Question 10 CEL02 - Chief Engineer - Limited (Alt)

The Correct Answer is B **Explanation for Option B (wiping with a clean dry cloth):** Routine cleaning of motor controller contacts (such as those in contactors or relays) should focus on removing light surface contamination (like dust or minor residue) without damaging the delicate silver or silver-cadmium oxide surface. Wiping with a clean, dry, lint-free cloth is the standard, least abrasive method recommended by manufacturers for maintenance when the contacts are still in good condition but require cleaning. This action preserves the integrity of the contact surface, which is crucial for minimizing electrical resistance and prolonging contact life. **Explanation of Incorrect Options:** * **A) dressing with crocus cloth:** Crocus cloth is an abrasive material used for polishing metal. While sometimes used on severely pitted contacts (a practice often discouraged now, favoring replacement), it is *not* suitable for routine cleaning because it removes too much of the critical contact material (the silver/oxide layer), prematurely wearing the contacts and increasing the risk of failure. * **C) filing with a bastard file:** A bastard file is a rough, general-purpose metal file. Filing is a highly destructive method that is never appropriate for cleaning or dressing modern controller contacts. It removes vast amounts of contact material, destroys the factory-engineered contact profile, and leaves behind metal debris, guaranteeing premature failure. * **D) blowing with compressed air:** Blowing with compressed air might remove loose dust but is insufficient for removing most common residues. More importantly, using compressed air can potentially blow conductive dust and contaminants deeper into the mechanism, increasing the risk of insulation breakdown or internal short circuits.