Cable types and selection calculation (electric boiler cable selection) 1. Definition and classification of cables Broadly defined wires and cables are also referred to as cables for short. Cables in a narrow sense refer to insulated cables. It can be defined as: an aggregate consisting of the following parts, one or more insulated cores, and their respective possible covering layers, total protective layer and outer sheath. Cables may also have additional uninsulated conductors.

Wire and cable products are divided into the following five categories according to their use:
1. Bare wires 2. Winding wires 3. Power cables 4. Communication cables and communication optical cables 5. Wires and cables for electrical equipment The basic structure of wires and cables: 1. Objects that conduct current with conductors , The specifications of wires and cables are expressed by the cross - section of the conductor. 2. The insulation material of the outer layer of the insulation is based on its withstand voltage . Φ ) P- power (W); U- voltage (220V); cos Φ - power factor (0.8); I- phase line current (A) three- phase I=P ÷ (U × 1.732












× cos Φ )
P- power (W); U- voltage (380V); cos Φ - power factor (0.8); I- phase line current ( A ) . The safe interception capacity of aluminum wire is 3-**/ mm2. In a single-phase 220V line, the current per 1KW power is about 4-** , and in a three-phase circuit with three-phase load balance, the current per 1KW power is about 2A . That is to say, in a single-phase circuit, every 1 square millimeter of copper wire can withstand a power load of 1KW ; a three-phase balanced circuit can withstand a power of 2-2.5KW . But the greater the working current of the cable, the smaller the safe current it can withstand per square millimeter. The safe working current formula allowed by the cable: Ten under five (ten and below multiplied by five) hundred and two (a hundred and above multiplied by two) two five three five four three circles (two five multiplied by four ,