Almost a House Flambe

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kyleb

Final Approach
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Drake the Outlaw
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Saved by an RV-10.

I was doing fiberglass work on the RV-10 out in the garage tonight. I had a space heater (propane fired torpedo type) going, and was doing a bunch of sanding. I had a dust mask on and also was wearing earmuff hearing protectors (the torpedo heater is loud).

As I was sanding, I kept getting an odd smell, like a very subtle whiff of smoke. But there are lots of chemicals in the garage, a heater was running, I was wearing the dust mask, etc. so while I did look around, I didn't actively search for a problem - assuming it was caused by something I was doing or something native to the garage.

About midnight, I went to turn off the propane heater because it was getting too warm in the shop. There is no electric switch on the unit - you just unplug it from the wall. So I did, and noticed that the outlet was warm. I also noticed that the outlet cover was slightly deformed and the outlet had emitted enough heat/smoke from one of the slots on the positive side to leave a stain on the wall that ended maybe 6" up the wall.

Hmm.

So I started turning off everything on that circuit (including the garage lights) and was surprised that the Christmas tree turned off on its own as I was walking over to turn it off. (The outlets in the den are on a circuit shared with the garage outlets - they are on opposite sides of a wall). Then I went back out to the dark garage, peered down into the outlet and saw glowing wires through the slots in the receptacle. Not good.

The next step was to kill the circuit with the breaker. Luckily I'd re-mapped all of the circuits in the house a few years ago. The house used to have a bunch of unmarked breakers. Not the case anymore.

I gave the outlet a few minutes to cool and removed the outlet cover, and subsequently (after using a tester to make sure the circuit was really powered off) I pulled the outlet itself.

As it turned out, the outlet was installed using "stab" connections and the positive terminal had gone bad around the stab connection and that was the wire I saw glowing inside the outlet.

I had to cut the positive wires pretty far back to get to good insulation so I could strip the wires properly and install a new outlet. Luckily I keep a few outlets, switches, covers, wire nuts, and the like on hand for various projects, so I was able to complete the replacement in just a few minutes and without a run to Home Depot or the hardware store.

The new outlet is nice. It works without glowing or emitting smoke or anything.

So, now I have proof that working on an RV-10 project late at night will keep your house from self-immolating.

And before I called it quits for the night, I applied one more skim coat of filler to the airplane parts. You can't let minor distractions keep you from moving forward on a project....
 
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kyleb said:
As it turned out, the outlet was installed using "stab" connections and the positive terminal had gone bad around the stab connection and that was the wire I saw glowing inside the outlet.
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I wonder how long it's going to be before the stab connections are made illegal by the NEC. They're really only suitable for running a small lamp, certainly not suitable for the continuous rated power you can draw from a standard 15-amp outlet. But, when they build a new house, they seem to stab all of them because it's fast and thus cheap.

IMO, there should be no stab connections in a garage. I lost an outlet in mine too.
 
Out of curiosity, what's the amp draw on the heater? I didn't think they drew that much.
 
I have an electrician friend who hates backstab outlets and never uses them. He thinks they are a potential safety risk and are just a lazy man’s way of doing wiring.
 
Chip Sylverne said:
Out of curiosity, what's the amp draw on the heater? I didn't think they drew that much.
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Just enough to run a small fan. Maybe an amp or two.

I think the problem was probably driven by what I'll call pass-through load. The way that outlet was wired, all of the draw from downstream loads ran through the outlet. I changed that.

The bigger problem was probably a bad stab connection.
 
kyleb said:
The new outlet is nice. It works without glowing or emitting smoke or anything.
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Letting the smoke out will ruin anything electrical or electronic. That is proof enough for me that smoke is what makes them work, since the failure mode is identical to letting blood out of your body and we all know that our bodies run on blood.
 
I had a stab-in outlet go bad (while I was out of town....). Fortunately it was in an exterior outlet and the second to the last outlet on the circuit (so it only took out itself and the outlet the TV was on. Hose was built in the '60's so this was common. Replaced it with a GFI and all is well.

I've replaced most of the outlets in the house and eliminated the stab-ins. This was one of the few old ones that I hadn't found (yet).
 
Hank S said:
Letting the smoke out will ruin anything electrical or electronic. That is proof enough for me that smoke is what makes them work, since the failure mode is identical to letting blood out of your body and we all know that our bodies run on blood.
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It's actually smoke and mirrors
 
The son and grandkids of some friends of ours lost a house because of one of those outlets. The garage refrigerator was plugged into an outlet that caught fire - the kitchen was on the other side and the fire really got going on the interior side of that shared wall. They were out of town when it happened, so by the time the neighbors became aware, the interior was fully involved. That house is in the next neighborhood over from ours, and we'd see it every time we drove to and from work. We didn't find out until a couple weeks later that we had that "friend of the family" connection. The grandkids and our kids went to school together.
 
We live in a fairly modern townhouse association of which I’ve been president for a few years, as well as de facto engineer - I get pinged every time something weird happens.

We’ve had three hot outlets over the past year, amongst 16 units. No real damage but it’s starting to get concerning. I know that I’ve stopped using the stab connections on new outlets and switches, and have asked that our neighbors do so as well.
 
scottfromboston said:
We live in a fairly modern townhouse association of which I’ve been president for a few years, as well as de facto engineer - I get pinged every time something weird happens.

We’ve had three hot outlets over the past year, amongst 16 units. No real damage but it’s starting to get concerning. I know that I’ve stopped using the stab connections on new outlets and switches, and have asked that our neighbors do so as well.
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Same electrician who wired the development ?

Another source of hot outlets are electricians helpers who improperly strip the wire and nick the conductor in the process. Add a couple of years of motion from plugging things into the outlet and you can crack the copper conductor.

In some quality craftsmanship at my prior home, the electrician drove a nail right through the conductor on an outlet for the over the stove microwave.... Took only 8years to cook off.
 
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I've never backstabbed an outlet, on the other hand these days I only buy the $3.00 outlets that take backwire, which are usually much nicer outlets all around.
 
kyleb said:
14 AWG, 15 amps. I'm surprised the breaker didn't trip too. I know the breaker works because I've tripped it before (recently, actually).
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you were probably within current limits. The stab connectors can create high resistance and at some point even current within limits can cause them to overheat. thats why stab is so bad. Arcing may also not cause a breaker to blow - around here code now requires anti-arc outlet on circuits.
 
Let'sgoflying! said:
wire size?
breaker size?
curious why it didn't trip
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A bad connection is not going to increase the current in the circuit so it wouldn't trip a breaker. However, an increased resistance at that point (or very small current conducting cross section) is going to cause a hot spot (and a bit of a voltage drop). You can make a lot of heat with 10 or 15 amps at 110 volts...
 
Very similar to what happened in my shop, only the whole C/B panel smoked.
 
Let'sgoflying! said:
wire size?
breaker size?
curious why it didn't trip
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kyleb said:
14 AWG, 15 amps. I'm surprised the breaker didn't trip too. I know the breaker works because I've tripped it before (recently, actually).
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15 A * 120V = 1800 watts. If a significant percentage of that is going to heat, you can really cook something before a breaker trips.
 
flyingcheesehead said:
15 A * 120V = 1800 watts. If a significant percentage of that is going to heat, you can really cook something before a breaker trips.
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Plenty of cookplates and the like use less amperage than that... Meaning, yes, you can generate a LOT of concentrated heat with 15A. And the breakers probably give you a little leeway.
 
weilke said:
Same electrician who wired the development ?
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We learned pretty quickly (before I moved here, honestly) not to hire anyone who did the initial build.

Good point, though. I'll keep an eye open for nicked wires.
 
On the other hand, if the 15 amp breaker on the single 14 gauge circuit that was installed in 1929 with now dried out rubber and fabric insulation that goes to the kitchen keeps popping because you have multiple appliances plugged in and running - just replace the 15 amp breaker with a 30 amp breaker like the previous owners of my house did. What could possibly go wrong?
 
Capt. Geoffrey Thorpe said:
A bad connection is not going to increase the current in the circuit so it wouldn't trip a breaker. However, an increased resistance at that point (or very small current conducting cross section) is going to cause a hot spot (and a bit of a voltage drop). You can make a lot of heat with 10 or 15 amps at 110 volts...
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Ah, thanks.
My mind saw those red hot wires, thought ‘current draw’.
Can a person use V=I*R to explain a high resistance, low amp, (and heat generating) circuit?
 
Let'sgoflying! said:
You haven’t lived til you’ve seen coins in the place of fuses in an old timey panel.
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I've done that. Put a penny in the socket, then the circuit will stay live long enough for you to find the smoke!
 
Let'sgoflying! said:
Ah, thanks.
My mind saw those red hot wires, thought ‘current draw’.
Can a person use V=I*R to explain a high resistance, low amp, (and heat generating) circuit?
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The current draw was probably coming from downstream.
Power = volts * current, substitute in Ohm's law, and you get Power = I^2 * R
 
Let'sgoflying! said:
Ah, thanks.
My mind saw those red hot wires, thought ‘current draw’.
Can a person use V=I*R to explain a high resistance, low amp, (and heat generating) circuit?
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kyleb said:
I don't know the draw, but several lights, a Christmas tree, and several other items were running downstream.
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OK, here goes. The motor for the heater isn't a purely resistive load, but that really doesn't matter in this case.

V=IR, and P=VI=I^2R.

We can treat V as a fixed 120 volts. Again, I'm not going to bother with AC and RMS vs. P-P because it really doesn't matter for purposes of this explanation. If you want to be a purist, do your own damn explanation. ;)

So, we can model this circuit as a voltage source (let's say that's on the left), a ground wire along the bottom and a hot wire along the top with several resistive loads in parallel between them. Again, for simplicity, we can model it as one resistive load representing the heater at the bad outlet, and another representing the downstream loads.

Now, if it's the wire itself that is bad, we can model that as an additional resistance in the hot wire, just to the left of where it gets to the first outlet. That will reduce the voltage to our loads, but the entire current will be passing through it. Let's figure that our two loads are 240W apiece, so 2A each at 120V, meaning that we have roughly 4 amps going through the bad spot in the wire. Now, if we assume, say, an ohm is the normal resistance of that wire, if we cut its cross sectional area in half, its resistance will double. So, 4A and 2 Ohms means we're dropping 8V there, and we're losing 32 watts to heat. That may not sound like much, but touch a 40-watt incandescent bulb sometime, that's about how much heat you're generating in the bad wire! Now, to top it off, heat increases resistivity, and the more current you're drawing on that circuit the hotter that wire is going to be - We're assuming 4A here, but a 15A circuit is rated for 12A continuous, so it could be triple that, and with the increased resistivity due to heat, we have a bit of a thermal runaway situation that's only going to make it worse.

Hope that makes sense, and that I'm right. Been a while since I did something like this, and it's late. :rofl:
 
Excellent, Kent. Thank you. I too am all for non-purist explanations, so that works great.
Now I have to wonder though, getting all practical on you guys, I know - what devices could detect that unplanned resistive load, and disconnect the circuit stopping the fire? (the CB can't - it can only trip when...amp draw is excessive, correct? The CB cannot distinguish between a fixture's resistance and a poor connection resistance, right?)
I mean, besides a smoke detector?
 
Every outlet in my apartment is loose - they don't have the strength or ability to hold a plug without them sliding out. The front desk lady said this was normal and the outlets in her apartment are the same way.
 
Let'sgoflying! said:
Excellent, Kent. Thank you. I too am all for non-purist explanations, so that works great.
Now I have to wonder though, getting all practical on you guys, I know - what devices could detect that unplanned resistive load, and disconnect the circuit stopping the fire? (the CB can't - it can only trip when...amp draw is excessive, correct? The CB cannot distinguish between a fixture's resistance and a poor connection resistance, right?)
I mean, besides a smoke detector?
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https://en.wikipedia.org/wiki/Arc-fault_circuit_interrupter is about as close as you can get. May or may not have tripped in the original case. And, these have been known to trip when you do bad things like turn on a TV with a perfectly functional switching power supply.
In some cases, a ground fault device may work.
The problem is that there is no way for a passive device to determine what load is planned or unplanned.
 
overdrive148 said:
Every outlet in my apartment is loose - they don't have the strength or ability to hold a plug without them sliding out. The front desk lady said this was normal and the outlets in her apartment are the same way.
Click to expand...
Time to move!
 
Let'sgoflying! said:
Excellent, Kent. Thank you. I too am all for non-purist explanations, so that works great.
Now I have to wonder though, getting all practical on you guys, I know - what devices could detect that unplanned resistive load, and disconnect the circuit stopping the fire? (the CB can't - it can only trip when...amp draw is excessive, correct? The CB cannot distinguish between a fixture's resistance and a poor connection resistance, right?)
I mean, besides a smoke detector?
Click to expand...

As mentioned, there are now arc-fault circuit interruptor outlets, and I think there are combined GFCI/AFCI outlets as well, but I don't think those would really help in this case.

In fact, the only good way to detect this would be to measure the voltage at the outlet end, which would see that voltage drop I talked about. However, the spec for voltage is pretty wide too, I think 10%, so your 120V could be 108V or 132V and still be (barely) within spec. In fact, my house tends to be near 130V. So, without measuring what is "normal" in your house (as measured at the panel), knowing the length of all the wire runs in your house, and measuring voltage at each of them... Well, it's kinda hard. Which is why this sort of thing is near-impossible to detect, and why houses still burn down.

Just remember, though, that once we stop burning houses down like this, they'll start burning books. ;) (If you don't get this - Go read Ray Bradbury's Fahrenheit 451. Or at least the wikipedia page on it.)
 
flyingcheesehead said:
As mentioned, there are now arc-fault circuit interruptor outlets, and I think there are combined GFCI/AFCI outlets as well, but I don't think those would really help in this case.

In fact, the only good way to detect this would be to measure the voltage at the outlet end, which would see that voltage drop I talked about. However, the spec for voltage is pretty wide too, I think 10%, so your 120V could be 108V or 132V and still be (barely) within spec. In fact, my house tends to be near 130V. So, without measuring what is "normal" in your house (as measured at the panel), knowing the length of all the wire runs in your house, and measuring voltage at each of them... Well, it's kinda hard. Which is why this sort of thing is near-impossible to detect, and why houses still burn down.

Just remember, though, that once we stop burning houses down like this, they'll start burning books. ;) (If you don't get this - Go read Ray Bradbury's Fahrenheit 451. Or at least the wikipedia page on it.)
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Also note that “normal” can change if the utility has to perform switching and changes your source location.
 
AFCIs are now mandated for all new work and renovations for residential properties in our county. Drawbacks and all.
 
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