6.4.4.3 Use of natural components of the building structure as down conductors

When using natural components of the structure as a down conductor, the number of separately installed down conductors can be reduced or, in some cases, no separately installed down conductors are required.

The following parts of a structure can be used as natural components of the down conductor:

• Metal installations
  These components can be used as natural down conductors provided that the various parts are safely connected on a permanent basis and their dimensions meet the minimum requirements for down conductors. These metal installations may also be incorporated into insulating material. It is not permitted to use pipelines containing flammable or explosive materials as down conductors if the seals in the flanges / couplings are non-metallic or the flanges / couplings of the connected pipes are not conductively connected in any other way.
• Metal framework of the structure
  If the metal framework of steel frame structures or the interconnected reinforcing steel of the structure is used as a down conductor, ring conductors are not required since additional ring conductors would not improve the splitting of the current.
• Interconnected reinforcement of the structure 
  The reinforcement of existing structures cannot be used as a natural component of the down conductor unless the reinforcement is safely interconnected. Separate external down conductors must be installed.
• Precast parts
  Precast parts must be designed to provide connection points for the reinforcement. The precast concrete parts must have an electrically conductive connection between all connection points. The individual components must be interconnected on site during installation (Figure 6.4.4.3.1).
• Façade elements, DIN rails and metal sub-structures of façades
  These intrinsic components can be used as 'natural' down conductors provided that the dimensions meet the requirements for down conductors (subclause 5.6.2 of IEC 62305-3), the thickness is at least 0.5 mm for sheet metal and metal pipes and the electrical continuity in a vertical direction meets the requirements of subclause 5.5.3 of IEC 62305-3.