40 watt transformer - 12 volt. Size of unit is 4 7/8 " x 2 1/2" x 1 3/8". This transformer powers up to 64 12 volt bulbs. Remember to count all your bulbs, not the number of light fixtures, as some fixtures have more than one bulb. These plug-in transformers provide a safe and convenient AC power source for any dollhouse or miniature room. This Cir-Kit transformer is designed to sit on a tabletop. It has the power cord attached. The most popular versions contain a built-in thermal circuit breaker making them virtually burn-out proof. In the event of an overload or short, the thermal breaker simply opens and removes voltage until the unit cools. After cooling, the breaker resets itself and automatically reapplies voltage to the output. U.S./Canadian Transformers These transformers have straight blade pins and are designed primarily for the U.S., Canada, and Mexico, as well as certain other countries, such as Japan.