What type of substrate connection is preferred when using high voltage holiday detectors?

The preferred type of substrate connection when using high voltage holiday detectors is a direct connection to a metal substrate. This is because high voltage holiday detectors operate by applying a high voltage to the probe and checking for holidays (gaps or defects) in coatings, which may allow corrosion to occur on the underlying substrate.

When connected directly to a metal substrate, the detector can effectively sense any defects in the coating, as the electrical current will complete the circuit through the defect, indicating its presence. This direct connection ensures that the detection process is both accurate and efficient, allowing for a reliable assessment of the coating integrity.

In contrast, connections to non-metal surfaces, such as wood or through insulation material, may not provide a complete or effective electrical circuit for the detection process, leading to potential false negatives or inaccurate readings. Therefore, ensuring a direct metal connection is critical for reliable performance when using high voltage holiday detectors in coating inspections.