Practical Skills and Workshop Practice
Practical Skills and Workshop Practice tests safe tool use, testing, termination and motor connection in the workshop.
Core rules
- Isolate and prove dead before working; use the correct insulated tool, PPE and lockout tag.
- Continuity testing uses a multimeter or test lamp on a dead circuit; insulation resistance uses a megger at the correct voltage.
- Cable termination: strip without nicking the conductor, fit the correct lug, crimp with the matching die, and torque terminal screws.
- For a six-terminal motor, identify winding pairs with an ohmmeter: U1–U2, V1–V2, W1–W2. Star connection links W2, U2, V2; delta links U1–W2, V1–U2, W1–V2.
- A 415 V motor for star-delta starting runs in delta and starts in star; the star connection reduces phase voltage during starting.
Worked example
A 415 V three-phase motor is to be checked before connection. With the supply locked off, an ohmmeter identifies three winding pairs of about 8 Ω each. For a star-delta starter, the run connection is delta: link U1–W2, V1–U2, W1–V2, and supply U1, V1, W1. The star links W2–U2–V2 are made only by the starter during starting. Insulation resistance from each winding to frame should be at least 1 MΩ at 500 V DC.
Traps
Do not megger a motor with the drive or electronic sensor connected; do not leave terminal links loose; do not assume the star link is the run connection for a 415 V motor; and never test for live voltage with a megger.