A protective cover arrangement (1) for a first electrical unit, e.g. a starter unit (3), mountable on a second electrical unit, e.g. a compressor (2). The protective cover arrangement (1) comprises an outer cover (5) and an inner cover (6). The outer cover (5) comprises mounting parts (8) adapted to cooperate with mounting parts (10) on the second electrical unit in order to mount the outer cover (5) on the second electrical unit. The inner cover (6) is sized and shaped to fit inside the outer cover (5), and it is adapted to accommodate a first electrical unit in an interior part (7). The inner cover (6) comprises an opening (12) allowing electrical connectors (4) to pass from the second electrical unit to the interior part (7), thereby providing electrical connection between the first electrical unit and the second electrical unit. The inner cover (6) further comprises a cable entry structure (9) allowing one or more electrical cables to pass from the exterior of the protective cover arrangement (1) to the interior part (7) of the inner cover (6), thereby providing power supply for the electrical units. The cable entry structure (9) defines one or more cable guides, each defining a curved cable path. The inner cover (6) provides additional protection against moisture and/or dust, and it can be added to the arrangement (1) without significantly changing the design of the other components. It is possible to retrofit the inner cover (6) onto operating devices.