The invention relates to a fault detection device and method, and belongs to the technical field of power automation. The device comprises at least one current transformer and an equipment main unit.The equipment main unit comprises a data sampling device, a processor, a display device, and a power module. Each current transformer is connected with the data sampling device, and the data samplingdeice is connected with the processor. The processor is connected with the display device. The power module is connected with the data sampling device, the processor and the display device. Compared with the prior art, the device provided by the invention can accurately judge the type of a multi-point grounding fault of a CT secondary loop, is very convenient and efficient, avoids the power-off and unwinding operations of a conventional method, reduces the labor intensity of a maintainer, and greatly reduces the time of the maintainer in reducing the multi-point grounding fault of the CT secondary loop.