Bathroom ceiling light melted wiring - likely cause?

[FrodoOne]

No-one has mentioned the possibility of a loosely tightened screw on to the red wire. Or am I talking a lot of rubbish?

No, you are not talking rubbish.

However, if it was caused by a loose connection at the screw terminal,
one would expect to see much of the insulation melted close to the connection point,
with less melting further along the wire from that point - due to increasing heat dissipation.

 

[honestworker]

No-one has mentioned the possibility of a loosely tightened screw on to the red wire. Or am I talking a lot of rubbish?

This is a possibility. I found a loose terminal screw on the isolator switch (pull cord type) for an electric shower. The insulation on the wire (feed side, I recall) was well burnt and blackened.