Automatic Sequential Starter Panel for Two Three-Phase Motors

Direct-on-line starting a motor draws 5–7 times its rated current; starting two large motors simultaneously can trip the incomer, sag the plant voltage and stress the supply transformer. The industrial answer is sequential starting: motors start one after another with a defined delay, and process logic often requires an order — the downstream machine must be running before the upstream one feeds it. Students learn contactor control in theory but rarely wire a real interlocked sequence. This project builds a demonstration sequential starter panel for two three-phase motors: an Arduino-based sequence controller (or timer-relay logic) drives two contactor+overload starter bays, enforces the start order with auxiliary-contact interlocking, inserts an adjustable delay between starts, and annunciates running/fault states on indicator lamps. A fault on motor 1 blocks motor 2 — exactly the protection behavior real panels implement.

1. The student wires the panel per the supplied schematic: incomer, two contactor+overload bays, control transformer, sequence controller, lamps and push-buttons.
2. Pressing start energizes contactor 1 (if no fault and the e-stop is healthy); motor 1 starts direct-on-line and its auxiliary contact confirms running.
3. The controller starts the inter-start timer; only when motor 1 is confirmed running AND the delay elapses does it energize contactor 2 and start motor 2.
4. If motor 1's overload trips, or motor 1 fails to confirm running, motor 2 is blocked and the fault lamp annunciates — the student demonstrates this on demand.
5. Stop shuts the motors down in reverse order (motor 2 first, then motor 1), matching process-shutdown practice.
6. The test procedure walks through normal sequence, delayed-start measurement, fault injection (simulated overload) and e-stop response for the report.

Tech stack:

• 2 x 3-phase contactors with auxiliary contacts
• 2 x thermal overload relays (sized to demo motors)
• Arduino-based sequence controller (or timer-relay logic variant)
• Control transformer / SMPS for control supply
• Indicator lamps (run/fault per motor), start/stop/e-stop push-buttons
• 2 x fractional-HP three-phase demo motors
• DIN-rail metal enclosure with schematic and ferruled wiring
• Test procedure with fault-injection steps

• [True sequential logic] Motor 2 can only start after motor 1 is confirmed running (auxiliary contact feedback) plus an adjustable time delay — the core requirement of sequential starting, enforced in both logic and wiring.
• [Electrical interlocking] Hardwired auxiliary-contact interlocks back up the controller logic, so no single software fault can start the motors out of order.
• [Thermal overload protection] Each motor bay has its own thermal overload relay sized to the demo motors; an overload trips that bay, blocks the sequence and lights the fault lamp.
• [Adjustable inter-start delay] The delay between motor 1 start and motor 2 start is settable (timer relay or firmware), demonstrating how plants tune sequence timing.
• [Fault annunciation] Green/red indicator lamps per motor plus a panel fault lamp show running, tripped and sequence-blocked states at a glance.
• [Emergency stop with lockout] A latching emergency stop drops both contactors and requires a deliberate reset before any restart — standard industrial practice.
• [Demo motors included] Two small three-phase demo motors (fractional HP) are wired to the panel so the sequence is visible and audible in the demo.

• Wired sequential starter panel (enclosure, contactors, OLRs, controller, lamps)
• Two three-phase demo motors wired to the panel
• Control schematic, wiring diagram and bill of materials
• Sequence test and fault-injection procedure document
• Project report PDF (motor starting theory, sequence logic, interlocking, test results procedure)
• PPT presentation for final review
• Viva Q&A preparation document (DOL starting current, interlocking, overload protection)

• A demonstration panel with fractional-HP demo motors — it teaches the control logic, not full-scale industrial commissioning.
• The demo runs on a real 415 V three-phase supply, which the student's institution must provide; the manual lists the supply and earthing prerequisites.
• 415 V work is inherently hazardous: the manual mandates qualified supervision, and the panel ships with shrouded terminals and an interlocked door.
• The sequence logic is fixed to two motors in the base build; a three-motor extension is listed as future scope.
• Thermal overload relays protect against sustained overload, not short circuits — the incomer MCB/fuse handles short-circuit protection.
• Starting-current measurements need a clamp meter, which the student provides or borrows per the test procedure.