A scary discovery, what's going on?

[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/...act-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.

IMG_6857.jpg
IMG_6858.jpg

[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