What is the lightning/surge interface?
Where a surge from lightning or switching meets the AGL system and is diverted to earth, so the CCR and the equipment on the loop stay within their voltage ratings.
The lightning/surge interface is where a surge from lightning or switching meets the AGL system and is diverted to earth. Long cable runs across an open airfield pick up voltage from nearby strikes, and surges can also arrive through the power supply and control lines.
Surge arresters fitted at the CCR and other specified points stay quiet in normal service. When a surge arrives they conduct, clamp the voltage and pass the energy to the earthing network through short, direct leads, so the equipment only sees a level it can withstand. Earthing and bonding give the surge a path and keep metalwork at one potential; the arresters limit the voltage. A bare counterpoise conductor laid along the cable route, where the design uses one, reduces the voltage induced in the circuit cable and gives surges an extra path to earth. Outdoor airfield work stops when lightning is near, as the site lightning-warning procedure requires.
Brief, high-energy transient. Diverted to earth; the insulation stays intact.
Lasting connection to earth because insulation has failed.
- Identify. List the entry routes: circuit cable, power supply, control and communication lines.
- Fit. Install arresters at the CCR and the other points the design specifies.
- Connect. Run short, straight leads from each arrester to the earthing network.
- Bond. Tie arrester earths and equipment to the same earthing system so nothing floats.
- Inspect. Check arresters, connections and earth resistance, especially after severe storms.
Frequently Asked Questions
Q1What is the lightning/surge interface in airfield lighting?
The point where a surge from lightning or switching meets the AGL system and is diverted to earth. It is made up of surge arresters, their connections and the earthing network they discharge into.
Q2How does a surge get into an AGL system?
Long cable runs across an open airfield pick up voltage from nearby strikes, and surges can also arrive through the power supply and through control or communication lines.
Q3What does a surge arrester do?
It stays quiet in normal service. When a surge raises the voltage, it conducts, clamps the voltage to a level the equipment can withstand and passes the surge energy to earth, then returns to its quiet state.
Q4Why must arrester connections be short and direct?
During a fast surge even a short lead adds noticeable voltage. The shorter and straighter the lead to the earthing network, the lower the voltage the protected equipment sees.
Q5Is a good earthing system enough on its own?
No. Earthing gives the surge somewhere to go, and bonding keeps metal parts at one potential, but arresters are what limit the voltage on the circuit and equipment. The parts work together.
Q6How is surge protection checked?
By inspecting arresters and any status indicators, checking connections and bonding continuity, and measuring earth resistance at maintenance intervals and after severe storms. Arresters are replaced as the manufacturer and design specify. Testing or replacing an arrester means working on the circuit, so the circuit is isolated and proved dead first.
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