The QO series offers an above-grade transformer that is UL1838 listed for use in landscape lighting systems. The toroidal design offers NO VIBRATION or noise, as well as efficiency ratings in the 95 to 97 percent range, allowing us to offer a 10 year warranty. The QO units come standard with multiple taps on the secondary side, allowing fixtures to vary in distance yet have the same voltage to the fixtures. These taps include 12V, 13V, 14V and 15V. Additionally, we have two taps on the secondary side, one if you are switching the system on and off or a boost tap if connected to a control system or dimmer (compensating for the loss through that device). The QO is available in a single transformer option from 150 to 750 watts. It comes with standard primary and secondary protection. A dual transformer design is available, as well, up to 2 X 300. The housing is available in either stainless steel or a black powder coat finish. Options include a cord and plug for easy setup, an internal astronomical time clock (replaces mechanical clock and photocell), pool and spa listing and custom colors. It is rated for indoor or outdoor use, and is fully dimmable with a magnetic low voltage dimmer.