Complete copper lamp there is no need to ground wire?

Many customers will have such a question when they buy the all-copper lamp of snooker House. Isn't there only 2 wires in general lamps? A fire line, a zero line, directly connected to the power line, why is there a yellow line, what line is this? In fact, the yellow wire seen by the friends is the ground wire. Is it necessary to connect the ground wire? This mainly depends on how elegant the lamps are connected. If it is 220 V, it can not be grounded. For example, most lamps in our country are 220 V, if the lamp is required to be connected to 380 V, it must be connected to the ground. The wire is connected to prevent leakage, and the ground wire is connected to ensure safety.