During a hot skin test, where should one voltmeter probe be placed?

In a hot skin test, the purpose is to measure the potential difference (voltage) between the non-current-carrying metal parts of an electrical device and an earth ground. Placing one voltmeter probe on an earth ground surface is essential because it provides a reference point that is at zero potential. This is crucial for accurately assessing any unwanted voltage that may be present on the device’s casing due to insulation failures or faults.

Grounding is key in electrical testing as it helps ensure safety and proper functioning. By measuring the potential relative to the earth ground, technicians can identify any hazardous conditions that might pose risks to users. This methodology is widely accepted in electrical safety standards for identifying leakage or stray voltages.

The other options do not serve the test’s purpose effectively. For example, the metal casing of the device may carry a potentially dangerous voltage, and insulating surfaces would not provide a reliable reference point for measurement. Plastic surfaces lack the conductive properties needed for a valid ground measurement. Thus, the earth ground option is the best choice for ensuring an accurate and safe evaluation in a hot skin test.