Why don't you try it and give us your feedback. I've seen people using 100 feet of 12 gauge extension cords to power a 1.5 hp pump motor to their above ground swimming pool on a 15 amp breaker, until an inspector one day happen to be driving by and notice it. Although you will be pulling a few more amps than that pool pump motor, you have an extension cord that can handle more amps and a larger breaker.
You started out with a good plan to run two 120 volts branch circuits, why all the sudden you have the urge for 240 volts? Two 1000 watts ballasts @ 240 volts will have the same sum total current (amp) draw of 10 amps through a sub-panel as would be with the ballasts placed on two 120 volts circuits as you described.
Your original plan to run two 12/2 with ground NM-B (Romex) cables to 120 volts outlets as you described is very safe. You may even be able to plug in a 5,000 btu air conditioner (nothing larger than 5,000 btu) to one of the outlets if needed. A sub-panel is only necessary when you are running more 1000 watts ballasts in that room, so bear that in mind if you plan to expand the lighting in the future. Yes you will need two timers (one for each ballast) for now.
Thanks stevie! Ended up going with my original plan like you said and it seems to work perfectly.
Be more specific and I will lay out a connection schematic. Describe this "fuse switch". What is the voltage of the fan? What is the supply voltage?
Go to ebay and buy an Omron H3CA relay. Make sure to include an 11 pin base (if it isn't already combined). Because you are playing with such a low voltage I will suggest to buy it new, not used. It can be powered with any voltage from 12-240V (AC or DC) but if the internal contacts are old and abused by 120V DC (which may be the case if it is used) it may give the low voltage a hard time breaking through the dirty contacts (which cannot be cleaned in the case of this relay). Buy the relay and I will tell you how to wire it. P.S. Omron H3CA's can do any electrical control operation imaginable (no limit). P.P.S. Does your moisture sensor include a set of contacts which open and close a circuit when the desired moisture is achieved? If so, this is a moisture controller with integral sensor. If you want a definite answer you must be 100% specific in your posts.
That's brilliant info thanks, I haven't decided which moisture sensor to buy for the moment, you can see from the choice on ebay, there are many $15 versions to choose from, i have seen some arduino adapters sold with moisture sensors that may have a kind of switch on them, i dont know, it may be better to make the control electronics at home... http://www.ebay.com/itm/Soil-Hygrometer-Detection-Module-Soil-Moisture-Sensor-/281043772532... As you say if there is a reliability/sensetivity risk, it could be good to have a redundant relay also available at a different humidity rating.
You will be O.K. running the 600 watt light (whether it is supplied by a " 1000 watt electronic" [aka ridiculously unreliable crap ballast] and the 8000 btu air conditioner on a 20 amp circuit (no #10 gauge wire necessary, 100 feet of #12 will not cause a significant voltage drop. If anybody says otherwise I will do the voltage drop calculation to prove it). You're ac unit will draw 6.9 amps max at 120V. You're "electronic" ballast can only draw about 9 amps max (that includes power factor losses) if it were to operate a 1000 watt bulb. You will only draw 16 amps max (continuous;the initial starting current of either appliance is not a factor in consideration of the wire size either [thats only considered when supplying a heavy duty motor, not a listed appliance such as a ballast or air conditioner] and 16 amps is the max allowed for a 20 amp circuit).