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I am considering a purchase of a clap meter but its initial purpose would be to test a circuit branch that is an ancient armored cable without ground, aluminum wire, cloth insulated (the house was built in 1909). I am curious whether the clamp meter will work through metal sheathing.

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up vote 9 down vote accepted

Clamp meters need to be clamped around a single conductor, they will not work if clamped around the entire cable. You would need to clamp around a place where a single conductor is exposed without the metal armor, usually in the main breaker panel or at a receptacle, switch or junction box.

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