What does it mean that a nicked conductor can act as a fuse?

from the electrical section- “Any conductor that has been nicked (cut, scratched, incised, or damaged) as the insulation was removed is now of a smaller diameter than intended and has a higher resistance to the flow of electrons.This higher impedance is just the same as having too small a conductor on the circuit, since the damaged area will be the weak link and may either act as the fuse or over heat.”

Think of an automotive-type fuse. The narrowed metal strip is specifically designed to melt at a certain level of current flow. If a fully intact wire can handle a specific amount of current, any narrower (nicked/damaged) portion will handle less than that. Therefore that area of the conductor becomes a “fuse.”



And, you don’t want that defect un-reported nor un-repaired. :+1:


If more electric current flows through a fuse than it was designed for, the fuse heats up so much that it melts. This opens a gap in the Fuse and stops the flow of electricity.
HEAT is the qualifier.
As with a Fuse. In a circuit cable conductor, be it copper or aluminum, a lot of heat is produced at the nick in the conductor. When/if the material melts a gap is created but this does not happen all the time. Question is, can that heat cause a fire? Moreover, the breaker might not trip due to the reduction is AWG size at the nick.

So consider AWG- American Wire Gauge.
14-gauge copper conductor is used for light fixtures, lamps, lighting circuits terminating onto a 15 amp breaker. 12 AWG, American Wire Gauge for 20 amp. 10 AWG, American Wire Gauge for 30 amp. 6 AWG American Wire Gauge for 40-50 amps.

A nick in a 14 AWG conductor reduces the AWG to 16 AWG at that point and posable a higher a number of AWG. The higher the number the thinner the conductor.

This is great in theory but not so much in practice. There is a 20% safety margin in most electrical ratings by the NEC. The copper wire nick (depending on severity of course) does not behave entirely like a fuse (different material) and may only derate the wire to its NEC rating. There are very few places in a home where you will actually be able to see where the wire strip occured.


Nice post Bob. I agree, from an electrical standpoint a nick in the conductor isn’t going to do anything to current carrying capacity of the conductor. A large gouge where a significant amount of metal is removed may be a different story.

I would be more concerned with someone deeply ringing a solid conductor with their pliers and then installing it on a device like a receptacle where the conductors are severely bent when being installed in a box. That weak point could break upon installation of the device.