[Ed_Wischmeyer]

Eleven months afterwards, the cause of the hangar fire is determined. There was an electrical short, but it was too far away from the circuit breaker to trip it. The plastic conduit was too small, so it caught fire and dripped on something flammable. That got going and ignited a Cessna 182 that burned to the ground. Meanwhile, my RV-9A at the far end of the building was coated / filled with oily soot.

I was on the mailing list of involved parties, and there were about 60 on the list. Every identifiable appliance manufacturer was on the list, and supposedly Amazon had three representatives. The expenses of the parties doing the CYA bit has got to be pretty frisky.

The RV-9A just got the last of the insurance work done (the paint) and is now ready for Oshkosh. I've flown it twice, one for an IPC, but I want to fly it some more before leaving for Oshkosh and points north on Monday. However, yesterday a truck moving an excavator whacked my preferred route to the airport, and that freeway will be closed all weekend. What's worse is that all that freeway traffic will clog all the alternate routes to the airport. Not going to explore congestion this afternoon!

 

[chaskuss]

Eleven months afterwards, the cause of the hangar fire is determined. There was an electrical short, but it was too far away from the circuit breaker to trip it. The plastic conduit was too small, so it caught fire and dripped on something flammable. That got going and ignited a Cessna 182 that burned to the ground. Meanwhile, my RV-9A at the far end of the building was coated / filled with oily soot.

I was on the mailing list of involved parties, and there were about 60 on the list. Every identifiable appliance manufacturer was on the list, and supposedly Amazon had three representatives. The expenses of the parties doing the CYA bit has got to be pretty frisky.

The RV-9A just got the last of the insurance work done (the paint) and is now ready for Oshkosh. I've flown it twice, one for an IPC, but I want to fly it some more before leaving for Oshkosh and points north on Monday. However, yesterday a truck moving an excavator whacked my preferred route to the airport, and that freeway will be closed all weekend. What's worse is that all that freeway traffic will clog all the alternate routes to the airport. Not going to explore congestion this afternoon!

Ed, I'm curious. Was the plastic conduit actually approved electrical conduit, or PVC water pipe? Did local codes allow the use of plastic conduit in was is essentially a commercial structure? Most states require metal conduit in commercial buildings. What diameter was the conduit and how many wires were run through it?

 

[Ed_Wischmeyer]

Ed, I'm curious. Was the plastic conduit actually approved electrical conduit, or PVC water pipe? Did local codes allow the use of plastic conduit in was is essentially a commercial structure? Most states require metal conduit in commercial buildings. What diameter was the conduit and how many wires were run through it?

I have no idea!

 

[chaskuss]

I have no idea!

I hope you had insurance to cover your loss. If not, I would suggest you investigate the answers to my questions.

 

[bjdecker]

Ed - G3X stuff still working?

 

[Ed_Wischmeyer]

The fire was eight months or so ago. The airplane was fully insured, the hangar contents... homeowners would cover those, but $1,000 deductible and increased premiums. Turns out that the FBO will probably be the responsible party, so easy negotiations there.The transponder and GTN650 went back to Garmin to be cleaned out of soot, just in case, and the real PITA was that they came back with all of the settings erased. All the other avionics were sealed and kept on working. Anyhow, the whole painful episode has been reported in past threads. I can find the threads, but not the thread numbers...

 

[Bill Boyd]

Trying to wrap my mind around an electrical fault that is "too far away to trip the breaker" but allows the wire to heat to ignition temperatures. Seems like the current determines the wire heating and also the behavior of the breaker.

Better minds than mine will be along to enlighten me on how this could be.

 

[rocketman1988]

Trying to wrap my mind around an electrical fault that is "too far away to trip the breaker" but allows the wire to heat to ignition temperatures. Seems like the current determines the wire heating and also the behavior of the breaker.

Better minds than mine will be along to enlighten me on how this could be.

When I was in college, a couple of students hung some Christmas lights by putting a thumbtack through the zip cord wire. It did not blow the circuit breaker but it did heat up enough to start a fire. Luckily, it was a concrete building and only burned the contents of the room.

 

[Brantel]

It can happen when the wire size is not properly upsized based on the distance to the load and voltage drop.

Now subrogation lawsuits will kick in and Ed’s underwriter will get all their money back.

 

[n82rb]

It can happen when the wire size is not properly upsized based on the distance to the load and voltage drop.

Now subrogation lawsuits will kick in and Ed’s underwriter will get all their money back.

they get their money back and ed still gets to pay higher premiums. who wins that one.........

 

[Brantel]

they get their money back and ed still gets to pay higher premiums. who wins that one.........

Exactly!!!!

 

[JonJay]

Trying to wrap my mind around an electrical fault that is "too far away to trip the breaker" but allows the wire to heat to ignition temperatures. Seems like the current determines the wire heating and also the behavior of the breaker.

Better minds than mine will be along to enlighten me on how this could be.

Not all shorts are created equal. Breakers are also not fool proof. I have seen shorts develop in such a way the circuit turns into an arc welder, and the breaker didn’t react. If proper materials and techniques are used, a short like this will typically be a non event. However, nothing is guaranteed.
Having a short a long distance from the breaker can be a factor, but there’s more to the story.
Thanks for the update Ed. Glad you’re getting it all sorted.

 

[Bill Boyd]

{Just saw JonJay's post but I'll hit "send" anyway...}

Still not following this, which is frustrating for the time being, but don't want to derail...

How much is the voltage drop from hot to neutral? All of it, all the time, regardless of load.

Conductor voltage drop plus voltage across the load will always total 120V, 240V or whatever the mains voltage is. The breaker trips because of current passing through it; voltage is not sensed by the breaker and is not in play except as the driver for current (E over R). Short circuits or overloads can heat wiring to combustion temperatures due to power being dissipated (I^2*R) in the wiring. Still not seeing how rated temps can be exceeded without a breaker trip unless the breaker is faulty or the heating is occurring in a very localized spot from a fault that is current-limited by excessive series resistance in the wiring.

Let's say that we have a 12 AWG run in the hangar and some goofball put it on a 30A breaker on it instead of a 20 (worst-case scenario). A "short" occurs (Ed's phrasing) and the total current is somehow inadequate ( 30A or less) to trip the breaker. The resistance of the wire run must be at least 4 ohms to stay under 30A, and at 1.59 ohms/1000' for 12AWG copper, it would take a 1,250 foot run (add 50% to that figure for a properly-sized 20A breaker) to total 4 ohms in the hot and neutral lengths combined (out-and-back). Who wires outlets like that? What user could tolerate the brown-out from a wiring run even half that length when trying to power a compressor or Skil saw in their hangar - and not demand the airport install adequate, higher-gauge wiring?

Surely it's just me, but something's not "adding up," and I don't think it's the length of the wiring but rather the performance of the breaker. PM me if I'm being an irritating dullard who doesn't know what he's yammering about. I know just enough "AC" to think I can wire my own out-buildings and ace the Amateur Extra - which probably makes me a danger to myself and others

{Thanks for the added perspective, JonJay - that helps me out a little. I still have lots to learn}

 

[airguy]

{Just saw JonJay's post but I'll hit "send" anyway...}

Still not following this, which is frustrating for the time being, but don't want to derail...

How much is the voltage drop from hot to neutral? All of it, all the time, regardless of load.

Conductor voltage drop plus voltage across the load will always total 120V, 240V or whatever the mains voltage is. The breaker trips because of current passing through it; voltage is not sensed by the breaker and is not in play except as the driver for current (E over R). Short circuits or overloads can heat wiring to combustion temperatures due to power being dissipated (I^2*R) in the wiring. Still not seeing how rated temps can be exceeded without a breaker trip unless the breaker is faulty or the heating is occurring in a very localized spot from a fault that is current-limited by excessive series resistance in the wiring.

Let's say that we have a 12 AWG run in the hangar and some goofball put it on a 30A breaker on it instead of a 20 (worst-case scenario). A "short" occurs (Ed's phrasing) and the total current is somehow inadequate ( 30A or less) to trip the breaker. The resistance of the wire run must be at least 4 ohms to stay under 30A, and at 1.59 ohms/1000' for 12AWG copper, it would take a 1,250 foot run (add 50% to that figure for a properly-sized 20A breaker) to total 4 ohms in the hot and neutral lengths combined (out-and-back). Who wires outlets like that? What user could tolerate the brown-out from a wiring run even half that length when trying to power a compressor or Skil saw in their hangar - and not demand the airport install adequate, higher-gauge wiring?

Surely it's just me, but something's not "adding up," and I don't think it's the length of the wiring but rather the performance of the breaker. PM me if I'm being an irritating dullard who doesn't know what he's yammering about. I know just enough "AC" to think I can wire my own out-buildings and ace the Amateur Extra - which probably makes me a danger to myself and others

{Thanks for the added perspective, JonJay - that helps me out a little. I still have lots to learn}

You are assuming a "perfect" short with essentially zero resistance, and all the heating is in the conductor to/from the short. Let say, for example, you don't have a perfect short, but you have one with 2 ohm resistance in a device somewhere. Now do the math again. How much heat is being injected into the localized area?

 

[JonJay]

You are assuming a "perfect" short with essentially zero resistance, and all the heating is in the conductor to/from the short. Let say, for example, you don't have a perfect short, but you have one with 2 ohm resistance in a device somewhere. Now do the math again. How much heat is being injected into the localized area?

That’s the basic concept, a regulated, or current limited arc that continues to conduct in that manner. Very unique set of circumstances.

 

[skylor]

You are assuming a "perfect" short with essentially zero resistance, and all the heating is in the conductor to/from the short. Let say, for example, you don't have a perfect short, but you have one with 2 ohm resistance in a device somewhere. Now do the math again. How much heat is being injected into the localized area?

Even if you had a 2 ohm short and 40V of voltage drop in the circuit wiring itself, the short would still draw 40 amps which should quickly trip a breaker, assuming standard 120VAC breaker sizes.

Arc faults typically are not an issue inside conducted wiring (even plastic conduit) but usually create problems on external circuit wires (appliance and lamp cords) where they can come in contact with combustible materials. This is why residential wiring codes now require arc-fault interrupters on most residential circuits.

ISkylor

 

[rocketman1988]

Even if you had a 2 ohm short and 40V of voltage drop in the circuit wiring itself, the short would still draw 40 amps which should quickly trip a breaker, assuming standard 120VAC breaker sizes.

Arc faults typically are not an issue inside conducted wiring (even plastic conduit) but usually create problems on external circuit wires (appliance and lamp cords) where they can come in contact with combustible materials. This is why residential wiring codes now require arc-fault interrupters on most residential circuits.

ISkylor

Don’t know where you live but arc fault breakers are only required on certain circuits in Indiana.

Oh, and those breakers suck, they are known for an excessive number of nuisance trips.

 

[skylor]

Don’t know where you live but arc fault breakers are only required on certain circuits in Indiana.

Oh, and those breakers suck, they are known for an excessive number of nuisance trips.

2021 NEC requires them for almost everything in residential circuits now, but many locales may not have adopted the 2021 codes yet.

I’ve read about the nuisance trip issues. I recently did a panel upgrade (7 months now) and I’ve had zero issues with SquareD QO combination arc-fault/GFCI breakers.

Skylor

 

[rocketman1988]

2021 NEC requires them for almost everything in residential circuits now, but many locales may not have adopted the 2021 codes yet.

I’ve read about the nuisance trip issues. I recently did a panel upgrade (7 months now) and I’ve had zero issues with SquareD QO combination arc-fault/GFCI breakers.

Skylor

It seems that Cutler Hammer is popular in my area. We only have two or three circuits that are arc fault and we get numerous nuisance trips.

 

[leok]

Basically it is a heat flow question. If a (partial) short draws less power than the breaker needs to trip, it becomes a question of heat dissipation. If the short heats faster than the heat dissipates, the area will continue to heat until the heat flux equals the energy input or the combustion temp is reached. A wire in a conduit will retain the heat longer than a bare wire.

 

[Kyle Boatright]

I coulda used an arc fault breaker in my garage a few years ago. One evening I was out there working on the -10 and got a whiff of "hot electrical stuff". I ended up noticing a wisp of brown residue on an outlet cover and when I bent down to investigate, I could see a wire glowing inside the outlet box. Whoever'd installed that outlet had used the "stab" connection as opposed to the screw down terminal connection and the stab connection had worked loose, creating an arc. Yikes. I immediately pulled the breaker and fixed the issue, but that's the kind of thing that'll start a fire and burn down your home or business.

 

[Mel]

I coulda used an arc fault breaker in my garage a few years ago. One evening I was out there working on the -10 and got a whiff of "hot electrical stuff". I ended up noticing a wisp of brown residue on an outlet cover and when I bent down to investigate, I could see a wire glowing inside the outlet box. Whoever'd installed that outlet had used the "stab" connection as opposed to the screw down terminal connection and the stab connection had worked loose, creating an arc. Yikes. I immediately pulled the breaker and fixed the issue, but that's the kind of thing that'll start a fire and burn down your home or business.

My first "new" house built in 1968 had aluminum wiring and "stab" connections. I had a lot of fun "fixing" that house!

 

[rv7boy]

Arc fault…I had one at my house about 15 years ago. We thought we had a dead mouse in a bathroom wall. After enduring the odor for a day or so, I found the source. About six inches of the insulation on the “hot” wire had melted, and the wire had charred the 2x4 wooden stud in the wall! If we had not been home, our house might have burned and we would have never known why. It was right beside my sink and the most used outlet in the house as measured by plug-in/ plug-out cycles, mostly recharging batteries, etc. It appeared to me that the receptacle contact had worn to the point that we sometimes had an arcing situation with the plug inserted. The wire in addition to conducting electrical energy, had conducted heat. The copper wire had that “patina” look, as if it had been “red hot.” Scary stuff! It was protected by a GFCI but I also needed an Arc Fault Circuit Breaker. More people need to know about the possibility of this occurring.

 

[MacCool]

Arc fault…I had one at my house about 15 years ago. We thought we had a dead mouse in a bathroom wall. After enduring the odor for a day or so, I found the source. About six inches of the insulation on the “hot” wire had melted, and the wire had charred the 2x4 wooden stud in the wall! If we had not been home, our house might have burned and we would have never known why. It was right beside my sink and the most used outlet in the house as measured by plug-in/ plug-out cycles, mostly recharging batteries, etc. It appeared to me that the receptacle contact had worn to the point that we sometimes had an arcing situation with the plug inserted. The wire in addition to conducting electrical energy, had conducted heat. The copper wire had that “patina” look, as if it had been “red hot.” Scary stuff! It was protected by a GFCI but I also needed an Arc Fault Circuit Breaker. More people need to know about the possibility of this occurring.

How does one inspect for a potential arc-fault issue? Is it possible to test for? We have an annual home electrical inspection from our home maintenance company. Outlets are all checked, panel is inspected, breakers tested (35 year old house, all CH in a 200 amp panel). Is that kind of evaluation something that would discover the risk of an arc-fault issue like this?

 

[ClayR_9A]

My homeowners insurance pays for this device to plug in and detect any potential faults. https://www.tingfire.com/
It hasn't detected any arcing in my house (good) but it did see an issue with a transformer being offline causing voltage sags after an extended power outage a couple months ago.

 

[JonJay]

How does one inspect for a potential arc-fault issue? Is it possible to test for? We have an annual home electrical inspection from our home maintenance company. Outlets are all checked, panel is inspected, breakers tested (35 year old house, all CH in a 200 amp panel). Is that kind of evaluation something that would discover the risk of an arc-fault issue like this?

I doubt it. Typical checks are probably done with a plug in receptacle tester and they are just testing for proper wiring, neutral, hot, and ground are correct.
Unless they take the cover off each receptacle and physically exam the terminals for evidence of overheating, it won’t show that things have been arcing.
I have had similar experiences as others. We moved a row of file cabinets for a small remodel. A long abandoned receptacle had black streaks of soot up the wall. Lucky the whole building didn’t burn down as well.
The only way you can tell if an arc may be eminent is by physical inspection, and that will only show you that things are ok now. You could still have a marginal connection or bad device somewhere that just hasn’t presented itself.
UL tests devices and boxes. A UL listed junction or box is supposed to “contain” the fire. A device is supposed to fail open. But nothing is perfect.

 

[MacCool]

I doubt it. Typical checks are probably done with a plug in receptacle tester and they are just testing for proper wiring, neutral, hot, and ground are correct.
Unless they take the cover off each receptacle and physically exam the terminals for evidence of overheating, it won’t show that things have been arcing.
I have had similar experiences as others. We moved a row of file cabinets for a small remodel. A long abandoned receptacle had black streaks of soot up the wall. Lucky the whole building didn’t burn down as well.
The only way you can tell if an arc may be eminent is by physical inspection, and that will only show you that things are ok now. You could still have a marginal connection or bad device somewhere that just hasn’t presented itself.
UL tests devices and boxes. A UL listed junction or box is supposed to “contain” the fire. A device is supposed to fail open. But nothing is perfect.

I think I'll give them a call and talk to the electrician to get more info on the testing. It will also give me a chance to ask about arc faults and get advice about testing for the issue.

 

[JonJay]

I think I'll give them a call and talk to the electrician to get more info on the testing. It will also give me a chance to ask about arc faults and get advice about testing for the issue.

Let us know what they say.

 

[Ed_Wischmeyer]

The latest word is that the fire started an hour after somebody put their airplane away and used the electric motor to lower the door.

That's all I know. Warning: smart answers for dumb questions.

 

[Ed_Wischmeyer]

Okay, here's the final word from my very pleasant insurance adjuster. At least, the current final word. The fire started in the upholstery shop at the far end of the hangar building. (Back to theory #1). Just to cover the bases, the owner of the upholstery shop identified all of the electrical devices so that all the manufacturers could send somebody to CYA. Even Walmart sent somebody, and Amazon sent 3 folks. The mailing list of folks invited to the hangar review sessions finally grew to about 60-ish, and there have been four mass inspections of the hangar building. Inspection #5 is next week while I'm (hopefully) at Oshkosh.

I will not be thinking about them.