Connect the electromagnetic power relay coil terminals A1 and A2 to a control voltage source that matches the coil rating, commonly 24 V, 120 V, or 230 V. The incoming supply phase passes through a start push button and often through a normally closed stop push button before reaching terminal A1, while A2 returns to neutral or the second phase of the control supply.
Route the main power conductors through the high current relay contacts labeled L1, L2, and L3 on the line side and T1, T2, and T3 on the load side. When the coil energizes, the magnetic core pulls the contact bridge downward and closes these power terminals, allowing current to flow to the motor, heater bank, or lighting group.
Include an overload protection block between the output terminals and the motor leads. Thermal overload modules monitor current through bimetal strips or electronic sensing elements and open the control path if the load exceeds the rated value, commonly set between 90% and 115% of motor full load current.
Add an auxiliary holding contact connected in parallel with the start push button. Once the coil energizes, this auxiliary contact pair closes and maintains coil power after the start button is released. This arrangement keeps the relay engaged until the stop button opens the control line.
Use copper conductors sized according to current rating. For many industrial motor starters, 2.5 mm² to 6 mm² conductors carry the load path, while 0.75 mm² to 1.5 mm² conductors serve the control path. Clear labeling of terminals and consistent conductor colors simplify maintenance and reduce connection errors.
Contactor Wiring Diagram for Motor Starter Control and Power Line Connections
Connect the incoming three phase supply to terminals labeled L1, L2, and L3 on the electromagnetic power relay unit. Route the outgoing conductors from T1, T2, and T3 toward the motor starter output. This arrangement allows the relay mechanism to close or open the power path through magnetic coil activation.
Power Line Terminal Layout
Use clearly defined conductor routing between supply, relay device, and motor terminals. Typical terminal mapping follows this order:
- L1 → incoming phase A from distribution panel
- L2 → incoming phase B from distribution panel
- L3 → incoming phase C from distribution panel
- T1 → motor phase lead U
- T2 → motor phase lead V
- T3 → motor phase lead W
Place a thermal overload block between the output terminals and the motor leads. The overload module monitors current through heating elements and interrupts the control circuit once the current rises above the rated level. Motor nameplate current often guides the adjustment dial, usually set around 0.95–1.05 of rated full load amperage.
Control Line Arrangement
Route the low current control conductors through push buttons and auxiliary contacts so the coil receives voltage only during activation. Typical sequence:
- Phase control line → stop push button (normally closed)
- Stop button → start push button (normally open)
- Start button → coil terminal A1
- Coil terminal A2 → neutral or second control phase
Add an auxiliary holding contact parallel to the start push button. After the coil energizes, the auxiliary pair closes and keeps current flowing through the coil path. Pressing the stop button opens the control line and releases the magnetic armature, disconnecting the motor from the supply lines.
Contactor Wiring Diagram with Coil Terminals A1 A2 and Control Push Button Circuit
Connect the control voltage phase to the normally closed stop push button first, then route the conductor to the normally open start push button, and from there continue to terminal A1 of the electromagnetic relay coil. Terminal A2 returns to neutral or the second control phase depending on the supply configuration.
Select the coil voltage that matches the control supply. Industrial panels frequently use 24 V DC, 110 V AC, or 230 V AC. Supplying a higher voltage than the coil rating overheats the coil windings, while a lower value prevents the armature from pulling the main contacts closed.
Push Button Control Line Layout
Arrange the control conductors in a simple sequence so the coil receives voltage only during activation. The basic control path contains these elements connected in series:
Stop push button → Start push button → Coil terminal A1 → Coil terminal A2 → Neutral or return phase
The stop device uses a normally closed contact so the control path remains complete until the operator presses it. The start device uses a normally open contact that briefly closes and energizes the coil.
Add a holding auxiliary contact connected in parallel with the start push button. Once the magnetic coil energizes, this auxiliary pair closes and maintains current through terminal A1 after the start button returns to its normal position.
Use small control conductors sized between 0.75 mm² and 1.5 mm² copper. Keep these lines separate from high current supply conductors that feed the load terminals such as L1, L2, and L3. Physical separation reduces electromagnetic interference and simplifies troubleshooting.
Control Circuit Protection
Place a miniature control fuse or small circuit breaker ahead of the stop push button. Typical ratings range from 1 A to 6 A depending on coil current. This protective element isolates the control line if insulation failure or short circuits occur inside the panel.
Verify operation after assembly by applying control voltage and pressing the start push button. The magnetic armature should pull inward and keep the power contacts closed until the stop push button interrupts the control path and releases the armature.
