What your looking for is called a "High Temp Shut Off Contactor".. Your local grow store should be able to get ahold of one for you.. Its a little box that gets wired in between your timer and the socket you have your lights wired too.. When the temp reaches a certain point.. it cuts the power to the circuit automatically and allows for a "cool down" time in most cases. Check the amp rating.. a safe bet is 5amps per 1000w ballast.. so if you are running 6 ballasts.. you may need 2 x 15amp shut offs.. or 1x30 amp... depending on how you have your room wired ;-) Cheers!