Which device will stop the motor shown in...

🔍 Key Concepts

• Compare how fuses protect against short-circuit (very high, instantaneous current) versus how overload relays (OL) protect against long-term overload (moderate overcurrent). • Trace the power path from L1–L2–L3 through the diagram to the 3‑phase motor and identify which protective devices are directly in series with the motor windings. • Look at which fuses are on the line (power) side and which are only feeding the control/transformer circuit; only one set will actually interrupt motor current.

💭 Think About

• If a short-circuit occurs at the motor terminals or inside the windings, which protective device will see the full line current and be the first to open? • Which devices, if they opened, would only shut down the low‑voltage control circuit but might still leave the main power conductors energized upstream? • How does the function of the OL contacts in the control circuit differ from the function of fuses in the line circuit when responding to a sudden, very high fault current?

✅ Before You Answer

• Verify which fuses (FU1–FU7) are physically in the motor power circuit versus in the control/transformer circuit. • Confirm that short‑circuit protection must act instantaneously for very high currents, while overload heaters are designed for time‑delay action on smaller overcurrents. • Check which device, when it operates, actually opens all three phases feeding the motor, ensuring the motor is fully de‑energized during a fault.

Which device will stop the motor shown in the illustration in case of a short-circuit (high current) motor fault? Illustration EL-0080

transformer primary fuses FU4 and FU5

disconnect switch fuses FU1, FU2, and FU3

transformer secondary fuses FU6 and FU7

overload relay heaters and overload relay NC contacts (OL)

🔍 Key Concepts

💭 Think About

✅ Before You Answer