PLC electrical wiring precautions

When designing the electrical wiring diagram, refer to the PLC requirements for electrical connections, and pay attention to the following:

1, the wiring diagram requirements

The electrical wiring diagram shall indicate the number, specification and length of each connecting line and the connecting line (including the spare line) in the cable trough, and the external protective measures (such as the type and specification of the metal hose). Length, etc.), standard parts required (such as hose joints, number of pipe clamps, models, specifications, etc.), connectors (such as the type and specification of the plug), etc., in order to guide the construction.

The electrical wiring diagram should accurately, completely and clearly reflect the connection relationship between all electrical components in the system. It should be able to correctly guide and standardize on-site production and construction, and provide assistance for system installation, commissioning and maintenance.

The electrical wiring diagram must not only conform to the schematic diagram, but also the actual connection position and connection requirements of the electrical components, such as the wire number, wire diameter, and wire color.

2, external connection requirements

The armature cables of variable frequency motors and servo motors should be connected by shielded cables to reduce interference with other equipment.

The connection between the electrical cabinet and the equipment of the control system shall have good protective measures. The externally protected metal hose, shielded cable, metal wire trough, etc. shall be used for external protection, so that it has both mechanical strength and damage protection measures. Good shielding.

The connecting cables, wiring tubes, and cable troughs between the electrical cabinet and the equipment must be well fixed by using screws such as mounting screws, hose connectors, and pipe clamps.

The connection between the system cabinet and the equipment should take into account the needs of transportation, disassembly, etc. For the independent accessories in the equipment, the need to separate the separate accessories from the host should be ensured by installing connectors and distribution boxes.

3, internal connection requirements

The layout of the PLC cable must be reasonable and standardized to reduce and eliminate interference in the line and improve reliability. In principle, the connecting cables and cables should be isolated by means of “layered laying” according to the voltage level and the type of signal, and sealed by a metal shield. When the input/output connection cannot be “layered” with the power line, the shielded cable should be used as much as possible, and the shield should be grounded. At the same time, the input signal and the output signal are not declared in the same cable. connecting cables.

Different voltages, different types of signal lines, or power lines and signal lines should be avoided on the same terminal block and the same connector; if it is unavoidable, it should be isolated by the spare terminal and the alternate pin. Prevent short circuits between the wires and reduce mutual interference between the wires.

The cables used for system analog input/output and pulse input/output must be “twisted” shielded wires. When conditions permit, it is best to use “twisted double shielded” cables for connection.

The grounding system of the system must be complete, standardized and reasonable. The connecting line should have sufficient wire diameter. The control part of the equipment should adopt independent grounding mode, and the common grounding wire cannot be used. The shielded wires used in the PLC control system should be grounded properly through the standard "cable clamp" and other devices.

When using an isolating transformer, the connection between the isolation transformer and the PLC power supply is as short as possible to reduce interference in the line. The power connection line of the PLC should have sufficient wire diameter to reduce the voltage drop of the line; the power supply line of the PLC should be “spliced” to prevent high frequency interference. The cable of the PLC expansion unit is a part that is easily disturbed, and the distance from the power line should be 30 to 50 mm.