The control cable should be protected from damage due to insulation damage, mechanical damage, fire or electrical interference. Dual-protected currents, voltages, and systems that require enhanced reliability, such as DC power supplies and trip control loops, should use separate control cables. In the following cases, the same control cable should not be used together: weak current signal, control loop and strong electric signal, control loop; low level signal and high level signal loop; phase circuit weak phase control loop of AC circuit breaker . The distance between the cores of the same cable is small, and the coupling and electromagnetic induction are strong, which is greater than the interference between the cables. A power plant computer monitoring system analog low-level signal line and the transmitter power line share a four-core cable, causing the signal line to generate a common-mode interference voltage of about 70V, for a low-level signal loop in millivolts, obviously Affects normal work.

Each pair of reciprocating wires of the weak current circuit should belong to the same control cable. The strong electric circuit control cable can be free of metal shielding except for the ultra-high voltage power distribution device or the long-term parallel with the high-voltage cable. 

The control cable of weak current signal and control circuit should be shielded when it is located in an environment with interference and does not have effective anti-interference measures. The selection of the metal shielding type of the control cable shall be included in the comprehensive interference suppression measures according to the possible electrical interference effects, and meet the requirements for reducing interference or overvoltage. The weak current control cable located in the power distribution unit above 110kV should have a total shielding and double-layer general shielding. The monitoring of the signal loop control cable of the computer monitoring system. For the switching signal, the total shielding can be used. For high-level analog signals, it is advisable to use the total shielding of the twisted wire core. If necessary, the twisted wire core can be shielded. For low-level analog signals or pulse quantity signals, the twisted wire core should be shielded. It is also possible to use a twisted wire core to shield the composite total shield. In other cases, the appropriate shielding type should be adopted according to the influencing factors such as electromagnetic induction, electrostatic induction and ground potential rise.

A control cable that reduces electrical interference can be added with a grounded spare core in addition to the number of working cores. When the control cable is grounded, the amplitude of the interference voltage can be reduced to 50% to 25% or more, and the implementation is simple and the cable cost is small. The grounding method of the metal shield of the control cable shall not constitute two or more grounding for the shield of the analog signal loop control cable of the computer monitoring system. It is recommended to use a centralized grounding. In addition, it is necessary to control the cable shielding layer outside the grounding condition. When the electromagnetic induction interference is large, two-point grounding should be adopted; the electrostatic induction interference is large, and one point can be grounded. For double shield or composite total shield, it is better to use one point for the inner and outer shields and two points for grounding. The choice of two-point grounding should also consider that the shielding layer will not be melted under the action of transient current.

If the same round-trip wire belongs to two cables, the possibility of laying a ring is difficult to avoid. The potential of the electromagnetic wire of the similar power source will induce an electric potential, and its magnitude often has a great influence on the interference of the low-level parameter of the weak circuit. If the weak current loop control cable and the power cable can be pulled apart by enough distance, or laid on steel pipes or steel closed trays, external interference may be reduced to the allowable limit. Otherwise, it is generally laid in parallel with the power cable, or in the vicinity of the high-voltage power distribution device and there is a grounding trunk. The interference amplitude is often caused by a low-level signal loop connected to the unshielded control cable. Breakdown and other effects. The control cable reduces the interference when it contains a metal shield, and is related to the shield construction type. At the same time, we must see that the higher the shielding structure requirements, the greater the corresponding investment. The cost of control cables with and without metal shielding is increased by about 10% to 20% (steel tape armor, steel wire braided total shield) or a larger share.

The control cable shield of the digital signal loop of the electronic device should be grounded so that the influence of voltage drop interference on the ground line should be as small as possible. Based on the interference voltage of only about 1V such as a computer, logic errors may be caused, thus emphasizing the calculation and monitoring system. Analog signal loop control cable suppression interference requirements, should be implemented a little grounding, and a little grounding can have a variety of implementations, now in the case of computer monitoring system, indicating that it is to meet the conditions to avoid the occurrence of grounding circulation, centralized one-point grounding. The current distribution of the grounding grid in the power distribution device has been measured to have 13% of the grounding current, and the short-circuit current of the voltage level of 110-500kV has reached 35~18kA.