It's not volts but the amps you probably overloaded the circuit. Most standard house current in the USA can provide up to 20 amps of power (standard 120v ac) the safe amount calculated is 80% of that or 16 amps. You can use the other 4 amps but you saw what happened. It was most likely the surge of the Transformer powering up. They use more power when the light first is turned on to power the capacitors and in the case of HPS igniters as well. Your MH and HPS light (well over 400w) runs on 277v ac so the 120v in is stepped up. Then once it's up to temperature it settles down and the amp requirements is less.

Power strips use a 15 amp thermal breaker so most of the time they will trip before the main circuit will.


Did that help?