Today I installed a couple of light bulbs with my friend. The two wires coming from the ceiling we connected to the lamps using connection strips.
On close examination we noticed that one of the wires had a small crack in it - it was maybe one quarter or a third through the diameter of the wire, I cannot say for sure. My friend, who has a lot more experience in electrical installation than I do, said that such a wire is a fire hazard because the crack means the wire has a smaller diameter in that spot than intended and therefore higher resistance and it therefore dissipates power and could get hotter than expected when powered on.
This sounded strange to me but I didn't argue him at the spot because I wasn't sure myself. Now that I think about it I can't say I agree with him: Even if there is a crack across the diameter of the wire, wouldn't this simply mean that there is extra resistance along the length of the wire as a whole (seen from the "root" of the wires in the electrical system) and just mean there is less current flowing in the lamp?
So which one of us is right? Does such a crack introduce a fire hazard or not, and why?