What is a transformer?

There are many type of transformers and they are used for numerous applications. In this article, we will be discussing low voltage transformers approved for lighting loads. A transformer is a device that transforms high-voltage electricity into a safer usable voltage; in this case, it changes the 120V in your home to 12V or 24V to run low voltage lighting.

How do I know what transformer to use?

Check the fixture manufacturer’s recommendations, most will advise you which transformers work best with their product. Low voltage transformers are available magnetic or electronic with 12V or 24V output. Most low voltage lighting will require a 12V output, however, some systems do use 24V transformers and those require you to use 24V light bulbs.

First: calculate your load = number of fixtures x maximum wattage of fixture.

Tip: Always calculate based on the maximum wattage even if you aren’t going to lamp with the maximum, that way you are covered should someone put in a higher wattage bulb in the future.

Important: Low voltage lighting is limited to 300 watts per circuit. This wattage limitation is required by the National Electric Code (NEC) and cannot be exceeded. If your load exceeds 300 watts, you will need to use a dual circuit 600W transformer (2 x 300W) which requires 2 separate electrical feeds.

Second: calculate the distance from the transformer to the load to avoid voltage drop. Certain transformers are better suited for long distance runs than others.

Example: electronic AC transformers have a distance limitation of 5-10 feet; electronic DC transformers are suitable for much longer distances and magnetic transformers can be located up to 100 feet away.

Be sure to use the appropriate wire size for your load and distance to avoid voltage drops.

Third: Select the best option for your application – magnetic or electronic. See more details below…

What are the differences between magnetic and electronic?

Electronic transformers are typically smaller and many fit right in the junction box. They limited to 300 watts per circuit. Most electronic transformers require a load of at least 50% of their output wattage. Because of their electronics can be sensitive to heat. When dimmed some people can hear an electronic buzzing or hum.

Magnetic transformers are much larger and will not fit in a fixture. They are available in two styles: stacked laminated which are square and toroidal which are doughnut shaped. They are available up to dual 600W and many have boost output taps up to 15 volts. Some people can hear magnetic transformers, the totoidal are quieter than the stacked laminated. Sound dimming coils can be purchased separately.

Can I dim a low voltage transformer?

Yes. Electronic transformers require electronic low voltage dimmers and magnetic transformers require magnetic low voltage dimmers.

Can I use them outdoors?

Be sure to use transformers that are rated for outdoor use. Most manufacturers offer outdoor transformers with lighting controls built in, time clocks, photocells or both, which save energy and lengthens the life of your bulb.