I found an abandonded hot wire in a junction box in my garage. Someone just cut the wire and left it in the box without a wirenut. Probably been dangling in there for 30 years.

Obviously that is wrong, what is the hazard there for leaving it without a wirenut? Shock or heat?

Also is there any harm in just capping this wire... ie one wire under a yellow wirenut?

 

It should be capped off to prevent accidental contact and a blank plate installed over the box.

 

Its capped, its in a box with about 12 other wires. I wasn't sure if I should go hunting for the other end or not....

So when you cap of a single wire, should I be stripping the insulation before applying the wirenut? That's what I did, the wire was dangling without any insulation stripped so I skinned it like I would if I was making a splice. Figured the spring needed something to bite down on.

 

Doesn't matter if the wire is stripped first, but try it first without stripping the wire in case the single bare wire is too small for the wire nut.