I'll be placing a bid for some parking lot lighting at the local Ford dealership, the requirement : 16 - 1000w MH mega floods.

My question.... calculations involved to properly size the lighting contactor?

Sandro:
First, get the ballast info from the fixture mfg. starting and operating amps, at the voltage you have available. Then determine if there are any required circuitry layouts that you have to conform to. Number of heads on each pole, all heads on 1 pole on same circuit, partial or "nite lights", all on at once, or staggered (sequential) starting to conform to any energy codes or job specs.

Without knowing the specs, you can't lay it out.

If you need help, let me know. This is a busy weekend, so I may not be able to get back to you quick.
John