What is three wire control of three phase AC motor

 Two-wire control of one or more three-phase AC motors using pushbutton or switches is usually limited to ON / OFF control only. 3-wire control is typically used when there is a time delay between starting and stopping, when an ordered sequence of starting or stopping motors is required, or when some other form of interlocking is required.


Three-wire control of a three-phase AC motor with a three-phase (3-pole) electromagnetic motor starter uses momentary switches with pushbutton or selector switches. A button is a more common option.


Three-wire motor starter solenoid coil control requires two momentary switches: as shown in the following figure, one momentary switch should be in a normally closed configuration at rest and the other in a normally open configuration at rest. The two switches are connected in series with a constant control voltage, usually applied to a normally closed Stop switch. The normally open Start switch is powered (in series with) the normally closed Stop switch.


What is three wire control of three phase AC motor

Two push switches in 3-wire control of a 3-phase AC motor replace the single selector switch contacts in 2-wire control of a 3-phase AC motor. The Start switch is used to start (or enable) the control function. When the Start switch is pressed (or activated), power is supplied to the 3-pole solenoid coil of the electromagnetic motor starter. The solenoid, in turn, supplies power to the AC motor. Since it is a snap-action switch when released, the starter is de-energized and the engine stops.


What is three wire control of three phase AC motor

A sealed circuit is required to keep the 3-phase AC motor running when the Start switch is released. The soldered circuit consists of a set of NO auxiliary contacts on the 3-pole power contactor of the magnetic motor starter (NO contact indicated as M in the diagram), which creates an additional path parallel to the Start switch contacts when closed. When the M close auxiliary contact closes due to the M solenoid being energized from the push of the button (when initially pressed), the Start switch can be released and control power to the solenoid coil will be maintained through this sealed “M” contact. auxiliary blocking. The auxiliary circuit is also called the holding circuit,


The normally closed momentary switch PB in the diagram serves to interrupt (stop or turn off) the control function. If the motor is running, the motor starter solenoid will drop out (de-energized or deactivated) and the motor will stop when Stop is opened. A running state means the Start switch was momentarily closed and the now held closed sealed circuit supplies constant power to the 3-pole solenoid coil of the electromagnetic motor starter and the Stop switch is closed. When the Stop switch is pressed, power is disconnected from the solenoid coil of the motor starter M. Now when released, it returns to its normally closed position. The three-phase AC motor will remain stopped. It remains stopped because both conductive paths (Start switch contacts and NO auxiliary contacts of the motor starter) between the load side of the Stop switch and the line side of the three-pole solenoid coil of the motor starter solenoid (NO switch start contacts PB and the normally open auxiliary contacts of the motor starter) are in the normally open rest position ... To restart the engine, activate (close) the Start switch again.


If the Stop switch is held open (pressed), activating (closing) the Start switch does not initiate the control function: the circuit is disabled. This method of interlocking control is called interlocked stop switching. It is often used to prevent starting a three-phase AC motor during a process cycle.


Like 2-wire control, 3-wire control also gets its name from the number of wires that must be routed from the 3-pole electromagnetic motor starter housing (where the control energy comes from) to the operator's remote control. In the schematic drawing and in the actual three-wire control wiring for one three-phase AC motor, one wire provides continuous power to the fused series switches. It is usually connected to the linear side of the Stop switch.


A second wire from one side of the auxiliary NO contacts of the 3-pole power contactor of the electromagnetic motor starter connects to the midpoint or to the interconnection of the two switches. The third wire, which is the switch foot conductor used to start a three-phase AC motor, connects to the load side of both the auxiliary NO contacts of the motor starter and the Start switch contacts. When these second and third control wires are installed, these two sets of NO contacts are placed in parallel.


On a 3-pole electromagnetic motor starter, a third wire connects the load side of the parallel normally open starter switch and the closing auxiliary contacts of the power contactor of the motor starter to the linear side of the control contacts of the overload relay. The load side terminal of the normally closed contacts of the motor starter overload relay is connected in series with the linear side terminal of the motor starter solenoid coil. The other side or terminal of the motor starter solenoid coil is called the common side because it is connected directly to the # 2 wire: ground or common return of the control circuit.


If the power of the control circuit is not connected to ground (the common side or the reverse side of the control circuit is not directly connected to the equipment grounding system), the control contacts of the overload relay can be connected after the 3-pole solenoid wire of the motor starter solenoid on the common side. The wiring diagram for the power circuit or load circuit for one three-phase AC motor with three-wire control is the same as for two-wire control of the same motor.


Three-wire control has three wires running from the control device to the starter, completing the circuit. Auxiliary contacts have been added to the starters to provide memory for 3-wire pushbutton control circuits. When the motor starter coil (M) is energized, the coil causes the normally open contact to close and remain closed (memory) until the coil is de-energized. Memory is a control function that keeps the engine running after the start button is released. Memory circuits are also known as retention circuits. When a memory circuit is turned on, the circuit remains on until it is turned off, and it remains off until the circuit is turned on again.


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