I like to use a sequence of operation when I describe a control circuit as it some times makes it a little clearer to know what takes place when and how:
Assuming that the overloads have been reset and there N/C contacts are closed as well as the N/C stop push button (red) is also in a normal close state, when the start button N/O (green) is pushed power will flow into the M coil, this will result in the M N/O contacts that are parallel with the start button to hold the circuit in providing power to the coil after the start button has been released, this also closes the 3 N/O contacts that energize the motor or any other type of load, pushing the stop button will remove power to the M coil and it will open the hold-in M contacts thus stopping the motor until the start button is again pushed.
If you look at the B diagram before each of the three N/O contacts you will see what looks like a couple of curves meeting in the middle above each contact, these do not open as they are little heaters that if the motor current exceeds the pre selected heater value will heat up and cause the N/C overload contacts to open and like the N/C stop button will remove power from the M coil thus stopping the motor until the reset is pushed which requires manual intervention so the cause can be determined before the motor is damaged these have to be selected for the FLA of the motor the starter is used for and should be sized at or just above the FLA rating of the motor.
You can have as many control stations as you want by putting the N/C stop buttons in series and the N/O start buttons in parallel, this requires 4 wire run to each control station for more then one control station, but if only one control station is required you only need 3 conductors run to it, the wire feeding the stop button and a wire for each side of the start button back to the motor starter, if pilot lights are wanted then a common (white wire) is needed for the light when the motor is on as the other side can get its power from the last wire connected to the start contacts that runs back to the coil, if a pilot light is wanted to show when the motor is off, then another wire is needed to run back to a N/C contact, the above is for a remote control station.
If emergency stop buttons are needed then these are N/C just like the stop button and also put in series with the stop button, these are usually a mushroom head button that push in and stays in and you have to pull them out manually unlike the momentary stop button, this keeps the machine from being operated when an emergency is required to stop the machine.
As for the colors of the pilot lights, for years I have always use green for run and red for stopped but as in your diagram and at the place I work now we use red for run and green for stopped, not sure if this is something new or just someones idea that green means safe motor off, and red mean unsafe motor on?
Also you will hear terms for the hold-in N/O contacts some will call them lock-in or seal-in contacts, all depends on who you might talk to but they are all the same set of contacts that provide power to the coil after the momentary start button has been released.
