🔍 Key Concepts
• Understanding how voltage appears on the line side and load side of an open contact in a control circuit
• Relationship between readings at X1–X2 and the condition of the control transformer and primary fuse
• How voltage should step through the series path: X1 → Stop → Start → M coil → OLs → X2 when the start button is pressed
💭 Think About
• If you truly have 115 VAC across X1–X2, what does that immediately tell you about the control transformer and any fuse feeding its primary?
• In a simple series control circuit, where will you see full line voltage relative to X2 when there is an open contact, and where will you see 0 VAC? Apply that to points 1, 2, and 3.
• Compare the expected voltage at point 2 when the start button is pressed for each possible fault (open transformer secondary, open start, open stop, blown fuse). Which fault would make point 1 hot but points 2 and 3 dead?
✅ Before You Answer
• Confirm that 115 VAC at X1–X2 means the transformer secondary is energized and not open-circuited, and the primary fuse feeding it is intact.
• Trace the control path from X1 through Stop, Start, M coil, OLs back to X2, and predict voltages at points 1, 2, and 3 for each proposed fault.
• Be sure which side of the stop and start contacts terminals 1, 2, and 3 are on, since that determines whether they should be at 115 VAC or 0 VAC when a contact is open.