How to Read a Contactor Wiring Diagram

Contactor wiring diagrams are needed for reading the connections in the circuits of industrial equipment. Whether you are merely installing or doing troubleshooting, or whether you need to do repair work on the electrical system, it is useful to know how to read these diagrams so you do not inadvertently wreck the system.
A contactor is a part of the industrial or building electrical system switch controlling motor, lighting, or other circuits. It actually acts as a switch opening or throwing the circuit that furnishes the power to the heavy appliance or tool. With the contactor you need only a low-draw signal wire to control a high draw tool.
You the reader will be presented with contactor wiring diagrams probably with one of some 16 of the going-to-be-needed pieces. Familiarity with these will assist you in understanding the drawing.
Contactors have several terminals to which are connected wires; these are usually indicated with either an L for line, or T for load and often C for common. The first step in reading the diagram makes known to the worker which of these wires to place where. Next on comes the coil. An electromagnetic part of the contactor, this receives the low-voltage signal and performs the act of pulling the contactor together or apart, opening and closing the circuit. In the drawing it is indicated usually as a rectangle and possesses two terminals or wires.
An important part of the contractor is the main contacts. As a rule these come in a set and determine a normally closed (NC) or normally open (NO) condition.NO and NC contacts: these are NO contacts ordinarily when the contractor is de-energized; and NC contacts, but are open when the coil is energized.
Auxiliary Contacts: Some contactors are provided with auxiliary contacts which serve for signaling and the like. The result is that other apparatus in the circuit may be made to respond to the operation of the contactor. The auxiliary contacts are shown attached to the diagram with the rest of them.
Overload Relay: It may be desirable at times to connect an overload relay to the contactor for the purpose of protecting the circuit from the danger of an overcurrent condition. This relay is actually wired into the same circuit as the load that it is to protect. It is naturally shown on the diagram with the proper symbols as to how it is connected.
Things we shall do that will make reading a contactor diagram easy:
Find the Power Supply and Load Connections: Beginning, number what terminal of the contactor the live wire (L) is connected to for the purpose of power being supplied to the contactor.Another terminal connected to the load (T) tells you the device the contactor is controlling, motor, light, etc.
Look to the Coil Terminals: Does the control circuit for the contactor seem to be 24V AC or 120V AC? Look for those the terminals clearly marked on the diagram. To these terminals the control voltage is connected to operate with them.
One will typically run to the power source, and run to the switch and then to coil of contactor.
Look up the NO and NC contacts: Go over these with the contactor not energized. NO, contacts are open and no current can flow through them. The NC, contacts are: closed; with the coil energized, the NO contacts are closed and current ifs flowing, while the NC contacts are opened and breaks the circuit.
Trace out the auxiliary: The auxiliary contacts are used to control either other components in the system, or to give certain feedback that the contactor is working. These additional terminals will usually be for the lower power signals or alarms.
Check for overload protection: If your relay diagram shows one, be sure to check the symbol used to indicate the overload protection device. This relay is also wired in series with the load and the contactor and cuts off the power when the current pulls in heavily.
Common Control Wiring Configurations
Single-phase motor control: Wiring diagram for this type of contactor would be a general showing the power supply, the contactor, start and stop switch, and overload relay. The control voltage would normally be wired to a push-button switch that would energize the coil to activate the contactor.
Three-phase motor control: A bit more complicated; here we have several contacts, driven by L1, L2 and L3. There is also an overload relay in series with the motor that provides equal protection for all three lines.
Lighting control: Typical where the contactors control groups of lights, wiring will include contactor, control switch, and possibly an auxiliary contact that will control an indicator or even additional lighting circuit.
Conclusion
It may seem that all this is involved in reading over the contactor diagram the worst kind of double talk; but with at least elder with the symbols, you can do it with ease. From motor to recloser and from industrial to janitor switch your work would quite possibly be dangerous and wasted unless you did understand the symbols and the flow of electricity in the wiring diagram. Remember too, that this is your keyed to troubleshooting and correcting any hazardous condition that might develop.
Knowing how to read contactor wiring diagrams can guarantee proper hookup and maintenance, save you time and trouble. For all your requirements in electrical protection devices such as contactor wiring, check us out or let us know what it is you need and we will be glad to advise you.