The utility model relates to an expandable looped network cabinet unit capable of not interrupting power supply at a single side. The expandable looped network cabinet unit is applied to distribution lines which have realized looped network power supply, and has the characteristics of full seal, full insulation, expandability and the like. The looped network cabinet is internally provided with a base bus, a bus to be expanded and a three-position switch, wherein the bus to be expanded is arranged at the other end of the base bus through the three-position switch, the bus to be expanded is connected with a moving contact of the three-position switch, and a static contact of the three-position switch is connected with the base bus. When electrical cabinets are put together, the three-position switch is powered off and the moving contact is struck to a grounding position through switching operation under the condition of not interrupting the power supply, the bus to be expanded and an outgoing line side of the looped network cabinet are ensured not to be electrified and ensured to be grounded reliably, and the electrical cabinets are put together by connecting a bus of the looped network cabinet required to be expanded with the bus to be expanded. Under the condition of an existing distribution network, the expandable looped network cabinet unit provided by the utility model can improve the reliability of power supply, save the investment cost of the distribution network, and provide a high voltage power supply for an emergency bypass operating vehicle.