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Industrial Control Wiring Guide 2 2010 Part 9

Tham khảo tài liệu 'industrial control wiring guide 2 2010 part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 7. HARDWARE End stops are used to clamp the terminals together. An earth clamp terminal will also do the same job. An insulating end cover plate will be needed at one end since the terminals are open on one side. Identifying numbers can be clipped to them normally matching the wire indents. Warning covers to minimise shock risk should also be used to cover terminals carrying more than 100 V. 74 7. HARDWARE 7.4. Screw terminals 7.4.1. Barrier strips These are used mainly on sub-assemblies to allow them to be connected into the system. Others have screw terminals at both sides and can be used to join wires or as a substitute for the snap together terminals in small low power assemblies. The simpler type have no clamping plate. The wires should be stripped and twisted but not tinned before inserting under the screw heads. Trim off so that the conductor does not go more than half way through the connector. Single strand wire should be folded back to give additional thickness. Avoid overtightening the screw because this can crush the strands and give a weak connection. Barrier strips with clamping plates provide a secure and electrically sound termination. 75 8. COMPONENTS ACTIVE 8.1. Contactors and relays These are mechanical switching devices whose operation is controlled by an electromagnet. The electromagnet consists of a coil of wire with many turns wound on to an iron core. When the coil of the electromagnet is energised the core becomes magnetised and attracts a moving armature. The armature is mechanically coupled to a set of electrical contacts. When the armature is attracted to the electromagnet these contacts operate and complete the circuit. As soon as the coil is de-energised the contacts return to normal usually under spring. Although relays and contactors use the same basic principle of operation the way they achieve the end result is mechanically different. Relays usually have a hinged armature whereas contactors usually have a stronger solenoid action .