The present invention relates to a device including a high voltage apparatus (2') comprising a housing (3') enclosing a fluid for providing cooling and/or electrical insulation of the apparatus, and a detector equipment (5') adapted to detect one or more physical properties of the fluid and positioned spaced apart from the housing, and the device comprises a pipe assembly (6') for housing a fluid, whereby the pipe assembly is arranged between the detector equipment and the housing such that the fluid is extended without interruption in the pipe assembly, the fluid in the pipe assembly is in communication with the fluid in the housing, and the detector equipment is in direct communication with the fluid in the pipe assembly. The detector equipment is positioned below a top level (20) of the housing and at a safe distance from the housing of the apparatus, which makes it possible to carry out inspection, testing, maintenance, and calibration of the detector equipment without taking the high voltage apparatus out of operation.