Questions:
What is the current draw for HID fixtures?
What is the inrush current?
How many fixtures can I put on a circuit?
Answers:
HID inrush can draw upwards of 18-20 amps on a 120v service. This inrush current only lasts for a very small fraction of a second. Its duration is too short a time to trip breakers.
The normal operating current draw for a 150W fixture is 1.4A at 120V and 1.85A for 277V. A 70W fixture will draw .7A at 120V and .3A at 277V.
For a 20A breaker:
ETC's recommendation is no more than 10 150W HID instruments on a 20A, 120V service and no more than 15 150W instruments on a 20A, 277V service. For 70W HID instruments, ETC recommends no more than 15 units on a 20A, 120V service, and no more than 20 units on a 20A, 277V service.
For a 15A breaker:
ETC's recommendation is no more than 7 150W HID instruments on a 15A, 120V service and no more than 10 150W instruments on a 20A, 277V service. For 70W HID instruments, ETC recommends no more than 10 units on a 20A, 120V service, and no more than 15 units on a 20A, 277V service.