UL 1699 (AFCIs)

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ryan_618

ryan_618

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Does anyone know for fact if the parrallel arc theshold for combination AFCIs was lowered from 75A to 5A? I know the series arc has been added, but I am hearing conflicting things on the parrallel part.

Thanks!
 
No, I don't.

I thought the technology wasn't changing, it was just that they were dropping the sensitivity down to 5A, and just doing that was going to provide the series-arcing protection.

Is there some other aspect of the "parallel versus series arcing" issue that I'm not aware of? We're always looking at the same two conductors (ungrounded and grounded), so I didn't think the actual technology was changing all that much, just the sensitivity of it.
 
Combination devices detect series arcs greater than 5A and parrallel arcs greater than x amps. On a cord and plug connected load, it is very unlikely that you will have a 5A series arc, since the current is limited by the load.

The selling point of the combination AFCIs is that it protects premises wiring as well as utilization equipment. The branch feeder type didn't protect utilization equipment. MY question is this: If it is highly unlikely to get a 5A series arc, and if the parrallel arc threshold wasn't changed from the branch feeder type, then once again the AFCIs will not do what they are supposed to do. However, if the parrallel arc threshold was lowered to 5A, they will (hopefully) do what the manufacturer's are telling us they will do.
 
So, do parallel arc signatures look different to AFCIs than series arc signatures?

I thought the ampere value was the key to detecting the series arc.
 
Ryan,
According to everything published by the AFCI people a few short years ago, there was no way to even have a series arc at 120 volts.
Don
 
What defines a series arc?

I was under the impression that I had witnessed lots of series arcs at 120volts. What would it be called when a current carrying conductor is opened up, as in a switch opening and you can here a spark or when unplugging a vacuum cleaner while running?

The current is limited because of the series load but wouldn't it still be classified an arc?


Even though the circuit supply may only be 120V opening an inductive load can generate a large voltage spike that can initiate the arc.

I had read where vacuum cleaners were often the cause of AFCI's nuisance tripping.
 
The issue is the fact that a series arc is self extinguishing at the zero crossing(at dwelling unit voltages) and a single arc of less than a 1/2 cycle will never have enough energy to cause any type of of problem on a 120 volt circuit. What is commonly called a series arc is really a high resistance connection that produces excessive heat when current flows. It really isn't an arc as there is a physical connection, maybe of very high resistance, but still a physical connection. An arc is current flow between two points without a physical connection.
Don
 
At least one manufacturer is aware of this. I e-mailed SquareD about this, and this is the response I got. -

Dear John,
Thank you for using the Schneider Electric web site. There are some models of vacuum cleaners that have problems with AFI circuits. Most are 2-speed models that are started out in high speed. We have found that starting in low speed does not trip the breaker. On single speed vacuums start out the vacuum in high carpet setting to eliminate startup surge.
Please feel free to contact us if we can assist you further.
Thank you,
Tim xxxxxxx
Product Support Specialist
 
don_resqcapt19 said:
The issue is the fact that a series arc is self extinguishing at the zero crossing(at dwelling unit voltages) and a single arc of less than a 1/2 cycle will never have enough energy to cause any type of of problem on a 120 volt circuit. What is commonly called a series arc is really a high resistance connection that produces excessive heat when current flows. It really isn't an arc as there is a physical connection, maybe of very high resistance, but still a physical connection. An arc is current flow between two points without a physical connection.
Don
Click to expand...

I am a little confused now. Are you implying that there should be no need to detect series arcs in 120V circuits?

Here is a link that talks about the potential for fires in series arcs:

http://www.iaei.org/subscriber/magazine/00_e/mcmanus.htm

(see 58.1.3)

I would think that lots of parallel arcs could also be self extinquishing each 1/2 cycle.
One issue could be when the connection is constantly or intermittently opening and closing. Thus constantly re-establishing the arc.

I could see a large potential for problems in a series arc of a highly inductive or capacitive load that has a large inrush current when first turned on. If this load were intermittently being interrupted (in a series fashion) there could be large currents flowing and lots of energy.




John said:
Dear John,
Thank you for using the Schneider Electric web site. There are some models of vacuum cleaners that have problems with AFI circuits. Most are 2-speed models that are started out in high speed. We have found that starting in low speed does not trip the breaker. On single speed vacuums start out the vacuum in high carpet setting to eliminate startup surge.
Please feel free to contact us if we can assist you further.
Thank you,
Tim xxxxxxx
Product Support Specialist
Click to expand...

This is exactly the text I read before. Isn't intersting that inrush current appears to be the cause of the tripping?

I have done lots of testing on inrush currents and viewed a lot those waveforms. They are usually pretty "clean" and continuously decaying in amplitude. They usually only last for a few cycles. Not like I would expect an arcing fault to look.

I would think that a very well done software routine could tell the difference.

But I also think it is not trivial at all and they probably need to spend a lot more time and money on more sophisticated devices to be able to differentiate between normal events and true arcing faults. Especially series arcs.
 
ELA,
Are you implying that there should be no need to detect series arcs in 120V circuits?
Click to expand...
Yes, I am saying that, in general, they don't exist. Most of what is called series arcing is a high resistance connection. The current flow through the high resistance connection makes heat. This is know as I^2R heating. If there is any physical seperation, there will be no arc. The only exception if where something is moving causing the conductors to make and break contact.
Don
 
ELA said:
But I also think it is not trivial at all and they probably need to spend a lot more time and money on more sophisticated devices to be able to differentiate between normal events and true arcing faults. Especially series arcs.
Click to expand...


Call me a skeptic, but I don't see how they can put much sophisticated signal processing into a $35 molded case circuit breaker made in Tijuana. :rolleyes:
 
I spoke with Randy Dollar and he said that they have worked it out and that the device does trip at 5 amps. I am not personal friends of Randy, but in my dealings with him he seems to be very honorable.


We shall see soon enough how these devices will actually perform.
 
Pierre C Belarge said:
I spoke with Randy Dollar and he said that they have worked it out and that the device does trip at 5 amps. I am not personal friends of Randy, but in my dealings with him he seems to be very honorable.


We shall see soon enough how these devices will actually perform.
Click to expand...

Pierre,

I do not know Randy either, but have had discussions with other test personnel and have data on AFCI combination Parallel Arc L-N ~50ma, L-G~5A, Series L,N ~5A protection trips. This is from one manufacturer and I am sure others will vary. rbj
 
Series arc at low (120) AC voltage

Series arc at low (120) AC voltage

While I understand the self quenching characteristic of an arc, 2 things contradict that. When I was young and more stupid than today, we drove nails through wood, set them in salt water for a resistor, then connected that inline with 2 D cell battery electrodes ... super arc light.

An AC arc welder "buzz box" is around 25-30V. These arcs are sustainable. While the AFCI technology may not be mature, if it could prevent fires in these cases, there might be SOME justification. Residential 120VAC will, in SOME circumstances, sustain an arc.
 
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