hey Im a qualified electrician by trade and I too, use and have built my own contactor board. your problem wont be with the contactor a you can get contactors up to X amount of amps. but your problem will be with the breaker your socket goes too. lets say you have all x4 600s or even x3 600s switch on at the same time each one (unless digital) will fire 6-7amps at the same time for about 3 minutes or how ever long the lamp takes to be fully powered. so at one time you will have 21 or 24 amps being used in one hit. plus any other electrical equipment for the grow, fans etc usually add up to another 5-7 amps and lets not forget any equipment around the house that shares that breaker. the majority of house hold breakers are 16 amp. the shower about 32 and the cooker ( if electric ) is 64 amp. then there is also the gauge of the wiring your using. a standard twin and earth wire will heat up and eventually burn out using that amount of current. my set up is like this. 80amp Breaker --- 10mm twin and earth (fully insulated) --- 50amp contactor with x10 HID Dedicated sockets running through a grasslin timer then x2 full time sockets for other equipment that doesn't require the timer, I have also ran wiring from the living room breaker to an extension lead for the low powered pumps, that have been wired in parallel so on require one plug
if your planning on using 3 or 4 600s check the breaker running that part of the house as if its 64 amp the wiring will have been sufficient to handle those loads and you will be fine. if not id look into installing an extra breaker and wiring the grow your self.. il post some pics of my set up. P.S Contactors are there to switch the timer so you don't blow it that's all, if the current is higher than the rating of the breaker the switch will flip. if the current is higher than the contactor it will flip its switch..
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