Most Airport lighting for Runways and Taxiways around the world use "Series Loop" lighting. Interesting, after all these years, 6.6 Amp is the standard "high" step on most circuits. We did have some 24 Amp circuits, but did away with because it wasn't necessary. Each light is isolated by a transformer. The transformers are in series and it's a submersible wiring design. Our Airport converted to this back around 1978-79.