What are the cables on the bus used for?

That is called a collector pole. The tram is connected to the wire through the "collector pole". The top of the collector rod is usually a sheath with a tunnel containing graphite that allows the cable to slide through. The collector rod is usually placed on a spring seat on the roof of the tram. The tension of the spring presses the collector pole under the overhead wire, ensuring that the two will remain in contact.

The wooden collector pole will have wires that transmit current into the car. If the collector pole is made of metal, it may be insulated at the spring seat and the pole itself is used to transmit electricity. The collector pole can be raised and lowered using a rope placed at the rear of the vehicle. The rope is connected to a spring trap to prevent the collector pole from springing upward when it goes offline.

There are also collector poles without ropes. The lifting and lowering of the pole requires manual work using a long bamboo pole with a hook. Trams generally require only an overhead cable and collector pole, and they use steel wheels and rails to complete the circuit. Trolleybuses usually require a pair of collector poles and cables. One of the cables is not live and is only used to complete the circuit. Before there were collector poles, some trams used collector wheels to obtain electricity. The collector wheel is like a small car suspended under the overhead cable. It is pulled by the tram and uses the wire to transmit the current to the car.

Only trams (including trolleybuses and older trams) still use collector poles. Generally, electrified railways and light railways use newer pantographs. The design of the pantograph is more complicated than that of the collector pole, but the advantage is that it rarely goes offline and is very stable when traveling at high speeds; the pantograph is automatically raised and lowered mechanically, so it is suitable for use on high-voltage cables.

Extended information:

Trolley bus definition and concept

1. Safety Industry Standard of the People's Republic of China and the Government of the People's Republic of China GA 802-2008 " Trolleybus definition in "Motor Vehicle Types Terms and Definitions" (mandatory):

A non-track load-carrying road vehicle powered by an electric motor, connected to a power line, and having four or more wheels.

2. The trolleybus concept of the Urban Construction Industry Standard CJJ/T 114-2007 "Urban Bus Traffic Classification" (Recommended for Implementation) of the People's Republic of China:

Electric bus passenger vehicles that are usually powered by external overhead transmission lines (can also be powered by high-energy batteries) and do not have dedicated tracks.

3. The definition of trolleybus in the Construction Industry Standard of the People's Republic of China GB 5655-1985 "Common Terms and Terms for Urban Bus Transportation" (mandatory):

Trackless electric public transport vehicles powered by external transmission lines.

4. Dual-powered trolleybus (dual-powered trolleybus) in accordance with the Construction Industry Standard of the People's Republic of China GB 5655-1985 "Common Terms and Terminology for Urban Bus Transportation" (mandatory implementation) ) Definition:

A trolley bus powered by batteries or driven by an internal combustion engine on a road section that is separated from external transmission lines.

Reference materials:

Pantograph-Baidu Encyclopedia