How many Amps to burn up 14/2 electrical wiring?

We overload standard 14/2 wire commonly used in Canadian and American houses to find out how much current it can handle before it melts and burns up. Spoiler: It handles way more than its 15 Amp current rating as one would hope for a good safety margin. Of course it should never normally to subjected to anything beyond than its standard current rating.

[lonedesertfox]

Would be good to have a thermal imager rather than relying on touching the live wire (that is rigged to fail). This was a great video though, none the less!

[scottwillis]

Keep in mind this experiment has the Romex in open air, which is reasonably good for letting heat escape, instead of passing through insulation in a wall cavity. Also he's only giving it several seconds to heat up. Don't use "didn't catch fire after 10 seconds in free air" to decide what wire gauge you will use inside walls!
If the jacketed wires are warm on the outside of the jacket, they're hotter inside the jacket, and hotter still inside the wire insulation. And most of us hope our house wiring will last for decades.
6:50 watch the voltmeter climb: the resistance of copper wire increases with temperature. It's getting hotter.

[jdrissel]

Note the voltage drops at 8:22. That drop in voltage means the resistance decreased. In this setup, that can only mean that the wires are now touching before they get to the wirenut. In a voltage driven circuit (such as household power) at that point the current and power would have gone way up. Since I think we can assume that to get to that point the circuit protection has failed, at that point I would say the fire starts...

[danielhoughtelling]

The temperature rating of that 14AWG NMB cable is 90°C. The amp rating is good to 25A. The NEC prohibits its use over 15A. Nice demonstration.

[Asrok]

I worked in cable, when foreign voltage melted our lines, it was always at the splice points of the tap or the ground block. We could cut the melted part off and the cable would still be fine. You need to test a longer length circuit with multiple splice types for an accurate test.

[shadowdemon]

Try this with wire nuts and wego connectors and see which holds up best

[realmetallurgist]

A few years ago I was doing some welding, and absent-mindedly attached my grounding clamp to my bandsaw, and the return current found it's way through the 120 volt shop wiring. It lasted about 20 seconds at 75 amps before it let loose. Lots of charred insulation.

[allenblum]

I'm not surprised the wire nut didn't heat up appreciably. It really isn't carrying any current. Since the connection is actually the twisted wires, the wire nut serves only as an insulator.

[erikyoung]

Pretty Cool.. I'll never doubt wiring up a motor again with the yellows!

[carylamari]

As a 66 year old Master Electrician I appreciated your test. It helps to see the tolerances of the material we use in the field so we have a better foundation to talk to our customers. We all go through the classes and books but to actually see the breakdown of the conductor is impressive. This gives me more confidence in the load carrying capacity of house wiring especially with today's insulations which raise or lower the load capacity. Thanks ;)

[fredacuneo]

Great demonstration. Thank you. The wire can really take quite a bit of amperage before it failed.

[iczer]

I was gonna try to do this, but I didn't know how to do it safely. Should've known that someone else would have already done this. Thank you!

[kenkirton]

just an FYI
the adoption of twisting wires before putting on the connector came from the use of Marr connectors which had a small screw in the side which held the two wires together. if you didn't twist the wires then they became flattened as you tighten the screw and there is a lot of chance the cross-section area of The wire would become very reduced and over a period of time of heating and cooling the Matt connector would loosen off.
Ken

[LFTRnow]

This was interesting to see, and one should keep in mind this is in open-air. If you had a fan blowing on it, it would go higher, and if you put building insulation around it, it would heat up much faster and support less current. Finally, the fact it burned at the corner is also a clue, the thinner the wire is at a particular location, such as a bend or pinch-point, the greater the resistance there, and the more heat generated. So, to compensate for all of those factors and more, it is rated for 15A max to ensure safety.

[VB-bklh]

When I bought my home 10 years ago most of the house was wired with 10ga cloth and vinyl wrapped wiring, with some scattered modern 12/3 for new outlets added, and they added 10/3 to dedicated outlets to each window air conditioner outlet.
The worst overload was the living room which had four lamps, each with a 100w bulb and run off a single run of 12/2 w/o any ground, which also included the front porch lights and two outside outlets and four single bulb fixtures in the basement below, each with 100w bulbs.
It showed no sign of any failures but I did run new 12/3 runs to each outlet, one to the porch and two to the basement lights on that side when I tossed the old screw in fuses for a new breaker panel. The old wiring was plastic insulated wires in some sort of silver cloth wrap.
A few bulbs in the basement still have that wiring but little by little I'm replacing those fixtures with LED units, and for now, every bulb in the house is LED.

[jimturpin]

That was interesting AND educational! Well done! Never thought to test house wiring before, but I feel a lot better about the wiring in my house now.

[stephenbrickwood]

Do it again with home insulation around the wire.
Many people put their wiring buried in home insulation.
Good demonstration.

[jeffa]

I once ran a 1500(?)1800(?) watt space heater on a 100 ft 12 gauge extension cord that was wrapped around one of those plastic circular cord wrap things- so the cord was insulating itself from cooling off.
I was just going to run it for 20 minutes so I thought it would be OK.
I ended up falling asleep and when I awoke suddenly 5 hours or so later and ran out to the garage the whole garage smelled like hot plastic and the cord insulation was noticeably soft.
It permanently changed the insulation on the outside of the extension cord

[zephsmith]

The voltage suddenly dropped to nearly half at the point that the insulation began melting even as the copper heated and began increasing its resistance. Then it began rising again from the lower value.

I suspect a short part way along the cable, which reduced the impact further down the line (eg: at the far connector).

[mknow]

Thanks for this video. I now understand why our local code limits voltage drop on cables to 3%. In extra long cable the heating effect would be even greater and so the current capacity even less.