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Here is a picture of the damage. Thank goodness they're was no fire. We had our breaker panel replaced today. I don't know if that's related or just coincidence.

Tonight about 8:30pm while getting showered for bed I noticed we had no hot water. The electrician had forgotten to hook up a different circuit in the house, so I thought maybe they forgot the water heater too.

Upon inspection the heater is now leaking, and I know it wasn't 2 days ago. The heater is very old, so I'm not surprised it's leaking.

  • My main question is what should I look for to determine the cause of the wire glowing red and the insulation burned off?
    • The fiberglass insulation behind the electrical cover was damp from a leak somewhere, but not soaking wet.
    • Could the water have made it conductive?
  • Could it be related to the panel?
  • Why didn't the breaker trip before it got that hot? It's a 30 amp 220v breaker (just installed today).

I'm having the electrician come back tomorrow, but I'd really appreciate any help or advice.

I found this situation. Why did a failing water heater emit an electrical burning odor?

Could it be the same issue?

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    Can you measure the diameter of that black wire? It looks like it is thick enough for a 30A current, though.
    – PMF
    Feb 6 at 8:06
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    Uh, just checking, but did you shut off the breaker after you took the picture? Don't leave it glowing like that!! Feb 6 at 17:09
  • Note that the thermostat is showing heat damage in its middle. I suspect that the heating element failed to short-circuit. The black wire's connection was the weakest link
    – CSM
    Feb 6 at 19:04
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    I wouldn't be surprised if the wire hadn't been bent several times at that position and developed a crack/thin spot, or perhaps been damaged by pliers in forming a loop or straight portion for connecting to the appliance. In short, if there is a little bit of damage right there that happened to make the wire thinner, that's where its resistance would be greatest and heating correspondingly high. Feb 6 at 20:55
  • 2
    Good points! I did turn off the breaker right after I took that picture.
    – JBurt
    Feb 7 at 5:53

2 Answers 2

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Joints get hot when they are not crimped or secured tightly. As they are loose this increases the resistance and this increases the losses which manifest as heat.

We often use the heating effect of an electric current but poor joints lead to damage as shown in your picture. Often the wire can break and that limits the damage but if the wire does not break then the heating continues which damages the surrounding parts.

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    Additionally, the heavy use of the wire causes thermal expansion, and when power goes off, the wire contracts again. In some treminals (like screw terminals), the can cause wear which decreases the contact patch size over time (like a few decades). The smaller contact patch has a higher resistance and in turn generates more heat, aggarvating the issue. So even wehen the connection was tight and secure 30 years ago, it might have evolved into situation described by Solar Mike. Water heaters, dishwashers, heaters, laundromates, EV chargers are typical candidates for occasional high current.
    – Klaws
    Feb 7 at 14:21
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Catastrophic failure

When high-amperage components fail, it usually comes with some type of internal warping damage due to the higher current, which then generates heat, warps the circuitry, and causes more damage until the circuit breaks*.

I recently serviced a kettle that had a neutral give out. It shows clear heat damage due to warped plastic and metal, and ultimately disintegrated the neutral line inside the kettle. The cause was most likely oxidized welds that increased resistance and started the chain reaction. The kettle was most likely still functional right up to the wire disintegrating.

The breaker isn't going to trip because it isn't taking more power than expected. But instead of heating the water, it was heating up the wire. As far as the panel was concerned, the heater is drawing normal amounts power because it wasn't a ground short. It was a controlled internal short of some type, which is basically what all heating elements are.

*: This is assumed to be a properly made (certified) device. This specific type of failure is called fail open, meaning catastrophic failure results in the device's circuit opening (disconnecting). This is in contrast to fail close, which creates a short, turns the device into a giant heat source, and burns the house down.

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    Thanks for everyone's response. These seem like very likely solutions to my questions. The breaker never tripped, but that makes sense sine the element is just a big resistor and then the wire became the resistor.
    – JBurt
    Feb 6 at 22:16
  • Is fail open vs fail close something we can do anything to influence the odds of? I imagine UL certified devices are engineered to fail open in most cases of catastrophic failure?
    – cr0
    Feb 7 at 1:27
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    @cr0 It is a basic requirement for any respectable certification of electrical devices. That's why it is extremely important to get certified equipment. Even light switches are required to be fail open so it doesn't burn your house down. It is also why the cheap electronics are so dangerous on Amazon. It'll work until it doesn't, then it burns your house down, or gives you a live-neutral shock and kills you. AFCI/GFCI won't save you in a live-neutral shock, because killing you is the "normal load".
    – Nelson
    Feb 7 at 1:29
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    And don't think failure modes are rare. If you don't tighten the screws in a light switch correctly (either under-tighten or over-tighten), it'll eventually heat up from the bad connection. Properly certified switches will fail open and it'll stop working. Taking it out will show clear heat damage. Uncertified switches can fail close, the light switch becomes a heating element, and burn up.
    – Nelson
    Feb 7 at 1:32

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