Lightning protection grounding for mains powered traffic lights

I. Create a Reliable Earth Current Discharge Channel

Grounding devices are installed together with the foundation construction of AC traffic signal lights, and the grounding electrodes are galvanized angle steel and galvanized flat steel. Each pole is driven into the ground with two galvanized angle steels of 2.5 m length, at least 5 m apart. They are then connected horizontally by 40×4 mm hot-dip galvanized flat steel to form a ring-shaped grounding grid. The flat steel welded joints are all welded and coated with asphalt to prevent corrosion. Burial depth is controlled below 0.7m, avoiding poorly conductive soil layers like gravel and dry sand. Backfilling with a resistance-reducing agent in dry soil areas will decrease the earth resistance. Reinforced concrete cannot be used as a single substitute for dedicated grounding electrodes. Concrete conductivity is unstable and cannot quickly discharge high voltage during lightning strikes.

II. Equipotential Bonding of All Equipment to Avoid Risk of Potential Difference Failure

After the grounding grid has been constructed, the poles, signal boxes, signal light housings, and metal conduits shall be bonded to a common equipotential bonding. The metal pole bases shall be reliably welded directly to the grounding flat steel. Distribution boxes and signal housings shall be connected to the grounding mains using yellow-green bicolor grounding wires. Copper grounding wires shall be connected across both ends of the metal conduits to prevent the conduits from being suspended from inducing voltage. All grounding grids at an intersection shall be interconnected to make one potential body for the entire intersection. This prevents arcing due to voltage differences between different equipment and the ground during thunderstorms and prevents damage to LED light panels and controller motherboards. Plastic-cased signal lights also require the internal metal brackets to be grounded; the internal wiring for the grounding terminals cannot be omitted.

III. Installation of Surge Protectors to Cut Off Induced Lightning Strikes

Surge protection devices shall be provided at both ends of the mains power inlet and signal communications lines. A primary surge protector is separately connected to the live, neutral, and ground wires at the 220V mains power inlet in the traffic signal distribution box. On the network cable and 485 communication control line, install a signal surge protector and connect the metal sheath of the shielded network cable to the ground at both ends. All surge protector ground wires are directly connected to the grounding mains, and the lead lengths are limited to within 0.5 meters to reduce the residual voltage. Priority should be given to converting overhead cable intersections to underground conduit cabling. Overhead lines are affected by induced high-voltage lightning strikes. Underground cabling greatly reduces the chance of lightning intrusion. Cable inlets and outlets must be properly waterproofed and sealed to prevent rainwater from corroding the surge protector terminals.

IV. Periodic Grounding Resistance Measurement and Maintenance After Construction

When construction is finished, the grounding resistance is tested with a grounding resistance tester. Municipal traffic lights at intersections have a standard grounding resistance ≤4Ω. If the resistance is higher than the standard, extra grounding electrodes or resistance-reducing materials should be added. Before each rainy season, conduct inspections to check for rust at flat steel weld points, loose or detached grounding wires, and blackening or failure of surge protectors. Grounding trenches can collect water during the rainy season. Remove it immediately after the rainy season so that grounding electrodes do not stay immersed in water for long periods and corrode. For the old intersections undergoing renovation, the rusty grounding grids need to be refurbished, and the aging grounding wires need to be replaced to prevent equipment burnout and electric shock accidents caused by grounding failure.