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Grounding resistance testing, also called earth continuity testing, verifies the protective bonding of a Class I product. If insulation fails, the protective earth path must carry the fault current long enough for the protective device to operate, and must do so without overheating or developing a dangerous voltage on accessible metal parts.
A defined test current, typically 25 A or 10 A from an unloaded source not exceeding 12 V, is passed between the protective earth terminal and each accessible metal part, and the voltage drop is measured. The resistance is calculated from that drop and must not exceed the limit in the relevant standard, commonly 0.1 ohm for appliances to IEC 60335-1.
NTEK performs the test on appliances, lighting, IT and audio-visual equipment, and on power tools and machinery, together with the other routine tests required before a product leaves the production line.