The purpose of electrical boxes Wiring connections—where wires join an outlet ... Indoor nonmetallic boxes are typically plastic or fiberglass. Cheap PVC boxes like the one shown at far right ...

Mistake: No electrical box | Never connect wires outside of electrical boxes ... Mistake: Unprotected cable | It’s easy to damage plastic- sheathed cable that’s left exposed between framing ...

Now, the outside of electric wires are usually covered in plastic because it’s a very poor conductor. It hardly conducts any electricity at all, so we can say it’s an electrical insulator.