A scary discovery, what's going on?

[roger wiegand]

I went out to my shop to turn the lights off just now; the programmable switch had lost its memory due to a prolonged power outage. To my surprise the switch box was blazing hot. The picture below is what I found inside. Needless to say this scared the wits out of me. I've powered off the circuit to think about what to do. I use the switch every day and have never noticed it being hot before.

In theory the circuit should not be overloaded. I have 12 two-bulb T5HO fluorescent fixtures for light in the shop. at 54 watts/bulb that should consume 12 X 2 X 54= 1296 watts. The 15A circuit should be able to support safely 80% of 15A or 0.8 X 1800 watts = 1440 watts continuous load. The overhead lights are the only load on that circuit.

In practice the wire nuts are melting!

Any insight as to what's happening here? Obviously I could split the lights onto two breakers, but that would be a pain and they really should be safe as-is.

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[Cameron Wood]

Looks like a bad wire connection overheating- very apropos of the arc fault discussion.

[Lee Schierer]

I would be interested whether the wires are twisted together or just bunched together and held by the wire nut.

[Tom M King]

I was getting ready to ask the same question that Lee asked.

[Dave Zellers]

I would be interested whether the wires are twisted together or just bunched together and held by the wire nut.

Exactly what I was wondering. Are the wires loose and arcing?

[Bill Dufour]

I think Wagos are harder to mess up then wire nuts but they take up more room. When you redo those connections you will have to clean and expose the wire to bright copper. Soot is an insulator. I assume no aluminum was involved?
Bill D

[roger wiegand]

I will take a picture and post it when I take it apart later this morning. No aluminum. This was wired about a decade ago. They are almost certainly twisted, as that's how I was taught to do it.

Is twisting a good thing or a bad thing? The interweb seems to be divided pretty close to 50-50 on the subject. Some manufacturers say it's not necessary, but don't say not to do it.

[Jim Becker]

Pre-twisting provides a very positive connection, IMHO. I've also now moved to Wago connectors, but if I do a wire nut, I always pre-twist with lineman's pliers, clean/trim the end and then apply the wire nut followed by tape.

It will be interesting to see what you find when you peel that apart to see why it's arcing.

[Edward Weber]

Pre-twisting provides a very positive connection, IMHO. I've also now moved to Wago connectors, but if I do a wire nut, I always pre-twist with lineman's pliers, clean/trim the end and then apply the wire nut followed by tape.

It will be interesting to see what you find when you peel that apart to see why it's arcing.

I haven't used the Wago but that's the way I've been doing wire nuts for decades.

[Jim Becker]

I haven't used the Wago but that's the way I've been doing wire nuts for decades.
I "discovered" them when I was wiring the new shop, Edward. They were a game changer, especially with the heavy #10 wire on the machine circuits. They also need to be taped, IMHO, but there's a lot less screwing around with tools...cut, strip, insert and lock, tape. Done.

[roger wiegand]

It's going to be embarrassing in all likelihood, but here are my best guesses. I believe strongly in the importance of "near miss" reports for improving safety. I've sure had an important lesson.

The stranded wire from the timer switch is the principal point of failure. I see several things when inspecting the wire and the connection.
1) The stranded wire is melted along its length
2) it appears to be wrapped around the solid wire several times and in good contact with both the solid wire and the spring inside the wire nut.
3) It appears corroded inside the wire nut
4) it looks as though several strands (3-5) of the stranded wire were broken off short and possibly not in contact with the solid wire (poor wire stripping technique?)
5) the other two connections appear similar, but are uncorroded and not melted

Possible issues:

1) missing strands will clearly lower the ampacity of the wire, resulting in greater heat; why this only became apparent after a decade is unknown.
2) the wire nut was one of the lightweight ones that come for "free" with the switch, the others were of much higher quality. A possible source of corrosion? (Circuit was (unusually) out of use for 10 days with very high humidity, a contributing factor?)
3) stranded wire was not tinned

Suggested solutions:

1) Greater care in handling stranded wire
2) tin the ends of the stranded wire
3) Employ a clamp-type connector to join stranded to solid wire
4) Check all other similar installations in the house and shop, correcting as needed

My tentative conclusion is operator error on installation, and possibly a low quality wire nut.


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[Bert McMahan]

I'm no electrician but I don't think you want tinned wire in a compression connection. I've personally seen two equipment failures (one very expensive) due to a tinned, stranded wire being installed in a screw terminal (i.e., compressed under a screw head). The solder will creep over time and cause the joint to fail. I don't know if this applies to a wire nut also, but since it's a compression fitting as well I would err on the side of not tinning stranded wire.

No idea why your wire melted though!

[roger wiegand]

Oh, something else to learn about. My friend, who is an electrical engineer and an old-time TV/radio repair guy, has been telling me to always tin the ends of stranded wire.



I'm no electrician but I don't think you want tinned wire in a compression connection. I've personally seen two equipment failures (one very expensive) due to a tinned, stranded wire being installed in a screw terminal (i.e., compressed under a screw head). The solder will creep over time and cause the joint to fail. I don't know if this applies to a wire nut also, but since it's a compression fitting as well I would err on the side of not tinning stranded wire.

No idea why your wire melted though!

[Bert McMahan]

Do you mean for wire nuts or for other uses? You definitely don't want to tin wires for crimp connections, and AFAIK you don't want to tin wires in screw terminals (as I mentioned, I've seen them come loose myself). You can probably do it for very small/fine wires to keep them together, but not for the really thick stuff.

Plus, if the connection heats up and the solder softens then your connection will get even worse.

You absolutely should tin wires before soldering them, but I don't think you want solder in any "physical" connections (like a crimp, ferrule, or screw terminal). I do think there are some ferrules designed to be crimped on THEN filled with solder, but not the other way around.

[John Lanciani]

In theory the circuit should not be overloaded. I have 12 two-bulb T5HO fluorescent fixtures for light in the shop. at 54 watts/bulb that should consume 12 X 2 X 54= 1296 watts. The 15A circuit should be able to support safely 80% of 15A or 0.8 X 1800 watts = 1440 watts continuous load. The overhead lights are the only load on that circuit.


I suspect your circuit current is a fair bit higher than you think. You haven't accounted for the power consumed by the ballasts, nor have you accounted for the power factor of it. (Watts are never equal to volts x amps in the real world, you must know the power factor to calculate watts) I'd bet an internet buck or two that your circuit current is +/-14 amps.

[Rollie Meyers]

You have to account for the ballast loss in addition to the lamps.

[roger wiegand]

OK, yes, I forgot about that. Unfortunately I don't have any way to measure the actual amperage.

[Michael Burnside]

There is no way that timer switch is rated for 15A continuous current or even 80%. I don't know if the specs are written on it or not, but even if it were 3-7 stranded cores you'd be looking at TOPS 10A and most likely 7 or 8 looking at the pictures and assuming > 10 cores. Maybe it would spec 10-12A, but given the lights you have and assuming +/- variability, current the timer draws itself, temperature, etc., no way it can handle the load safely.

[Dan Friedrichs]

There is no way that timer switch is rated for 15A continuous current or even 80%. I don't know if the specs are written on it or not, but even if it were 3-7 stranded cores you'd be looking at TOPS 10A and most likely 7 or 8 looking at the pictures and assuming > 10 cores. Maybe it would spec 10-12A, but given the lights you have and assuming +/- variability, current the timer draws itself, temperature, etc., no way it can handle the load safely.

Looks like it's Honeywell rpls740b, and the manual for it does say 15A @ 120V...

[Dan Friedrichs]

1) The stranded wire is melted along its length

It's hard to tell from the pictures, but it sure looks like the stranded wire insulation is melted all along the length (from the nut to the switch), but that is the "line" wire, and the output ("load") wire from the timer looks to be in fine condition. If it were an overcurrent condition, you'd expect both of those to heat equally. So it seems safe to assume it's not related to excessive load (or the load wire would be melted, too).

The wire nut may be suspect, but it sure looks like it's well-twisted. The risk, here, is that poor contact between the wires causes high resistance and heating. This would affect both the solid (input) wire and stranded (output) wire - are both exhibiting melting? (Understandably, the solid wire may be less heated due to larger gauge or higher thermal mass). But I'm suspicious of this, too, because SO MUCH of the stranded wire insulation is melted - it seems to have melted all the way along the length, including a long distance from the wire nut. The "wire nut failure mode" is that heat is generated at the connection point within the nut - the stranded wire being melted so far back seems to not support this theory.

Is it possible there was a short between the stranded wire and another wire in the box? If the stranded wire had a nick in the insulation and was touching one of those bare ground wires, that could cause high current just in that segment of stranded wire and explain all of this.

You mention loss of a strand or two being a concern, but I don't think that's the case. Loss of a few strands would cause a local area of higher-resistance, but once those strands join the larger bundle, current will flow out into all strands.

From these pics, I really think there was some alternate path for current to flow through that stranded wire...

[roger wiegand]

The spec is 15A; 1800 watts or a 3/4 hp motor according to the manufacturer. It's a UL listed device, and I hope a company like Honeywell doesn't fudge the numbers. I talked with a pretty knowledgeable tech support person at Honeywell this afternoon. They couldn't pinpoint a problem, suggesting several of the same options as came up here and also suggested the possibility of a voltage surge from lightning. They recommended confirming the load and either splitting it or upgrading the wiring and switch to something heavier duty if it's close. Rewiring with 12 ga would be a lot harder than making it work on two independent circuits. They confirmed that it should be fine if my initial wattage calculation were correct.

I've just ordered myself an ammeter after needing one multiple times over the years and can actually see what the current load is. I'm now guessing it's going to be high. I'm thinking I'll probably have to split the lights onto two different circuits with two switches. LED conversion is another alternative, but the replacement bulbs I've found so far are only 60% as bright and still use half the wattage so I might end up having to buy and install more fixtures, something I'm loathe to do.


There is no way that timer switch is rated for 15A continuous current or even 80%. I don't know if the specs are written on it or not, but even if it were 3-7 stranded cores you'd be looking at TOPS 10A and most likely 7 or 8 looking at the pictures and assuming > 10 cores. Maybe it would spec 10-12A, but given the lights you have and assuming +/- variability, current the timer draws itself, temperature, etc., no way it can handle the load safely.

[roger wiegand]

Interesting thought. I too was surprised at the difference between the line and load wires from the switch. The load wire (the blue one) was perfect, no sign of overheating at all. I would have thought they should carry the same current. I saw nothing in the box that suggested a short opportunity, but the black wire was pretty well destroyed. The box was not crowded, because the switch is physically large I used a double box for the single switch. The ground wires were folded all the way to the back of the box, not close to the line wire that melted.


It's hard to tell from the pictures, but it sure looks like the stranded wire insulation is melted all along the length (from the nut to the switch), but that is the "line" wire, and the output ("load") wire from the timer looks to be in fine condition. If it were an overcurrent condition, you'd expect both of those to heat equally. So it seems safe to assume it's not related to excessive load (or the load wire would be melted, too).

The wire nut may be suspect, but it sure looks like it's well-twisted. The risk, here, is that poor contact between the wires causes high resistance and heating. This would affect both the solid (input) wire and stranded (output) wire - are both exhibiting melting? (Understandably, the solid wire may be less heated due to larger gauge or higher thermal mass). But I'm suspicious of this, too, because SO MUCH of the stranded wire insulation is melted - it seems to have melted all the way along the length, including a long distance from the wire nut. The "wire nut failure mode" is that heat is generated at the connection point within the nut - the stranded wire being melted so far back seems to not support this theory.

Is it possible there was a short between the stranded wire and another wire in the box? If the stranded wire had a nick in the insulation and was touching one of those bare ground wires, that could cause high current just in that segment of stranded wire and explain all of this.

You mention loss of a strand or two being a concern, but I don't think that's the case. Loss of a few strands would cause a local area of higher-resistance, but once those strands join the larger bundle, current will flow out into all strands.

From these pics, I really think there was some alternate path for current to flow through that stranded wire...

[Dan Friedrichs]

That switch, itself, just contains a relay that opens and closes on command. Ideally, it generates no heat, itself, so 15A or 20A or even 25A should have a trivial impact on it. It's not like an old rheostat or something that is going to get hot. So: I really doubt this has anything at all to do with overloading the circuit (presuming the circuit is even overloaded, which it may not be).

Bizarre, scary situation, for sure.

[Mike Soaper]

I'm wondering about the corrosion , ie. was there an earlier event that cooked the insulation and exposed the wire so it corroded , or was the corrosion on the wire inside of the insulation. Either way maybe the corrosion caused enough of copper loss, or broken conductors reduce the wire's current capacity.

Maybe strip a section of the insulated part of the corroded wire near the device to see if it's corroded inside of the insulation

[Karl Loeblein]

I replace my fluorescent lights with lower wattage LEDs. Much brighter and no delays starting up in the cold winter. My only regrets is not doing it sooner.

[roger wiegand]

I replace my fluorescent lights with lower wattage LEDs. Much brighter and no delays starting up in the cold winter. My only regrets is not doing it sooner.

I'd like to find such a thing, The T5HO bulbs are 5000 lumens each, the brightest LED replacement I've found for them is 3500. Lumens/watt is quite close between the two-- the t5HO bulbs are quite efficient. The available replacement bulbs I've found also have an even worse CRI, not great for finishing.

[Karl Loeblein]

Roger, I found it cheaper to replace the entire fluorescent fixture and it looks better too. You also get a lot more lumen and CRI options with replacement fixtures.

This is much brighter in person, but my iPad auto darkened the pic because to light was too bright for the camera.

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[Alan Lightstone]

Pre-twisting provides a very positive connection, IMHO. I've also now moved to Wago connectors, but if I do a wire nut, I always pre-twist with lineman's pliers, clean/trim the end and then apply the wire nut followed by tape.

It will be interesting to see what you find when you peel that apart to see why it's arcing.
I use similar connections for all my low voltage cabling connections. Didn't know about the Wagos. Do they take up more room in an outlet box? How do you size them for two different size wires in same connection (like hooking up the timer)?

[Jim Becker]

I use similar connections for all my low voltage cabling connections. Didn't know about the Wagos. Do they take up more room in an outlet box? How do you size them for two different size wires in same connection (like hooking up the timer)?
While I have the 10 gage version which will not work on smaller gage wire, the smaller sized version works for both 14 and 12 gage, I believe. There are some similar products at the home center (not Wago brand) that are 14/12, I believe) S

So if you need to join smaller wire to #10 for some reason, I suspect you'll still need to use the wire nuts. But that should not be a common scenario I would think...

[Michael Burnside]

Looks like it's Honeywell rpls740b, and the manual for it does say 15A @ 120V...

I wouldn't trust it to handle 15A continuous with the number of strands. If the circuit breaker is 15A and isn't tripping, then it's clear the weak point is the timer. A current meter would be a good thing to have in this scenario. My recommendation would be to replace the lighting with LED anyway.

[George Yetka]

Pre-twisting provides a very positive connection, IMHO. I've also now moved to Wago connectors, but if I do a wire nut, I always pre-twist with lineman's pliers, clean/trim the end and then apply the wire nut followed by tape.

It will be interesting to see what you find when you peel that apart to see why it's arcing.


Ive been told by Electricians(more than 1) on the job that wagos are no good, they eventually come loose. I have not witnessed this and do use them myself. It may be a pipefitter doesnt like propress because it takes my work situation though.

[Wayne Cannon]

The insulation material on the stranded material may have a lower melting point in addition to less thermal mass. Just a thought.

[Jim Becker]

Ive been told by Electricians(more than 1) on the job that wagos are no good, they eventually come loose. I have not witnessed this and do use them myself. It may be a pipefitter doesnt like propress because it takes my work situation though.
I don't see them coming loose with the tape wrapped around them, but un-taped, the little tabs could release when one is pushing them around in the box. Most of those I've used are in "yuge" boxes which feed out to machine locations, so it's not a tight space. I'm not personally worried about them. A number of electricians around here use them and when I asked the electrician who installed my service, he offered no cautions.

[roger wiegand]

Given the number of failures of joints made with wire nuts I've seen personally over a couple decades of home renovations the Wago's would have to be pretty terrible to be worse. They seem less subject to user error in installation (I just received my first box of lever lock Wagos, haven't used any yet). There's a phenomenon with almost every new technology where someone's uncle's brother in law heard of a failure of the new product and now everyone thinks it's junk. The introduction of PEX would be a good example, or the utter nonsense that circulates about electric cars. Of course the stories of polybutylene and cPVC water pipes might be a good counterexample. The lever connectors have been used since 2003, if they failed at an unusual frequency I think the NFPA/code folks would have noticed by now.

[Ken Fitzgerald]

A few weeks ago, I lost a ballast in one of the 15, 4 bulb T-8 lights in my shop. When I replaced the ballast, I discovered the Wago connects. In my 40+ years servicing everything from radars used in air traffic control to CT and MR scanners, I used a lot of twist on connects. I like the Wago connectors!

[Michael Burnside]

Ive been told by Electricians(more than 1) on the job that wagos are no good, they eventually come loose. I have not witnessed this and do use them myself. It may be a pipefitter doesnt like propress because it takes my work situation though.

My friend is an electrician and uses them all the time. He says they are great for tight places and are code approved. We used them in my shop for the 240V because they are a lot cleaner when wiring 10 or 8 gauge wire. They're not coming lose any more than a properly installed wire-nut with the ends pre-twisted beforehand.

[Cameron Wood]

I'm no electrician but I don't think you want tinned wire in a compression connection. I've personally seen two equipment failures (one very expensive) due to a tinned, stranded wire being installed in a screw terminal (i.e., compressed under a screw head). The solder will creep over time and cause the joint to fail. I don't know if this applies to a wire nut also, but since it's a compression fitting as well I would err on the side of not tinning stranded wire.

No idea why your wire melted though!



I disagree with this- stranded wire wrapped under a screw head is a mess and tinned is better. Likewise tinned stranded wire is better in a wire nut or in a crimped connector (but matters less there).

I've used Wagos and have somewhat mixed opinion. Good for switch boxes (they take up less room, not more), and fine for connecting a light fixture, but they are basically the same mechanism as push in connections on the back of household switches and receptacles, which while approved, are the cause of many electrical problems and something that I never use.

(I am an electrician- well, general contractor with 45+ years in electrical)


The missing strands that were cut in stripping is not a factor, IMO. Wire connections in switch boxes often get compromised from pushing the wires back into the box, especially if they were not planned to go in without stress. I never tape wire nut connections- just makes a sticky mess and doesn't add anything. Never see it in professional installations. Since your load is up there & there's been a problem, it would be good to check the current draw- lots of clamp on units around for borrow or buy.

[Dan Friedrichs]

Since your load is up there & there's been a problem, it would be good to check the current draw- lots of clamp on units around for borrow or buy.

If that were the root cause, why was the wire out the other side of the switch not affected?

[Cameron Wood]

If that were the root cause, why was the wire out the other side of the switch not affected?


Probably because the wire nut connection was better. I don't think the high draw is the root cause, but could be contributing. If the load was less, maybe the wire would not have overheated, in spite of a poor connection.

[Jim Becker]

I've used Wagos and have somewhat mixed opinion. Good for switch boxes (they take up less room, not more), and fine for connecting a light fixture, but they are basically the same mechanism as push in connections on the back of household switches and receptacles, which while approved, are the cause of many electrical problems and something that I never use.

While I agree with never using push-in connections on switches and outlets, Wagos are not quite the same. While you "can" use them as push in, if you flip the lever, you can easily insert the bare wire end and then put the clamp in place positively so it bites as it's supposed to do. The wire remains nearly pristine. You do have the advantage of disengaging a wire if you need to by flipping the lever to release it. Of course, that's also why I recommend taping them, too.

[Cameron Wood]

While I agree with never using push-in connections on switches and outlets, Wagos are not quite the same. While you "can" use them as push in, if you flip the lever, you can easily insert the bare wire end and then put the clamp in place positively so it bites as it's supposed to do. The wire remains nearly pristine. You do have the advantage of disengaging a wire if you need to by flipping the lever to release it. Of course, that's also why I recommend taping them, too.



Actually, the ones that I have mainly used are another brand, & don't have the lever- similar to what comes preinstalled on recessed light cans these days.

[Ron Selzer]

Roger, I believe the device failed internally increasing the resistance resulting in high amperage needed to provide required amperage out to lights. I base this on a situation back in the 1990's on a Chiller feed with 4/0 wire to a circuit breaker, factory provided on the Chiller. The insulation melted back on the wire feeding the circuit breaker, one of three, the wire leaving the circuit breaker was never damaged. I had installed 3 split core current switches per control drawings. Once the chiller ran for less than a day, I had to use a hammer to break the melted plastic cases to remove the current switches. Only after the circuit breaker was changed out did the wire remain undamaged. there was a measurable voltage drop thru the circuit breaker when the chiller was operating.

[roger wiegand]

Another interesting idea. The switch is still working fine, I can measure the resistance.


Roger, I believe the device failed internally increasing the resistance resulting in high amperage needed to provide required amperage out to lights. I base this on a situation back in the 1990's on a Chiller feed with 4/0 wire to a circuit breaker, factory provided on the Chiller. The insulation melted back on the wire feeding the circuit breaker, one of three, the wire leaving the circuit breaker was never damaged. I had installed 3 split core current switches per control drawings. Once the chiller ran for less than a day, I had to use a hammer to break the melted plastic cases to remove the current switches. Only after the circuit breaker was changed out did the wire remain undamaged. there was a measurable voltage drop thru the circuit breaker when the chiller was operating.

[Lee Schierer]

To me it looks like the failure was a really cheap and undersized wire nut. Note that the wire nut that failed is smaller than the others in the box. Most likely it was the wire nut supplied with the switch intended for connecting the switch to a single wire, not gripping the three wires of the connection.504137 504138

[Ron Selzer]

Another interesting idea. The switch is still working fine, I can measure the resistance.

Should not be able to measure any resistance thru the switch as this will indicate a voltage drop condition and amps being used to generate heat.

[Jim Becker]

Actually, the ones that I have mainly used are another brand, & don't have the lever- similar to what comes preinstalled on recessed light cans these days.
Try a "real" Wago sometime...they are a pleasure to use.

[Dan Friedrichs]

Should not be able to measure any resistance thru the switch as this will indicate a voltage drop condition and amps being used to generate heat.

If the switch had some measurable resistance, then the whole circuit would draw less current, not more. And the switch itself would have been heating. Does not explain why the wire insulation melted.

[Bert McMahan]

Couple things, first, you can't measure the resistance of a normal relay/switch with a regular multimeter (you need a 4-wire measurement to do that), BUT you WILL see a measurement if you try. It'll be a couple ohms or so, basically the resistance of the leads of the meter plus the contact resistance of what you're touching, plus any noise at the low end of the measurement device capability. It won't be an accurate measurement.

Second, if you DO measure some increased resistance, then it would be indicative of some kind of failure. The whole circuit may draw less overall current, but the current/power sinking across that resistance will go way higher so you could get localized heating.

Ballpark math: assume everything is resistive (since we're dealing with heat). Normally the resistance of a relay is in the neighborhood of 100 mOhms (https://na.industrial.panasonic.com/blog/how-measure-relay-contact-resistance). Power is I^2 * R, so for 15 amps you have 15 * 15 * 0.1 = 22.5 W.

Pretending again that the load is resistive, 120 V / 15 A = 8 ohms (for the lighting).

If some lightning or corrosion or whatever increased the contact resistance to, say, 2 ohms, then the total system draw would then be 120 V / 10 ohms = 12 A, which is a lower total power. However, the contact resistance now sees 12 * 12 * 2 = 288 W.

Thus, despite the total load going down, the individual component heat load goes WAY up. Still, like Dan said, that affects the component, not the system, so no idea why the wire would melt along its whole length unless it was just touching the component.

That doesn't explain exactly why the wire melted along its length, but it could be the heat from the resistor traveling along one of the wires. It would be interesting to see the inside of the switch to see if there is internal burning as well.

[Curt Harms]

While I agree with never using push-in connections on switches and outlets, Wagos are not quite the same. While you "can" use them as push in, if you flip the lever, you can easily insert the bare wire end and then put the clamp in place positively so it bites as it's supposed to do. The wire remains nearly pristine. You do have the advantage of disengaging a wire if you need to by flipping the lever to release it. Of course, that's also why I recommend taping them, too.

I think there are 2 styles of 'push in' connectors. The problematic one just uses a single springy strip of metal and the connection is questionable. There is a style that uses a screw clamp. Strip the wire, stick it in the back and tighten a screw. Those are fine AFAIK and don't require wrapping around screws. I find 12 ga. wire a challenge to wrap around a screw securely, wouldn't even want to think about 10 ga.

[Jim Becker]

I think there are 2 styles of 'push in' connectors. The problematic one just uses a single springy strip of metal and the connection is questionable. There is a style that uses a screw clamp. Strip the wire, stick it in the back and tighten a screw. Those are fine AFAIK and don't require wrapping around screws. I find 12 ga. wire a challenge to wrap around a screw securely, wouldn't even want to think about 10 ga.
The screw clamp type is called "backwire" and is very secure clamping of the wire. it's all I use.

[roger wiegand]

My ammeter finally came in. Actual load on the circuit is 13.2 A. So it is overloaded, but not outrageously so. Adding an extra lamp over a dark spot a couple years ago pushed me over the edge. With an ordinary toggle switch in place the wire gets barely warm. Splitting the lights onto two circuits will certainly alleviate any issue. I'm also looking into installing a monitored fire alarm.

Here's what the inside of the switch looked like. To my eye the overheating seems completely confined to the black "line" wire. Nothing inside the switch looks singed.

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[Tom Bender]

So if only the line lead melted it may have been carrying more amps than the load side. The difference would have to be consumed inside the switch, sending those extra electrons back thru the ground wire. Time to trash the switch.

[roger wiegand]

At this point Im only keeping it as a prompt to get off the dime and get a monitored fire alarm installed in the building!


So if only the line lead melted it may have been carrying more amps than the load side. The difference would have to be consumed inside the switch, sending those extra electrons back thru the ground wire. Time to trash the switch.

[Lee Schierer]

I still think the problem started with a poor connection caused by the undersized orange wire nut.

[roger wiegand]

I still think the problem started with a poor connection caused by the undersized orange wire nut.

That is also my suspicion. The orange nut was certainly not undersized in Honeywell's estimation-- the new switches I got come with the exact same nuts-- however I'm going to follow my now usual practice of pitching the nuts that come with a switch. They are much smaller and lighter than the nuts from the electrical supply place rated for that number of wires. I've acquired a box of the lever-lock Wagos, they look like a better choice for joining stranded to solid wire. I'm also splitting the lights onto two circuits to avoid the over-current situation. And installing a monitored fire alarm.

[Christopher Charles]

Glad to hear you've been able to isolate the issue and thanks for sharing!

[Tom M King]

Sounds like you've found a safe solution. I'm glad the only thing burned up was a short piece of wire. I expect we all learned something in the process too.

[Jeff Bartley]

Glad this wasn’t worse Roger! Tell us about the monitored fire alarm once you have it in place, I’m not familiar with those.

[Lee Schierer]

That is also my suspicion. The orange nut was certainly not undersized in Honeywell's estimation-- the new switches I got come with the exact same nuts-- however I'm going to follow my now usual practice of pitching the nuts that come with a switch. They are much smaller and lighter than the nuts from the electrical supply place rated for that number of wires. I've acquired a box of the lever-lock Wagos, they look like a better choice for joining stranded to solid wire. I'm also splitting the lights onto two circuits to avoid the over-current situation. And installing a monitored fire alarm.

I suspect that Honeywell expected the switch to be connected to a single wire not the two wires that are in your wiring setup. You often see the same wire nuts in new light fixtures and they don't work well on #12 wire. I guess the manufacturers expect lighting circuits to be 14 gauge. The OEM provided wire nuts go in the trash. I use better quality ones.

[Bill Dufour]

I doubt a meter will tell you much about the switch. It probably has a transformer or a circuit to reduce voltage for control voltages. Unless your meter puts 120 volts ac into the switch it is not really doing anything.

Kind of like using a meter to check a contactor and wondering why the 120 volt acc coil does not move at 1.5 volts dc.
Bill D