Laying of Power Supply Circuit for Fire-fighting Electric Equipment 1.When mineral insulated cables are used, they can be laid directly in the open or in the ceiling. 2.When using non-flammable cables or organic insulated refractory cables, no duct protection (isolation) shall be laid in electric shaft or cable trench. 3.When the line is laid in concealment, the metal conduit or rigid plastic conduit should be protected, and the protective layer should be laid in the non-combustible structure with a thickness of not less than 30 mm.