Controlling Voltage for a Better Landscape Lighting

By Mike Gambino

Located in Woodland Hills, California, this backyard tropical pool setting features cross-lighting of several palm species, including Queen, Roebellini (Pigmy Date Palm) and Mediterranean fan. Tree spotlighting comes via brass halogen MR-16 20-and 35-watt flood lamps.
Photos courtesy of Gambino High Performance Landscape Lighting Systems

When using low-voltage lighting systems, voltage loss over long wire runs can quickly become an issue. Multi-tap transformers offer landscape contractors a method for compensating for long-run voltage loss.

Landscape multi-tab transformers play a critical role in larger low-voltage landscape lighting projects. Multi-tab transformers provide a flexible voltage system, which can be adjusted to meet the needs that come from longer wire runs and other factors. Several companies offer multi-tap transformers, including models that run from 11 volts to 22 volts, with 1-volt and .5-volt increment options. The product shown here is the Gambino Magnum, which offers 11.5 to 15 volts at .5-volt increments.

For larger lighting projects, the landscape contractor needs to consider the power and flexibility inherent to a multi-tap transformer. As the name implies, a multi tap transformer is a device that offers more than one voltage output option. These voltage-output choices afford the contractor great flexibility when it comes to providing just the precise voltage for a given project.

Each transformer will have a maximum output, so that all of the items attached to it can’t require more than that wattage combined. To determine the size of the correct transformer, add the combined wattages of all the fixtures, and then divide that number by 0.8. For example, if the lights’ combined wattage equals 220, divide 220 by 0.8 you’ll end up with 275. Choose the next largest transformer. For this scenario, a 300-watt multi-tap transformer would be appropriate.

This Pacific Palisades, California residence features copper spread-lights with 20-watt MR-16 lamps, providing the path-lighting. Statue and tree spotlighting comes via brass halogen MR-16 20- and 35-watt flood lamps, and the down-lighting of the ornament in the background is provided by brass halogen tree-mount down-light with a 20-watt narrow-beam lamp. The power cable was buried six inches below grade inside 1-1/2-inch PVC conduit. 120-volt power comes from two external AC outlets in the front yard. The system is powered by three 600VA variable-voltage transformers, which were hidden behind plant materials. The homeowners control the entire system using a Lightolier remote control unit.

Why Are Multi-Tap Transformers Your Friend?

Voltage drop is an important consideration when specifying low-voltage lighting system equipment. Low-voltage lighting fixtures require 11 to 12 volts at the light fixture. The further the light is located from the transformer, the lower the voltage will be. Larger systems with many fixtures and long cable runs require careful voltage testing at the fixtures. To compensate for voltage drop, multi-tap transformers are used to increase initial voltage output. For example, if one hooks up a light fixture to a 12-volt transformer at the end of 100 feet of cable, the voltage at the fixture could be as low as 9 or 10 volts (a 3-volt drop), thus below the recommended 11-volt minimum. Using a transformer with a 15-volt output, the 3-volt loss results in 12 volts at the fixture (same drop of 3 volts). This is why it is important to use a voltmeter to determine the actual voltage at the fixture, and to use a multi-tap transformer in these systems. Lamp life, lamp brilliance and color are all affected by variances in voltage. When the voltage is too high, bulbs burn out too soon. When the voltage is too low, bulb brilliance and colors are diminished.

Located in Brentwood, California, this residence features up-lighting of Birch, Ash and purple plum trees through the use of 35-watt above-ground halogen up-lights, as well as below-grade halogen up-lights. 120-volt power comes from three separate backyard locations. Two 600VA variable-voltage transformers and one 900VA variable-voltage transformer, power the entire landscape. The system?EUR??,,????'?????<

 

Determining The Right Multi-Tap Transformer

To determine the appropriate transformer size, add up the total wattage of all the lamps and add 10 percent more as a safety factor. (Transformer size = total wattage x 1.1). From here, one can determine the voltage increase to compensate for voltage drop down the line.

Selecting the right cable.

Determine the cable length needed by measuring the distance from your transformer location to the light fixture furthest away from it. Always add a few extra feet per fixture to allow for repositioning during installation. Follow the charts below to select the correct gauge cable. (see chart below)

 

 

Controllers

Photocells and timers are available as transformer accessories. Photocells allow a transformer to automatically turn on at dusk and off at dawn. Timers allow a transformer to be programmed to turn on and off at whatever time you set them for.

Multi-tap transformers offer the landscape contractor flexibility when designing and installing their lighting systems.