is (normal) glass an electric insulator, and how much current/p.d would it take for glass to melt?

Question

thank you to everyone that answers

Answer 1

Glass and porcelain are used for electric insulators. The insulator is used to physically support the conductor. The current does not flow through the insulator.

Could a conductor get hot enough to melt the insulator that is supporting it? Not really. The melting point of glass is over 2500 °F. The melting point of common conductors (aluminum, copper, etc) is far lower. The conductor itself would melt down before the insulator would be damaged.

If the current were flowing through the insulator, then you'd have a fault condition and the upstream over-current protective device (fuse or breaker) would clear the fault.