Say I need to run a 240 volt circuit that needs 15 amps, would I get a 15 amp double breaker, or would I need a 30 amp? Does the rating assume the amperage to be at 120 volts? As 15 amps at 120 is less power then 15 amps at 240. Also, is it against code to have all the breakers add up to a bigger number then the main breaker? I only have 100 amp service and if I go and add another high amperage breaker I will probably surpass it, if it's not already surpassed. Technically it's safe as if I happen to use all that power at once, the main will do it's job and trip. And one last question, are breakers fairly standard or do I need to get the same brand? My panel is fairly old, it's a Stab-Lok.