The combinable variants are equipped with knock-out membranes which are closed by double membrane seals or sealing and insulating plugs. Protection class II with protection class IP65 is guaranteed. The AKL models can be used in combination with each other. The boxes can be closed with a grey or a transparent cover. Due to the properties of the material, the industrial empty housings are suitable for outdoor use. Four materials are used on this Spelsberg product: Polystyrene, polyurethane, polyamide, glass-fibre reinforced and polystyrene.