I can't speak to public street lights...
But I've put up a fair number of parking lot lights.
480, 277 and 208 are by far the most popular voltages used in a commercial setting.
CWA are common as dust. Many are multi-tap so as to handle even 240 and 120. ( Constant Wattage Autoformers )
Public street lights involve much greater distances and may use medium voltages for distribution for that reason. Further, tapping transformers may be SERIES WIRED across the medium voltage circuit -- which then tends to be a RING CIRCUIT.
The above approach is used for runway landing lights. It assures pilots that each and every light -- regardless of location -- taps the exact same amount of medium voltage energy. ( Typically 5,000 VAC )
[ Imagine a stack of Current Transformers all on one 5,000 V conductor. Each would have the same draw/ amperage and voltage imposed because they'd all experience the same field intensity. That's how runways are illuminated.]
Conventional circuits end up faking out the pilots depth perception because they'd have different luminosities based upon how far they were from the distribution node.
Last edited by Tesla; 02/08/11 07:19 PM.
