🔍 Key Concepts

• Trace where the MS 1 contacts are wired in the control circuit and note which device or coil they energize or de‑energize. • Review the difference between low voltage protection and low voltage release in motor control circuits, and how an undervoltage (UV) coil is usually used. • Consider how the circuit prevents the hoist motor from restarting automatically after a power failure or severe voltage drop.

💭 Think About

• When the master switch handle is moved to any Hoist or Lower position, what happens to the MS 1 contacts, and which relay/coil becomes energized as a result? • If line voltage is lost and then restored while the master switch is left in a running position, what role do the MS 1 contacts and the UV device play in whether the motor restarts automatically? • Do the MS 1 contacts carry the main motor current for overload protection, or are they only in the control circuit for a safety/interlock function?

✅ Before You Answer

• Verify that MS 1 is closed in every Hoist and Lower position, but open in OFF, and see how that ties into the UV coil in the drawing. • Confirm whether the function provided by MS 1 and the UV device is to trip/open the circuit on low voltage and require an intentional action by the operator to restart. • Ensure that neither power factor correction capacitors nor overload heaters (OL) are in series with MS 1, which helps eliminate some answer choices.