Auxiliary wire, flat cable and round cable

An auxiliary wire, comprising:

• an auxiliary wire core, comprising one wire core or being formed by twisting a plurality of wire cores;
• a loose jacket protective layer, wherein the loose jacket protective layer sleeves outside of the auxiliary wire core and is able to slide along a length direction of the auxiliary wire core relative to the auxiliary wire core;
• the loose jacket protective layer is formed by tube extrusion of polymer materials or by winding a steel wire around the auxiliary wire core.