Fault 01 — NO/NC Swap

Briefing

A motor refuses to start. The electrician confirms the field wiring is correct — both pushbuttons are physically functional. Your job is to identify the logic fault using the scan-cycle highlight and Variables tab, then correct the ladder.

Objectives

• Use slow-scan mode to observe which contact is blocking the rung
• Identify the incorrect contact type (NO vs NC)
• Fix the ladder so the motor starts and seals in on a momentary press
• Verify stop still works correctly after your fix

I/O Table

Your program will be tested against:

All test cases run automatically when you submit. Assertions are hidden until you pass.

1. #1Motor starts on momentary START_PB press

   Press START_PB momentarily — MOTOR_CONTACTOR energises and seals in

2. #2Motor stops on STOP_PB press

   While running, press STOP_PB — MOTOR_CONTACTOR drops

3. #3Seal-in holds after start pulse

   Contactor stays ON after START_PB releases