🔍 Key Concepts
• Identify which devices are in the power circuit (feeding the motor directly) versus which are in the control circuit (feeding the contactor coils KM1, KM2, KM3).
• Trace the control-circuit path from the transformer secondary (X1–X2) through the fuses, switches, and relay/contactor coils to see what actually loses power if a short occurs.
• Understand the specific job of overload relays (OL) versus fuses (FU) in protecting against overcurrent and short-circuit faults in the control circuit.
💭 Think About
• On the right-hand side of the drawing, follow the control-circuit from X1 and X2: which protective components are the first to ‘see’ a short-circuit in that low-voltage wiring?
• If those protective devices open, what happens to the coils of KM1, KM2, and KM3, and therefore to the motor on the left side?
• Compare which listed choices protect the motor power lines and which protect the low-voltage control wiring; which group directly removes power from the contactor coils during a control-circuit short?
✅ Before You Answer
• Verify which fuses (FU1–FU3, FU4–FU7) are on the line side feeding the motor versus the low-voltage control side from the transformer secondary.
• Check which component’s opening would de‑energize the contactors’ coils (KM1, KM2, KM3) even if the main line fuses FU1–FU3 remain intact.
• Confirm the normal function of overload relay OL: does it respond to motor current overload in the main circuit, or to short-circuit current in the control circuit wiring?