Reinforcement Bars as LPS components

Introduction:

IS/IEC 62305 suggests the usage of natural components of the structures to be protected as Lightning Protection System (LPS) components. The reinforcement bars in concrete can be used as natural down conductor and natural earth termination components. The connections to reinforcement rods shall be made with the approval of the builder and the concern civil engineer.

Down conductor system:

The reinforcing rods of concrete columns and steel structural frames may be used as natural down-conductors. The electrical continuity of the conductors should be ensured and the interconnections are made by either welding or by using suitable clamps.

Once concrete is filled, we cannot check the condition of the connections and clamps. Hence special care is required for selecting the connectors and all the installations should be documented properly. The lashed joints are not suitable for lightning-current carrying connections due to the risk of the lashing wire exploding and damaging the concrete. So, for lightning-carrying connections welding and clamping are the preferred methods. The materials for such clamps are chosen in such a way that, it does not undergo any chemical reaction when exposed to concrete.

When the reinforcement steel is used as the down-conductor, the rod in the same position has to be used all the way down, thereby providing direct electrical continuity. Where welding to the reinforcing rods is not permitted, clamps or additional dedicated conductors made of steel, mild steel, galvanized steel or copper shall be used. It is recommended that round steel rods of at least 8mm diameter with a smooth surface be used.

This steel structure acts as an electromagnetic shield and protects the electrical and electronics equipment inside the structures from interferences. The current injected into the reinforcing rods will have a large number of parallel paths to the earthing and hence the magnetic field generated by the lightning impulse current in the steel mesh will also be weak due to the low current density. The overall electrical resistance between the uppermost part and ground level should not be greater than 0.20Ω. The measurement can be made by using a testing equipment with four lead configurations by injecting a current in the order of about 10A.

Those conductive reinforced steel in the concrete structure, when properly used, should form the cage for equipotential of the internal LPS.

IS/IEC 62305 lists the following points as advantages of using reinforcement bars as natural down conductor system components.

• The steel skeleton of reinforced concrete serves as an electromagnetic shield and protects the electrical and electronic equipment from the interference.
• The steel reinforcement in concrete serves the purpose of equipotential bonding of the internal LPS.
• As all the equipment and structure are connected through equipotential bonding, no separation distance is needed.
• The use of reinforcing steel as down-conductors reduces the corrosion problems due to external weather conditions.
• For isolated air termination system, no additional down-conductors are required for masts made of metal or interconnected reinforcing steel.

Earth termination system:

For large structures and industrial plants, the foundation is normally reinforced. The reinforcing bars in concrete are considerably more resistant to corrosion than when they are exposed.

Galvanized steel strips, copper and stainless-steel materials can be used as foundation earth electrodes and can be directly connected to the reinforcement rods. The external earth electrodes in addition to the foundation earthing shall be made of copper or stainless steel.

While using the metallic reinforcement as earth electrode, the mechanical splitting of the concrete should be prevented with proper preventive measures.

Conclusion:

Even though using the reinforcement bars has many advantages, it is nearly impossible to determine the layout and construction of the reinforcement steel after the construction phase. Therefore, the layout of the reinforcement steel should be very well documented with drawings. descriptions and photographs taken during the construction.