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Refrigeration & Air Conditioning Mechanic Red Seal · Question

A technician is installing a new condensing unit. There is a perceptible tingle when touching the unit's metal casing, even before connecting the main power supply. What is the most likely immediate cause?

If a unit tingles before main power connection, it indicates an external electrical hazard, such as stray voltage induced from nearby power lines, buried cables

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Question: A technician is installing a new condensing unit. There is a perceptible tingle when touching the unit's metal casing, even before connecting the main power supply. What is the most likely immediate cause?

Answer options:

  • Improper grounding of the outdoor unit by the manufacturer
  • Static electricity build-up from packaging materials ✅ A stray current from external sources, possibly from nearby wiring or utilities
  • Residual charge in the unit's internal components

Correct answer: A stray current from external sources, possibly from nearby wiring or utilities

Explanation: If a unit tingles before main power connection, it indicates an external electrical hazard, such as stray voltage induced from nearby power lines, buried cables, or inadequate grounding of other surrounding structures, which can be extremely dangerous.

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