Preface:
This Thread has (finally!) been created for the Discussion of the Start / Stop "3-Wire" Motor Control Schematic, located at the Technical Reference Area - per the listing:

Start Stop 3 Wire AC Motor Control

in conjunction with the Thread:
Start/Stop Motor Control within this Forum Area.

Feel free to contribute to this Message via replies.
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Per the Schematic:

[Linked Image]
Fig. 1.1: Basic 3 Wire Start / Stop AC Motor Control.

This Schematic details the basic method for Starting & Stopping an AC Motor from One Control Station.

The Control Station incorporates Two Momentary Contact Push Buttons:
(1) Normally Closed "STOP" Switch (N.C.),
and
(1) Normally Open "START" Switch (N.O.).

*** Note ***
Any number of Start/Stop Stations may be incorporated in this type of Motor Control. Each Station will contain (1) Stop and (1) Start Push Button.
All "Stop" Switches are in Series with the Motor Starter's Coil Circuit, and all "Start" Switches are Parallel to the Coil Circuit.

----- DESCRIPTION OF OPERATION -----

With the Circuit "At Rest" (Coil is DE-energized, and all Overload Relays Closed), pressing the N.O. Start Switch energizes the Coil of the Magnetic Starter - resulting in the device "Pulling-In", and closing the Motor Contacts.
In addition, the Auxiliary Contact closes, which keeps the Coil energized through the Control Circuit.

Pressing the N.C. Stop Switch temporarily opens the Control Circuit, which DE-energizes the Coil - thereby opening the Motor Contacts and DE-energizing the Motor.
The Auxiliary Contact opens as well, and the device remains "Off" until the Start Button is pressed once again.

If there is an Overload issue, One (or more) of the Overload Relays open, which opens the Control Circuit and drops out the Coil.

This Control will also offer "Under-voltage Protection" when the Coil is driven at the same Voltage of the Motor.
If the Motor Circuit Voltage drops below the threshold of what the Coil can hold the Contacts closed, the Starter drops-out, and the Motor is DE-energized.

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A newer set of Start/Stop Drawings may be viewed at the Technical Reference Area, per the Topic:

Basic Start/Stop AC Motor Control

Clicking on the above link (underlined text) will open that page in a new Tab.

--Scott (EE)

Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!