ELECTRICAL question: Voltage to bulb of a 400 watt HPS

I am building a cooltube and am concerned about the wire gauge to the tube (Don't want to start a fire). I know what I will be using should be ample.

12 AWG (12 gauge) rated for 600 volts. 3 conductors with rubberized waterproof sheathing (pricey stuff but want to be safe).

Was just wondering what is the pulse start up voltage and the eventual running voltage I can expect this line to have to handle.

On re-reading this, I decided I should have been a little clearer in my last sentence.

I mean what type of voltage spike does a 400 HPS put out on start up and then while running steadily.

Are trying to figure the amp draw on start up and while running??

12gauge wire is just fine it is rated at 20amps and the 600v rating is ok not a concern for what you are doing.

It's not really a question of voltage, it's a question of current. Voltage will not change. If you have 120V of power, that isn't going to change. What is going to change is the current inrush. not shitting on you or anything, but I recommend studying up on Ohms law. That will help you understand better how your ballast works.

Will anything else be on this circuit? Thats your main question, second how much currant (amps) is the panel providing the circuit, ie what size of breaker. Voltage won't matter unless it is a long run 300 meters or more. If you tell me these I can help you a little better. I'm an electrician so dont hesitate to ask me anything electrical. Good luck with your grow.