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Can anyone tell me any possible dangers/risks that could happen if a wire overheats even if it's insulated properly?

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    $\begingroup$ Fire is the obvious risk. $\endgroup$
    – user137289
    Commented Feb 10, 2019 at 9:16

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Answers to your previous posts related to this subject have pointed out that the primary function of electrical insulation is not to prevent electrical overheating. Assuming you now understand that, I will attempt to answer your current question.

The possible risks are overheating causing thermal degradation of insulation leading to failure of insulation to protect against electric shock, short circuits and ground faults.

The primary concern is for electrical insulation being the “victim” of overheating. Overheating can degrade the electrical insulating properties of insulation so that the insulation no longer provides protection against electric shock. If the insulation is between live conductors or between live conductors and ground, its failure could also increase the risk of short circuits and ground faults increasing the risk of fire and shock. Of course if the overheating is high enough it could directly ignite the insulation.

In order to reduce these risks in the case of general use wiring, the principal safeguard is to reduce the likelihood of overheating. This mainly involves using properly sized conductors for the intended currents and coordinating that with properly sized overcurrent protection (fuses and circuit breakers).

Insulation can also be subjected to thermal degradation due to exposure to high temperatures in its environment, such as contact with high temperature external surfaces. If the temperatures are known insulation with an adequate temperature rating should be used.

This only touches on the subject. But I hope it gives you a better understanding.

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  • $\begingroup$ @acmilan Especially these reels with extension cables are likely to overheat when used at high currents while still coiled up on the reel. Here are images: hsa.ie/eng/Safety_Alerts/2014/Electric_Cable_Reel_Alert $\endgroup$
    – user137289
    Commented Feb 10, 2019 at 10:24
  • $\begingroup$ @Bob D , yes, at first I thought wires with more heat production is insulated more to prevent someone from accidentally touching it but I was wrong. I then thought what's the point of insulating(covering the wire with plastic,etc), overheating doesn't just cause injuries but it could cause fire, damaged components, it could even melt the wire itself and obviously the insulation too. Thanks. $\endgroup$
    – user215726
    Commented Feb 10, 2019 at 13:06
  • $\begingroup$ @Bob D, you and Farcher are two of the most well known 'reply'ers here, a month ago I was confused about transfromers and you explained it thoroughly, same until this very day, thumbs up to both of you! Do you remember my transformer question? Haha... $\endgroup$
    – user215726
    Commented Feb 10, 2019 at 13:09
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When electric wires overheat, there are several dangers. As was said, if the temperature is high enough, the rubber insulator may melt away. The melted rubber, if it alights on a flammable substance, may cause fires. But also, the now exposed wire wilol not only be an electrocution danger, it causes current to bleed out to the sorroundings. This lessens the power feeding the equipment as a side effect. Although this was already said. And also, we know that the resistance of a metal depends on its temperature. As temperature increases, resistance decreases. As resistance decreases, current increases. According to Ohms law. In the case that there are electrical appliances or components attached across the wire, the current may go over the set limit and blow the equipment.

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  • $\begingroup$ "As temperature increases, resistance decreases. As resistance decreases, current increases. According to Ohms law. In the case that there are electrical appliances or components attached across the wire, the current may go over the set limit and blow the equipment." The wiring in a normal home does not offer significant impedance or resistance to the current so as the wiring overheats, you would not notice a significant decrease in resistance. The simple answer is the insulation would melt. You would have the opportunity for an arc to happen, causing a fire. $\endgroup$
    – Rick
    Commented Feb 10, 2019 at 21:36