How do I ground a light switch in a plastic box?

The box is not grounded if it is a plastic box.The ground wires must be connected together.In your situation, you will connect the ground from the supply to the fixture using an approved connection.

What happens if you don’t connect the ground wire?Unless the circuit has a ground fault interrupter in it, shock hazard conditions will not cause the breaker to trip unless the ground wire is missing.The appliance ground wire should trip the breaker if the case is grounded.

You don’t have to attach a grounding wire directly to the metal enclosure if you are just using it as a pull point.

There is one green ground screw on the outlet.A pigtail of green or bare ground wire is needed along with the two ground wires.The ground connection for three-prong plugged devices is provided by a grounded electrical outlet.