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Zorluk: OrtaProtective Devices

An electric motor circuit experiences a momentary inrush current of 25 A when starting up, but drops to a steady operating current of 6 A during normal operation. Which protective device is specifically designed to tolerate this brief startup surge without opening the circuit while still protecting against prolonged overcurrent faults?

  1. A
    A fast-acting fuse
  2. A slow-blow (time-delay) fuseCevap
  3. C
    A parallel shunt resistor
  4. D
    A step-down transformer

Cevap

A slow-blow (time-delay) fuse
Slow-blow (time-delay) fuses are specifically engineered to accommodate temporary, harmless current surges—such as inductive motor starting currents—by incorporating a thermal delay element. If the overcurrent condition persists beyond the brief startup interval or reaches dangerous short-circuit levels, the fuse element melts to isolate and protect the circuit.

Adım Adım Çözüm

1
Analyze the electrical load characteristics of the motor.
The motor draws a high transient inrush current (25 A) that significantly exceeds its continuous operating current (6 A).
Inductive loads like electric motors require substantial starting torque and draw temporary surge currents before establishing normal operating counter-electromotive force.
2
Determine the required response time characteristics for the protective device.
The device must absorb brief current spikes without nuisance tripping, yet still interrupt sustained overloads.
Protective devices must match circuit operational profiles to avoid unnecessary service interruptions while maintaining safety.
3
Identify the component designed with an intentional time lag mechanism.
A slow-blow (time-delay) fuse provides the necessary delay for inductive surges while maintaining full overload protection.
Time-delay fuses utilize dual-element or thermal delay construction that allows momentary overloads to pass harmlessly but melts if current remains high.

Anahtar Kavram

Time-delay protective devices and motor inrush current handling
Tahmini Süre:1m 0s
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Konular

Protective Devices

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