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Difficulty: MediumCircuit Faults and Troubleshooting

An electronics technician is troubleshooting a 24 V24\text{ V} direct-current (DC) control circuit that repeatedly trips its circuit breaker due to a suspected short circuit to ground. Arrange the following diagnostic procedures in the correct chronological order to safely locate and resolve the fault.

  1. 1De-energize the circuit and verify the complete removal of power with a voltmeter before connecting test equipment.
  2. 2Perform a visual inspection of the circuit wiring and terminal strips for obvious signs of charring, pinched wires, or damaged insulation.
  3. 3Disconnect individual branch loads and sub-assemblies to divide the circuit into isolated sections.
  4. 4Measure electrical resistance from each isolated branch conductor to chassis ground using an ohmmeter to identify the zero-ohm path.
  5. 5Repair or replace the shorted component and verify normal branch resistance to ground before resetting the breaker and restoring power.

Answer

The correct troubleshooting procedure starts with de-energizing the circuit and verifying zero voltage, followed by visual inspection, disconnecting branch loads for isolation, measuring resistance to ground using an ohmmeter, and finally repairing the shorted component and verifying resistance before restoring power.
Effective and safe troubleshooting follows a structured logical progression: electrical safety isolation must occur first, followed by visual inspection, systematic branch isolation, ohmmeter resistance testing to locate the shorted path, and pre-power verification following repair.

Step-by-Step Solution

1
De-energize and verify zero voltage on the circuit.
Protects the technician from electrical shock and prevents damaging the ohmmeter.
Ohmmeters supply internal sensing voltage and will be damaged if connected to an energized circuit.
2
Visually inspect conductors, terminals, and components.
Identifies obvious burned insulation, pinched wires, or loose metallic debris.
Visual inspection is the fastest and least invasive diagnostic method before mechanical disassembly.
3
Disconnect branch loads to isolate parallel circuit sections.
Separates parallel current paths from one another.
In parallel networks, a single short circuit to ground will reflect across all interconnected branches unless they are isolated.
4
Measure resistance from each isolated conductor to ground using an ohmmeter.
Locates the exact branch exhibiting abnormal near-zero resistance (0 Ω0\ \Omega).
A dead short creates an unintended low-resistance connection directly to chassis ground.
5
Repair the defective component and verify resistance prior to restoring power.
Ensures normal circuit resistance is restored and prevents immediate breaker tripping upon restart.
Verifying high resistance to ground on the repaired branch confirms the short has been eliminated before power is re-applied.

Key Concept

Systematic Isolation and Troubleshooting of a Short Circuit to Ground
Estimated Time:1m 15s
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Topics

Circuit Faults and Troubleshooting

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