Cause of electrical fire

[don_resqcapt19]

The glowing connections Kwire talked about can happen at less then 1 amp of current. From what I understand, someone correct me please, some of the AFCI require 6 amp or above to work on the arc detection.

The AFCI does not look for a series arc unless the current is 5 amps or more. The AFCI does not look for a parallel arc unless the current is 75 amps or more.

 

[edlee]

AFCI can not tell the difference between a glowing connection and a resistance heater drawing same amount of current. Should a ground fault develop during the process it may trip because of ground fault feature within the AFCI device, but some don't have GF component anymore.

I understand your explanation but it seems a little bit too lab-oriented and doesn't take into account the vagaries of solid-state circuitry and power waveforms in the field. My experience of AFCI protection is that it is somewhat unreliable (in the area of false tripping) and occasionally inexplicable. It's a big beta test, as was GF protection back in the 80's, and it will take many moons for the bugs to be worked out.

If a fire started in a box because of high resistance it is entirely possible that variables would cause the wave to be affected enough that an AFCI breaker would shut off. Or maybe not. It's just speculation!

 

[GoldDigger]

The AFCI does not look for a series arc unless the current is 5 amps or more. The AFCI does not look for a parallel arc unless the current is 75 amps or more.

If the current is 75A, I would expect a normal breaker to trip too.
Or do you mean peak current, with a much lower average?

 

[don_resqcapt19]

If the current is 75A, I would expect a normal breaker to trip too.
Or do you mean peak current, with a much lower average?

As I understand it, it is the peak current and the device has to see it for a number of cycles, I think 4 out of 8 but am not sure.

Looking at the trip curve for one brand of 20 amp breaker it looks like it would have to see the 75 amp current for between 1.5 and 4 seconds before it would trip.

 

[ActionDave]

As I understand it, it is the peak current and the device has to see it for a number of cycles, I think 4 out of 8 but am not sure.

Looking at the trip curve for one brand of 20 amp breaker it looks like it would have to see the 75 amp current for between 1.5 and 4 seconds before it would trip.

Wow! Put a micro chip in a breaker and look what you get. That is one sophisticated bit of technology we are installing these days.

 

[Bladnaster]

Wow! Put a micro chip in a breaker and look what you get. That is one sophisticated bit of technology we are installing these days.

I agree. Seems like this is just giving a false sense of security. I dont have to deal with them so never really looked into them, but have heard of them as being the next best thing making them sound like they pretty much guarantee protection.

Glad I'm learning about them.

 

[kwired]

I agree. Seems like this is just giving a false sense of security. I dont have to deal with them so never really looked into them, but have heard of them as being the next best thing making them sound like they pretty much guarantee protection.

Glad I'm learning about them.

The problem is the device needs to recognize every possible fault signature to protect you from every possible fault. It also needs to know when a particular signature is an intended load instead of a fault. Consumers want performance and don't want to pay for something that constantly trips for what is supposed to be a normal condition. The technology is kind of impressive, but is not by any means been perfected yet, but we are forced to use something that doesn't quite work right whether we want to or not. You have to remember the main people that pushed these into the code were the people that make them. They wanted to start getting payback on their R&D even though they still don't have all the kinks worked out yet, and it they are not in the code, they will not sell very many of them.

 

[mopowr steve]

One time found a receptacle with a faulty "bridge" I'll call it (The piece of metal between the two screws that you can break off for splitting the receptacle) it overheated and caused severe disformation of receptacle. I would have to say some manufacturers receptacles "bridge" hardly look like they could handle even 15 amps of current. Pigtails for me!

 

[kwired]

One time found a receptacle with a faulty "bridge" I'll call it (The piece of metal between the two screws that you can break off for splitting the receptacle) it overheated and caused severe disformation of receptacle. I would have to say some manufacturers receptacles "bridge" hardly look like they could handle even 15 amps of current. Pigtails for me!

That "bridge" is very short in length and has the rest of the receptacle plus attached conductors to sink heat into, you would be surprised how small of a cross section can carry 20 amps without overheating in this situation. Ever look at fuse links and how small the cross section is on some of those in certain places? Same concept except they are intended to melt under specific conditions. The small cross sections will melt quickly under high current conditions, but under slight overload, the larger adjacent areas soak up heat and give it time delay features for minor overloads.

 

[ggunn]

I understand your explanation but it seems a little bit too lab-oriented and doesn't take into account the vagaries of solid-state circuitry and power waveforms in the field. My experience of AFCI protection is that it is somewhat unreliable (in the area of false tripping) and occasionally inexplicable. It's a big beta test, as was GF protection back in the 80's, and it will take many moons for the bugs to be worked out.

If a fire started in a box because of high resistance it is entirely possible that variables would cause the wave to be affected enough that an AFCI breaker would shut off. Or maybe not. It's just speculation!

His point is that to any device mounted in a breaker box a resistive heat source like a toaster, for example, can look exactly like a glowing connection in the wall of a house. Both are static resistances producing heat from I squared R, even though one is on the counter in a thermally isolated enclosure and the other is not.

 

[Bladnaster]

The problem is the device needs to recognize every possible fault signature to protect you from every possible fault. It also needs to know when a particular signature is an intended load instead of a fault. Consumers want performance and don't want to pay for something that constantly trips for what is supposed to be a normal condition. The technology is kind of impressive, but is not by any means been perfected yet, but we are forced to use something that doesn't quite work right whether we want to or not. You have to remember the main people that pushed these into the code were the people that make them. They wanted to start getting payback on their R&D even though they still don't have all the kinks worked out yet, and it they are not in the code, they will not sell very many of them.

What you mention is a problem not only within the trade unfortunately.

Well, hopefully they will work out the kinks pretty quickly. Would not only be annoying, but would also make me feel bad if I did install these only to have them say that they should be replaced with the new and improved version because the "old" ones were faulty.

 

[kwired]

What you mention is a problem not only within the trade unfortunately.

Well, hopefully they will work out the kinks pretty quickly. Would not only be annoying, but would also make me feel bad if I did install these only to have them say that they should be replaced with the new and improved version because the "old" ones were faulty.

They already did discover that the first ones out did not do everything promised, and came up with the next generation that detects both series and parallel acring. Something tells me this will not be the last revision though, as they certainly are not a work of perfection.