🔍 Key Concepts

• Mechanical interlock vs. electrical interlock on contactors • How mechanical interlocks are shown in ladder diagrams (often dashed lines between coils or contactor symbols) • Which speeds in a multi‑speed controller must NEVER be energized at the same time

💭 Think About

• Look closely at the lower ladder diagram: which contactor coils are connected together with dashed lines, and what does that symbol represent? • For each speed step (Low, 2nd, 3rd, High), ask yourself which other speed(s) would cause damage if they were closed together, and how the drawing prevents that. • Compare the contactors that share electrical interlocks (normally closed auxiliary contacts) with those that share only a mechanical interlock symbol—can you see which pair cannot be closed simultaneously by a mechanical link?

✅ Before You Answer

• Identify the symbol that represents mechanical interlock (not just a normally closed contact). • Trace which two specific contactor coils are directly tied together by that mechanical interlock symbol in the ladder portion of EL‑0170. • Confirm that those two contactors control mutually exclusive speed connections on the motor—both cannot be on together under any condition.