Practice Questions

1.What type of case needs an Earth wire?

Metal cased appliance because charge can flow onto and off of the case

2.How can an Earth wire protect us from an electric shock

Earth wire carries charges from the metal case to Earth. This prevents the build up of electric charge onto the metal case. 

3.Why are Earth wires not needed on double insulated appliances?

Double insulated appliances have a non metallic case, which is an insulator. Electrical charge cannot flow easily onto an off of the plastic case.