This standard covers electrical and mechanical performance and test requirements for tap changers installed in voltage regulating power and distribution transformers of all voltage and kVA ratings. It covers load tap changers (LTCs), also known as on-load tap changers (OLTCs), which can change taps while the transformer is energized and carrying load; and it covers de- energized tap changers (DETCs), also known as off-circuit tap changers, which may be operated only while the transformer is not energized. For load tap changers, this standard covers both resistor and reactor types. It also covers certain aspects of the attendant tap changer motor-drive mechanism. It does not cover the tap changer control system (manual or automatic).