If you use a standard "dual output" transformer, that is doublespeak for a Center Tapped Secondary. You can control your circuits with 2 relays in the secondary lines to your lights, that way the neutral/common of your #8 carries zero current, assuming that both strips of lights are the same wattage. This is just like 1 phase 120/240 V. services, which are created by a 240 V. center tapped secondary where the neutral carries only the difference between L1 & L2 current...basic transformer theory.
My experience with LV lighting is that your copper losses (i.e. voltage drop), are excessive @ 12 V. and I have found that 25 amps over 60 feet distance (120 ft. circuit length) of # 10 will only give you about 11 volts across the filaments...your bulbs will last longer, and the wire won't ever freeze in the winter. I x R of supply and return length gives you volts drop, # 8 should be adequate.
If the customer wants a dimmer on these two circuits of lights, this could be interesting...hope it's T & M...
[This message has been edited by Almost Fried (edited 09-15-2006).]
[This message has been edited by Almost Fried (edited 09-20-2006).]
