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Let's say we have a 120V cable and a 600V cable, this means that the 600V needs more electrical insulation to prevent the insulator from exceeding its dielectric strength. But in the other case, the 600V needs less heating insulation becauee using P=V.I, and with a constant power, the more the voltage, the less the current, thus plugging it in into P=I2. R , this means less power(heat) is dissipated and more heat is produced by the wire with the lower voltage.

Does this mean electrical insulation and heat insulation are 'opposite'?

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  • $\begingroup$ Wait, why would you want to put thermal insulation around an electrical cable? That would just make it hotter... $\endgroup$ – aquirdturtle Jan 31 at 9:25
  • $\begingroup$ But isn't it a way so that one doesn't accidentally touch the wire? $\endgroup$ – acmilan Feb 5 at 0:53
  • $\begingroup$ The "hot" wire is not actually hot. It has the same temperature as the neutral wire. It is just a metaphorical description of the live lead, the phase wire, the wire that gives you an electrical jolt when you touch it. $\endgroup$ – Pieter Feb 10 at 10:33
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Thicker insulation would be needed at higher voltages if the outer surface is assumed to be at ground potential. A thicker insulation would also lower the risk of electrocution if anyone touches the wire. Remember that overhead High voltage cables are actually bare. Air serves as the insulation. Thermal insulation would depend on the acceptable temperature at the outside of the insulation for a given power dissipation and temperature of the conductor. A nichrome heater used in a water heater used ceramic insulation. So the two (electrical and thermal) are independent.

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You assume that all power is dissipated in the cable, as in case of a short circuit. This requires fire prevention rather than thermal insulation.

In reality temperature of the wire is controlled by giving it sufficient cross section to limit the temperature of the electrical insulation and prevent degradation over time.

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