The “Across Line Magnetic Starter” is the simplest method of controlling 3-phase motor using a magnetic contactor,

Figure 3: Schematic diagram of the control and power circuits of the “Across The Line Magnetic Starter”.

Control Operation

Referring to Figure 3, after the main circuit breaker CB is closed, the IDLE pilot lamp indicator is *energized (turn on) indicating that the motor is at stand still condition.

Magnetic contactor C, RUN and FAULT pilot lamp indicator are still in the de-energized (turn off) state.

When the START push button is pressed, magnetic contactor C

is *energized.

With contactor C energized, contacts C(1-2, 3-4, and 5-6) will

be closed and they connect the motor M to the 3-phase supply

lines (L1, L2, and L3).

The motor will run (rotate).

Contacts (11-12) will open and make the IDLE pilot lamp de-

energized.

Contacts (13-14) will be closed and maintain contactor C at

energized state even if the push button switch is released**.

The RUN pilot lamp is energized to indicate that the motor is

running (rotating).

                When the STOP push button is pressed, the current through the magnetic contactor C is cut off**.

                Magnetic contactor C is de-energized**.

                Contacts C (1-2, 3-4, 5-6) will open and they will de-energized motor M.

                Contacts C (11-12) will closed and it will make the IDLE lamp energized* again to indicate that the motor goes back to its stand still condition.

                Contacts C (13-14) will open to release contactor C from its maintained energize state.

                The RUN lamp is also de-energized.

                When the motor operates* at more than its rated capacity (overloaded), it will draw an overload current above its rated current.

                The thermally operated device O.L. (1-2, 3-4, 5-6) set to operate at the rated current of the motor will overheat.

                This thermally operated device will expand and push a mechanism that will open the normally closed contacts O.L. (95-96 and will close the normally open contact O.L. (95-98).

                Opening contacts O.L. (95-96) will cut off the current through the contactor C.

                This is similar as if the STOP push button is pressed.

                Closing the normally open contacts O.L. (95-98) will make the BUZZER to alarm and alert an operator that something goes wrong with the operation.

                The FAULT lamp is also energized* and will be lighted.

                The lighted FAULT lamp will inform the operator which motor from a group of motors is at fault.

                The circuit involve in starting and stopping starts from line L1, contact I of contactor C, contacts (95-96) of overload relay O.L., contacts (1-2) of stop push button, contacts (3-4) of start push button or contacts (13-14) of contactor C, contact 3 of contactor C and the line L2.

                Across the Line Magnetic Starter is applied to motors whose locked rotor current is only a few times more than the full load current of the motor.

        * - The terms: energize, activate, operate, run, turn-on, switch on, and start; are sometimes used interchangeably in the proceeding explanation of control circuit operation. The terms are to indicate that a machine or an equipment commence to function and is now taking electrical energy from the source.

        ** - The terms: de-energize, stops, de-activate, turn-off, switch off, cut-off, and released are often used interchangeably. Those terms are used to indicate that a machine or an equipment stops from functioning and taking energy from the source.