an arc at a much lower voltage than 120.

Don't welders have additional components (reactors? ) that help sustain the arc?

 

[jaggedben]

Don't welders have additional components (reactors? ) that help sustain the arc?

I think in the case of a stick welder it's the chemicals in the electrode.

In the case of an arc welder, in my experience, a steady hand and the right wire feed speed are necessary. Perhaps there's more to it, but I'd say whatever that is is not sufficient. Maybe bigger ones than I've used are different.

Until you define a timescale for what 'sustained' means I think it's just handwaiving anyway.

 

[synchro]

And 120VAC can cause arcs, and various things can sustain that even if the arcs are not 'self sustaining' ones.

Don't welders have additional components (reactors? ) that help sustain the arc?

Traditional AC welders that use a transformer at 60Hz intentionally have a lot of leakage reactance (i.e., they have a high % impedance) in order to limit the amount of output current. Such a welder might have about 70-80V open circuit and ~30V when welding. The need for the leakage reactance is that an arc typically exhibits a negative resistance region within its curve of current vs. voltage (i.e. the slope dI/dV is negative). The reactance supplies a positive impedance that's larger than this negative resistance in order to stabilize the arc current at a steady level. Also, the reactance will limit the amount of current if an electrode sticks to the work.

Fundamentally, this is the same reason fluorescent and HID bulbs need a ballast.

The negative resistance of arcs was actually used to produce relatively high power continuous radio frequencies for transmitters before vacuum tubes took over. This is different from spark transmitters which could only produce short bursts of RF for telegraphy. A history of such arc transmitters is at the following link:

https://www.radioworld.com/columns-and-views/roots-of-radio/brute-force-transmitters

 

[GoldDigger]

Bbut glowing connections are not arcs and even UL says that an AFCI will not detect and clear a glowing connection. That is simply joule heating and there is nothing on the market that can detect and clear that type of fault.

Agreed. I was just covering two different topics in one post.

 

[GoldDigger]

Don't welders have additional components (reactors? ) that help sustain the arc?

Many topics in one Reply:

A DC welder can sustain an arc more easily, since it does not have to deal with recurring times of zero current.

An AC welder with superimposed RF does not have a long zero current period for the ionization to dissipate, as well as a large dV/dt.

An arc welder in which a metallic electrode is consumed is fundamentally different from an arc in dry gas, which is the typical concern in NEC scenarios. On the other hand a massive arc fault will in fact create a cloud of metallic copper which is a significant part of the danger to humans.

An arc across a partially conductive surface (like wood) is also a different animal, and leads to pyrolysis of the wood substrate and eventual ignition. In general an Arc Fault detector will not see this, as the current is too low.

 

[electrofelon]

Until you define a timescale for what 'sustained' means I think it's just handwaiving anyway.

When I hear the word "sustained arc" I am thinking arc flash conversations. Although I am not a supporter of AFCI's, I don't really see the relevance of that in terms of AFCI effectiveness or functionality.

 

[electrofelon]

.

An arc across a partially conductive surface (like wood) is also a different animal, and leads to pyrolysis of the wood substrate and eventual ignition. In general an Arc Fault detector will not see this, as the current is too low.

A situation like that was the closest thing I ever saw to an electrical caused fire. The complaint was a counter outlet not working. Underneath in the wall there was a mouse nest and they had chewed through some of the insulation, then all the nesting material, probably with the aid of all the mouse piss, became a mass of semiconductive carbonized material that would sparkle and get hot but not trip the breaker. Would have liked to put a afci breaker in and see if it caught it, but I'm not confident it would have.

 

[GoldDigger]

A situation like that was the closest thing I ever saw to an electrical caused fire. The complaint was a counter outlet not working. Underneath in the wall there was a mouse nest and they had chewed through some of the insulation, then all the nesting material, probably with the aid of all the mouse piss, became a mass of semiconductive carbonized material that would sparkle and get hot but not trip the breaker. Would have liked to put a afci breaker in and see if it caught it, but I'm not confident it would have.

Current AFCI breakers would not have tripped (except maybe on GF detection) unless there was an active load on the circuit which met the high current requirements to enable either the parallel or series arc detection. I believe it is more than 8A for series and more than the breaker trip current for parallel arcs. The parallel arc detection thus in real life only serves to allow an instantaneous trip on overcurrent instead of a thermal time delay.

 

[don_resqcapt19]

Current AFCI breakers would not have tripped (except maybe on GF detection) unless there was an active load on the circuit which met the high current requirements to enable either the parallel or series arc detection. I believe it is more than 8A for series and more than the breaker trip current for parallel arcs. The parallel arc detection thus in real life only serves to allow an instantaneous trip on overcurrent instead of a thermal time delay.

They don't look for a series arc unless the current is over 5 amps, and don't look for a parallel arc unless the current is over 75 amps.
Because of that, there were a couple of proposals that would have required verifying that you could actually get 75 amps at the remotest outlet in the dwelling, but they were rejected.

 

[electrofelon]

They don't look for a series arc unless the current is over 5 amps, and don't look for a parallel arc unless the current is over 75 amps.
Because of that, there were a couple of proposals that would have required verifying that you could actually get 75 amps at the remotest outlet in the dwelling, but they were rejected.

Seems kinda silly, I mean even a regular breaker will trip between .02 and .1 seconds at four times it's rating, so what is the point? Is the thinking the afci would trip just a little bit faster and that could make a difference in a fire event initiating?

 

[ramsy]

became a mass of semiconductive carbonized material that would sparkle and get hot but not trip the breaker. Would have liked to put a afci breaker in and see if it caught it, but I'm not confident it would have.

Always suspected that was one way AFCI's can trip without any sparks, or arcs.

Next time you replace a light fixture, with the switch off, hold bare EGC & Neutral in separate fingers of same hand.

Just like GFCI's trip Neutral to EGC, AFCI's also use the built-in Ohm meter to trip N-G, but at higher resistance, similar to that semiconductor carbon deposit you just described.

The different fingers experiment provides empirical evidence of an unpublished, and un-patented mechanism that AFCI's use to pass UL 1699.

Anyone frustrated by AFCI nuisance tripping, may also witness empirical design vulnerability to radio & electronic noise, especially with un-listed, nor FCC tested appliances from China, or sold on amazon.com

More motive for the industry to mobilize amendments to remove AFCI requirements in half the country.

 

[ptonsparky]

FWIU, not all AFCIs include ground fault detection.

 

[don_resqcapt19]

Seems kinda silly, I mean even a regular breaker will trip between .02 and .1 seconds at four times it's rating, so what is the point? Is the thinking the afci would trip just a little bit faster and that could make a difference in a fire event initiating?

The QO trip curves shows the trip time for a 4x current to be between 1.1 and 3.9 seconds.

 

[don_resqcapt19]

Always suspected that was one way AFCI's can trip without any sparks, or arcs.

Next time you replace a light fixture, with the switch off, hold bare EGC & Neutral in separate fingers of same hand.

Just like GFCI's trip Neutral to EGC, AFCI's also use the built-in Ohm meter to trip N-G, but at higher resistance, similar to that semiconductor carbon deposit you just described.

The different fingers experiment provides empirical evidence of an unpublished, and un-patented mechanism that AFCI's use to pass UL 1699.

Anyone frustrated by AFCI nuisance tripping, may also witness empirical design vulnerability to radio & electronic noise, especially with un-listed, nor FCC tested appliances from China, or sold on amazon.com

More motive for the industry to mobilize amendments to remove AFCI requirements in half the country.

All of the original branch circuit/feeder type AFCIs had a ground fault trip of about 30 mA as they could only pass all of the require trip tests by adding the GFP.

Now their are a number of brands that no longer have any GFP in their AFCIs. The first to eliminate that was GE, then one of the Eaton lines, and most recently, Siemens. Not sure about SquareD.
I think the biggest reasons were that they could eliminate some costs and without GFP, you can use two single pole AFCI breakers with a handle tie on a multiwire branch circuit.

 

[electrofelon]

The QO trip curves shows the trip time for a 4x current to be between 1.1 and 3.9 seconds.

Oops I was reading the chart wrong. Looks like it 2-10 seconds for a BR

 

[brycenesbitt]

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Hazard and Injury Data Systems: Mortality Data

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The spark hazard deaths, it's remarkable how many are from Fractal Wood equipment.
That and DIY dishwasher repair with the power on. And the occasional toddler inside HVAC equipment (how does that even happen)?