Abstract: The present invention relates to a transformer with a coil body accommodating at least one primary coil and one secondary coil. It is the object of the present invention to provide a transformer which, using the smallest possible amount of high-grade insulation material, ensures good insulation while remaining compact and easily assembled. The object is achieved by a transformer of the above type which is characterized in that the coil body comprises at least one primary part, accommodating the primary coil, and one secondary part, accommodating the secondary coil, and wherein at least one section of the primary part can be covered by at least one section of the secondary part. This section of the secondary part performs the function of the fire-protection housing for the primary part of the transformer.