🔍 Key Concepts

• Difference between low voltage release and low voltage protection in motor starters • How thermal overload devices are drawn in schematics versus magnetic overload relays • Relationship between the power circuit (to the motor) and the control circuit (to the coil) in this drawing

💭 Think About

• Look at what happens in this circuit if ship’s power fails while the switch is in RUN. When power comes back, will the motor start by itself, or must someone operate the switch again? How does that relate to release vs protection? • Study the OL devices in both the power schematic (A) and the wiring diagram (B). Do you see heater elements in each line feeding the motor, or separate current-sensing relays? • Trace the path from L1 through the OFF/RUN switch, the M coil, and the OL contact back to the other line. Is there any holding contact from M that would prevent automatic restart after a voltage dip?

✅ Before You Answer

• Be sure whether the circuit automatically restarts after a voltage loss with the switch left in RUN; that tells you release vs protection. • Confirm whether the overload elements are in series with each motor line (typical of thermal heaters) or are separate magnetic sensing relays. • Verify that the symbol labeled OL appears both in the motor power leads and as a normally closed contact in the control circuit; that corresponds to a specific type of overload device.