Why my thermostat wires are burnt (Honeywell 5000w with 5000w heater)

ostie01 · Feb 25, 2018

This is a 5000W Honeywell thermostat and last night, a smell of burned plastic grabbed my attention, looked at the thermostat and saw these burned wires, what happened? Heater is 5000w too

Jeff

Residential Thermostat - 12/24V - 5W | RONA

Billtodd · Feb 25, 2018

crappy twist joints !

ostie01 · Feb 25, 2018

Billtodd said:
crappy twist joints !

What you see in the picture is the cooper part that is inside the wire nut, the plastic part melt, and fall.

steve-l · Feb 25, 2018

This is an example of what not to do. Billtodd is exactly correct. Twist nuts like these should never be used for electrical connections. Resistive connections cause a voltage drop across the connection, which results in heat and more corrosion and more resistance and more heat etc etc in a snowball effect.

ostie01 · Feb 25, 2018

steve-l said:
This is an example of what not to do. Billtodd is exactly correct. Twist nuts like these should never be used for electrical connections. Resistive connections cause a voltage drop across the connection, which results in heat and more corrosion and more resistance and more heat etc etc in a snowball effect.

So what should be done?

steve-l · Feb 25, 2018

ostie01 said:
So what should be done?

Cut out the overheated wire. Strip back the insulation the correct amount for an appropriate crimp connector. Thoroughly clean the bare wire ends of any coating or corrosion to bright copper and crimp the wire ends together tightly, insulating the resulting connection with heat shrink tubing. If this is beyond your expertise, get an electrician to do it. Poor joints are a fire hazard.

SND · Feb 25, 2018

I've never seen an electrician in Canada use anything other than marrettes for that sort of thing in residential wiring, failures are really, really rare if done right. With said, call one to sort that out if you're not familiar enough with electrical stuff.

Hard to tell from the pic, but was that ground wire(from top of box) shorting on the red burnt one? I wonder if they made contact and then fried up without tripping the breaker somehow.
Otherwise, a bad connection/wiring that really overheated/shorted.
What size wire is that? At least #10? anything smaller is no go for that load.
When fixing that properly, you guys should also do a proper voltage and amp load check, make sure the heater is working as it should, could be other problems perhaps.

karl · Feb 25, 2018

Isn't there supposed to be an insulated bushing between the wires and the inside of the outer sheathing?
Karl

DDoug · Feb 25, 2018

ostie01 said:
What you see in the picture is the cooper part that is inside the wire nut, the plastic part melt, and fall.

Please READ & UNDERSTAND the knowledge given to you, by the
postings.

Stop putting up walls to the answers.

ostie01 · Feb 25, 2018

digger doug said:
Please READ & UNDERSTAND the knowledge given to you, by the
postings.

Stop putting up walls to the answers.

I'm so sorry, I offended her Majesty,
You know, we have anti-virus, anti-malware, anti-spyware, we are so ready for an anti know it all :nutter:

By the way, everything was by the code

And thanks for everybody esle.

Jeff

rons · Feb 25, 2018

What I do not like about those particular twist connectors are that over time the spring inside will corrode and rust and pit. But better than black tape.

SND · Feb 25, 2018

Yes, anti-short bushings are supposed to be used, but many don't, though that didn't cause this issue.
Personally I'd use a bigger box while fixing this since its exposed anyway, that thing is cramped in there.
Check that your breaker is working properly.

gustafson · Feb 25, 2018

5000 watt is over 20 amps at 240, what gauge are those wires

gustafson · Feb 25, 2018

Also wire nuts are the standard way electricians do things, but they work poorly when mixing solid and stranded wire

rons · Feb 25, 2018

Looking at the pictures again, appears that the wire spring is still holding the wires. But the plastic housing evaporated away. Have never seen that before.

Leave box open and monitor temperature if you do the same thing again. The relation V = IR is what's going on there. Too much current across a resistance produces excess heat.

thermite · Feb 25, 2018

ostie01 said:
So what should be done?

I once liked a full twist, soldered. Or "split bolt" clamps. Crimps suck easily as badly as wire noughts, if not far worse.

Solid-conductor copper, I actually USE oversized wire nuts atop a really good "rat tail" or "pigtail" solid twist. Basically, the wire nut is but a rugged twist-on insulator by that point. That is all they were MEANT to be, after all.

The twist does the hard stuff. Always has done. Make it up with lineman's-pattern pliers before you even reach for a wire nut. Don't f**k up the pre-positioning or twist tightness and break a wire or leave one loose. Copper must distort, but not break, nor be stressed to where it WILL break, later. Tape, sleeve, wire nut or BOTH over. On to the next.

Practice on scraps of cut-off. Stress those. Bad technique shows itself. Good comes soon after.

A "Western Union splice" will even stand as much strain in tension as the wire itself. Any breakage or overheat will be elsewhere.

Not needed in a space heater, though. Not unless you are hanging the sumbich off the feed wire or it is maybe a trip-hazard?

Don't ASK why I can still DO a Western-Union splice, now. Ain't admittin' to nuthin'!

Tony Quiring · Feb 25, 2018

Wire nuts are in millions of places and work just fine.

When properly used.

The heat was there so something wrong.

The "duh" things need to be looked at.

Wire size correct for load as well as correct nut and application.

Never pre-twist the wires.

Both need to be equal length and clean as well as correct exposed length.

Imagine the meeting surface area needs to exceed the cross area of the conductors.

The nut will compress and twist as needed, pre-twisting may reduce the effect but the journeyman level electricians are better to explain that.

A clamp amp meter can confirm actual current flow to confirm if heater is functioning per labeled rate and the wire size should be checked as the wire may be rated for say 20 amps but something tells me that the wire size charts are for non - continuous loading at that rate and must be up - sized for continuous loads such as resistive heating but that again better asked of the licensed pros.

Sent from my SAMSUNG-SGH-I337Z using Tapatalk

gbent · Feb 25, 2018

ostie01 said:
I'm so sorry, I offended her Majesty,
You know, we have anti-virus, anti-malware, anti-spyware, we are so ready for an anti know it all

By the way, everything was by the code

And thanks for everybody esle.

Jeff

I don't know what code you used, but it certainly isn't to NEC here in the USA.

You told us how much power, but what voltage?

Use a larger box and split bolts when you redo your connections.

thermite · Feb 25, 2018

ostie01 said:
I'm so sorry, I offended her Majesty,
You know, we have anti-virus, anti-malware, anti-spyware, we are so ready for an anti know it all

By the way, everything was by the code

And thanks for everybody esle.

Jeff

If you listen to enough "know it alls" and learn to sort apparent contradictions, you may yet succeed.

No-nothings you can go out the house, stop the first passerby, roll the dice.

Inclement weather?

Just ask your own "Majesty" next time you are atop that porcelain "throne" in the shitter.

And we wonder why we have housefires?

"Code" didn't cause your problem.

"Code" just bit you right square in the ass to demonstrate you had NOT met the most relevant bits of it at a common as housefly poop, but nonetheless critical point!

WizardOfBoz · Feb 25, 2018

Ostie, I've always used wire nuts for most stuff, but the points made by others above, and your recent incident, suggest a more robust approach. You might use a "bug", that is a split-bolt connector. Your wires look like they're copper, but if one of them is aluminum, No-Alox claims that there antioxidant paste works with split bolts. Make up the joint per instructions, with No-Alox if appropriate. Cover with splicing tape (3M 130C linerless is probably easiest) and finish with electrical tape (such as 3M Super 33+).

Why my thermostat wires are burnt (Honeywell 5000w with 5000w heater)

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