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Contact resistance is the resistance presented by a closed contact, a connector interface or a terminal joint. A high value dissipates power as heat at the joint, which raises the temperature, oxidises the surface and raises the resistance further. Contact resistance testing is therefore both a performance check and an early indicator of a fire hazard.
The measurement is normally made with the four-wire Kelvin method, which passes a defined current through the joint and measures the voltage drop across it with separate sense leads so that lead resistance does not enter the result. Switches, relays, connectors, busbars and terminals are tested after mechanical endurance, after corrosion testing or after temperature cycling, since the resistance is the property that degrades first.
NTEK performs contact resistance and millivolt drop testing as part of component qualification, and along with temperature rise testing to confirm that a joint stays within its rated temperature at rated current.
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