The invention relates to an accessory device assembly for a low or medium voltage switching device. The accessory device assembly comprises at least a first accessory device comprising a first external housing, first electrical connection means for electrical connection with said switching device, second electrical connection means for electrical connection with outside equipment, third electrical connection means for electrical connection with a second accessory device, first mechanical connection means for mechanical connection with said second accessory device and second mechanical connection means for mechanical connection with said switching device.