Welcome pontiacman,
From what I read, and this is what I've been doing, 1440W is the 80% mark. Problem is, i need to unscrew them one at a time and see for sure what's on each circuit. These old houses were wired before we had a ton of wattage to plug in. right now, I don't know if the kitchen is on same circuit as the upstairs bedroom. All I know is the outlet I'm using for my grow is not overloaded. it's got one 630w, one 400w hps, and two 6 inch exhaust fans. And veg tent has one 2 foot, 4 bulb T-5s (maybe 100w). And that's it totally. Like I say, i just bought a 315 sun system, and I'm waiting for it to be repaired or replaced, as it was defective, right out of the box. But adding the 315w, I think will need a different circuit. I've not been feeling well, so I haven't troubleshot the circuits yet. I'm gonna unscrew them one at a time, and see what's on each circuit. I may have to run an extension cord for the 315w ? I've been running the same set up for 2 years and never a problem.
Anyhow, welcome to my little grows. The 630w tent is at 26 days bloom, while the 400w tent is at 10 days bloom. they're all healthy at the moment. Now that summers over, I'll be posting more . You got a journal going ?