When installing a junction box
for a light or other fixture,
strip the wire first.

Introduction

Before making electrical connections, you'll need to remove some of the sheathing that encases the three or four wires of the cable, and strip some of the insulation that coats the individual wires. Stripping techniques are simple, but exercise care when removing sheathing in order to avoid damaging any of the underlying insulation. Also, be careful to strip the insulation without nicking the copper wire-this would weaken it.

Instead of stripping the wires after the cable is pulled into the box, strip wires before inserting them. That way, if you make a mistake, you can cut off the damaged portion and try again.