In our electrical equipment design, the selection of cables is one of the key points, the designer reasonable selection of cables, wire and cable manufacturers that can save equipment costs, improve the safety factor of equipment, improve installation efficiency, the selection of cables generally from the following aspects to consider:

1, conductor material

1.1 Copper conductors should be used for power cables used in the following situations: 1) motor excitation, important power supplies, mobile electrical equipment, etc. need to be connected to high reliability circuits;

2) Vibration place, explosion risk or corrosion of aluminum and other working environment;

3) Fire-resistant cable;

4) Close to the high-temperature equipment layout;

5) Crowded places;

6) Nuclear power plant conventional island and production-related ancillary facilities.

7) Control cable.

Electrical equipment commonly used cables are divided into cabinet wiring, power wiring outside the cabinet, according to the standard, the secondary circuit wiring should use copper conductors, and because the equipment power wiring is generally not long, so generally choose copper conductors.

If the cost pressure of the cabinet bronze plate and transformer is not large, copper is generally selected (like our project, the general owner stipulates that the conductor material is made of copper), which can be selected according to the actual situation of the project.

2 Power cable insulation type

1) Cross-linked polyethylene or PVC extruded insulation type should be used for low-voltage cables, and PVC insulated cables should not be used when environmental protection is required;

2) Cables such as rubber insulation should be used for circuits that often bend and move or have high flexibility requirements, such as mobile electrical equipment.

3) The radiation site should be based on the insulation type requirements, the use of cross-linked polyethylene or ethylene propylene rubber insulation and other radiation resistance cable.

4) In high temperature places above 60℃, heat-resistant polyvinyl chloride, cross-linked polyethylene or ethylene propylene rubber insulation should be selected according to the requirements of high temperature and its duration and insulation type; Mineral insulated cables should be used in high temperature environments above 100 ° C. Common PVC insulated cables should not be used in high temperature places.

5) The annual low temperature below -15 ° C should be selected according to the low temperature conditions and insulation type requirements, cross-linked polyethylene, polyethylene, cold rubber insulated cable. PVC insulated cable should not be used in low temperature environment.

6) In densely populated places or places with low toxicity requirements, halogen-free insulated cables such as crosslinked polyethylene or ethylene propylene rubber should be used, and polyvinyl chloride insulated cables should not be used.

Electrical equipment is generally a low-voltage system, the cabinet wiring is generally selected PVC insulated cable, its main models refer to the following table:

PVC insulated cable model description

BV type wire is harder than RV type wire, in order to facilitate the cabling in the cabinet, the general control cable in the cabinet is RV type cable, and RVV,RVVP,RVSP and other cables can be selected according to the need. Other cables suitable for cabling in the cabinet can also be selected as required. RV cable conditions are as follows:

RV cable conditions

For the output line of the equipment outside the cabinet, the cable that needs to be disassembled frequently is generally selected as YZ,YC type rubber sheathed cable, which is suitable for wiring in mobile occasions.

Conditions for use of rubber sheathed cables

For low-temperature places, YC, RV cables will harden, at this time you can first use silicone rubber cables, but silicone rubber cables are not wear-resistant and cut resistant, pay attention to protection.

The specific cable selection can consult the cable manufacturer, and ask the manufacturer to help select an economical and reasonable cable.

3 Power cable insulation level

The rated voltage of the control cable shall not be lower than the working voltage of the connected circuit, and 450/750V should be selected.

The rated voltage of the cable is expressed as U0/U, where U0 is the voltage RMS between any insulated conductor and ground (the metal sheath or surrounding medium of the cable), and U is the voltage RMS between any two-phase conductor of a multi-core cable or single-core cable system. When used in AC systems, the rated voltage of the cable should be at least equal to the nominal voltage of the system using the cable, and when used in DC systems, the nominal voltage of the system should not be greater than 1.5 times the rated voltage of the cable.

4 Number of cable cores

When the neutral point of 4.11kV and below power supply is directly grounded, the selection of the cable core number of the three-phase circuit shall comply with the following provisions:

When the protective conductor is connected to the exposed conductive part of the electric receiving equipment, the following provisions shall be met:

1)TN-C system, when the protective conductor and neutral conductor are used in the same conductor, 4-core cable should be selected;

2)TN-S system, when the protective conductor and neutral conductor are independent, 5-core cable should be selected; When the requirements are met, the wire and cable can also be composed of a 4-core cable and another protective conductor laid close to the phase conductor;

3)TN-S system, no neutral conductor or the circuit does not need a neutral conductor to lead to the power equipment, should choose 4-core cable; When the requirements are met, a 3-core cable can also be used with another protective conductor laid next to the phase conductor.

4.2 The selection of the number of cores of the control cable shall comply with the following provisions:

1 Control and signal cables should be multi-core cables. When the core section is 1.5mm2 or 2.5mm2, the number of cable cores should not exceed 24. When the core cross sections are 4mm2 and 6mm2, the number of cable cores should not exceed 10.

2 Spare core wires are reserved for the control cables. Spare core wires should be considered in combination with the cable length, core section and cable laying conditions.

3 The following circuits should not use the same control cable with each other:

1) AC current and AC voltage loop, AC and DC loop, strong current and weak current loop;

2) Low level signal and high level signal loop;

3) AC circuit breaker double sets of tripping coil control loop and the phase of the weak current control loop of the phase operation;

4) Star connection and open triangle connection circuit of the same voltage transformer from the distribution device to the relay room.

4 Each pair of round trip wires of the weak circuit should be placed on the same control cable.

5 The three-phase conductor and its neutral conductor from the secondary winding of the same current transformer should be placed in the same control cable.

6 The three-phase conductor and its neutral conductor from the secondary winding of the same voltage transformer star connection shall be placed in the same control cable. The 2(or 3) conductors from the open triangular connection secondary winding of the same voltage transformer shall be placed on the same control cable.

5 Cable Section

5.1 Selection of power cable section

1 The temperature of the cable conductor under the action of the working current shall not exceed the allowable high value of the cable insulation, and the working temperature of the cable conductor in the continuous working circuit shall meet the requirements;

2 Under the action of the working current, the voltage drop of the connected loop shall not exceed the allowable value of the loop;

3 Multi-core power cable conductor small section, copper conductor should not be less than 2.5mm2, aluminum conductor should not be less than 4mm2;

Control cable section selection should meet the following requirements:

1 The current loop section of the protection device should make the error of the current transformer not exceed the specified value;

2 The voltage loop section of relay protection and automatic devices should not exceed 3% of the rated secondary voltage according to the voltage drop of the cable under load;

3 The cross section of the control loop should be based on the voltage drop between the control power bus and the connected cable of the controlled device should not exceed 10% of the rated secondary voltage;

4 The cross section of the strong current control loop should not be less than 1.5mm2, and the cross section of the weak current control loop of the wire and cable should not be less than 0.5mm2;

Qingdao Tianxing Cable Co., Ltd. focus on supporting wire and cable production customization manufacturers, main: exports to more than 40 countries and regions around the world, the annual production capacity of 1 billion yuan. 6000 square meters of storage, standing hundreds of millions of inventory, order demand for rapid distribution and delivery, large prices more favorable. Qingdao cable manufacturer hotline: 16678668098