ELECTRICAL TECHNOLOGY

MOTOR CONTROL

Candidates’ Name: Alrae Jackson

Candidate Number: 100047
School: Herbert Morrison Technical High School
Teacher: Mr. Brown
Centre: Herbert Morrison Technical High School
Centre Number: 100047
Territory: Jamaica
Year: 2025

SBA (LAB #4)

GRADE: 11Construction
DATE GIVEN: 3/15/2023
UNIT: Electrical Machines
TITLE: Direct-online three-phase magnetic starter with stop-start control stations.

Objectives: The candidate will be required to:

• Identify common electrical symbols used in motor control diagrams.
• Connect starter with remote stop/start station.
• Describe the basic operation of the control circuit and the power circuit for magnetic
three-phase starters and connect circuitry.

APPARATUS:
✓ One three-phase magnetic stater.
✓ Two N.C. push buttons (Stop button)
✓ Two N.O. push buttons (start button)
✓ Connecting wires

TOOL LIST:
Item List Quantity Function
Measuring Tape 1 To measure the length of
conduits & cables required.

Ball-Peen Hammer 1 To knock out openings in

the meter socket &
distribution panel so as to fit
in the conduits ends.

Hacksaw 1 To cut conduits to the

required length

Flat point screwdriver 1 To tighten or loosen the

screws on the circuit
breakers & meter socket
terminals.

Groove and tongue pliers 1 Used to a fix earth lug to

meter socket & distribution
panel enclosures.
 Utility Knife 1 To trim the insulation from
the conductors.

Set Hexagonal Keys 1 To tighten & loosen earth

lug terminals

SCHEMATIC DIAGRAMS:
WIRING DIAGRAMS:
Schematic Diagram:
Procedures:
 • The single stop/start button control circuit consisting of three-phase magnetic starters was
connected according to the schematic diagram.

• The connection was then checked before connection to the supply.

• The proper operation of the stop/start station and the start was then checked.

• Lastly the supply was disconnected.

THOERY:
We can predict how a magnetic field interacts with an electric circuit to generate an
electromotive force (EMF) using Faraday's Law of Electromagnetism. This process is known as
electromagnetic induction. When current flows through the contactor's coil, it creates a magnetic
field that causes the contacts to attract and close the circuit, enabling power to flow to the motor.

TESTING PROCEDURES:
Tests that were done during this Lab:
Earthing Test
Ring Continuity
Polarity Test

Earthing Test:
One lead was attached to one live wire leading through the isolator, while the other was
connected to another live wire. The contactor was then manually closed. A resistance reading
was obtained after checking, signaling a full direction for current flow. The evaluation was
performed on the remaining stages.
Ring Continuity:
• Within the distribution board, the line. Neutral and earth conductors were removed from
their terminals. Since this is a ring circuit there were two of each in the same terminal.

• The low reading ohm meter function was selected on the tester and the tester was nulled.

• To get the reading for R1, in between each electrical wire was measured.

• Between Neutral to Neutral was measured to get the reading for RN.

• Between Earth and Earth was measured to get the reading for R2.

• The first (outgoing) line to the second incoming) earth was connected. The second
(incoming) line was connected to the first outgoing earth.

• The low reading ohm meter was used to test between Line and Earth on every outlet. The
highest reading is (R1+R2) for the circuit. The readings at each of the sockets wired on
the circuit should be according to this formula: (R1 + R2)/4. Each time the value was
deviating by more than 0.5 ohms, the connections at the accessory terminals was
investigated.

• The cross section line between the Line and Earth conductors was removed. The Line and
Neutral conductors were then cross connected. (L1 to N2 and L2 to N1).

• The line between Line and Neutral on every outlet on the circuit was tested. The readings
at each of sockets that were wired on the ring were very similar. The value was found
according to the given formula (R1 + RN)/4. Every time the measured value deviated by
more than 0.5 ohms, the connection at the accessory terminals was investigated.

• After the Line, Neutral and Earth conductors were placed back into their terminals within
the distribution board.
Polarity Test:
Equipment Required:
• Centre – zero galvanometer, mili voltmeter or mill ammeter
• Switches and Wires
• Battery (1.5 or 3V)

Direction of Deflection
Identifying A1, A2, and B1, B2
• Two randomly phase winding terminals were chosen to be named A1 and A2

• The positive terminal of the battery was connected to A1 and the negative terminal was
connected to the A2 through the switch.

• The meter was connected across one of the other two phase’s windings by B phase
randomly.

• The deflection of the meter pointer was observed at the instant of closing the switch.

• The defection was found in the opposite direction, this means that the polarities were B1
and B2 respectively.

Procedure to identify other terminals C1, C2:

 • The first winding with terminals were connected and called A1 and A2.

• The positive terminal of the battery was connected to A1 and the negative terminal was
connected to A2 through the switch.

• The meter was connected to across the third phase winding

• At the instant of closing the switch, the direction of the meter pointer was observed.

• A clockwise deflection was observed, that means that terminal connected to the positive
of meter was C2 and connected the negative terminal was C1.

OBSERVATION:
A clicking sound was heard as the isolator was turned on, this indicated the circuit was active.
The clicking sound continued after pressing the start button, then the motor began to hum. When
the stop button (the red button) was hit, the motor stopped; a clicking sound was again heard
because of the contactors being flung back up. When the switched is flipped on, electrical was
delivered to the circuit, which then flows to the isolator, allowing the current to flow. After the
current was then sent to the start and stop station, which is equipped with a start and stop button.
The contactor’s coil is then energized and a magnetic field is created when the start button is
pressed, which shuts the contactor. The overload draws current, which then flows to the motor,
which turns it on. Lastly when the stop button is hit, the circuit is broken, causing the magnetic
field to fail, the contactors to open, and the motor to stop.

CONCLUSION:
During the motor control lab, the overload, motor, coil, normally closed contact, normally open
contact were used in the motor circuit. The starter was connected with the start and stop button as
shown in the wiring diagram. The start button was pressed to allow current to pass though the
normally closed button on the coil which then passed through the normally closed contact. It was
concluded that in order to operate a motor you need a magnetic starter.
PROOF OF WORK: