The earth screen on electric underfloor heating is designed to ensure that if the cable is cut or damaged the system automatically grounds to earth ensuring the RCD will trip out and turn the system off.
The earth screen can take a number of different forms however there are three main constructions. The most basic method is to place the earth wires in a tubular format creating a sock around the inner heating wires, similar to the outer casing on a coaxial cable. An alternative method is to wrap earthing wires or ribbons around the inner cables forming a spiral earth protecting the heating elements. Heat Mat use this design in their Spiral Safety Shield earth on a number of their specialist products.
The final method is to wrap the entire cable construction with a layer of aluminium foil and then use an earth drain wire within the centre of the cable. These 100% aluminium earth shields satisfy all electrical requirements and ensure you do not need to install an earthing grid above your heating system when installing it in a bathroom or other wet room. Heat Mat’s award winning heating mat and cables ranges utilise a 100% aluminium earth shield ensuring the ultimate safety of these systems, it is impossible to cut into the heating wires without cutting through the earth.