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How to Choose the Right Electrical Transformer

Buyer's Guide: Transformers

Transformers are required if you are installing low voltage indoor or outdoor lighting. In the United States, the standard electrical output is 120 volts, so if your lights are a lower voltage, you will need a transformer.

More Than Meets the Eye

The transformer box attaches to your home’s electricity and converts electricity from this high voltage to a lower voltage for use in many outdoor landscaping and track lighting projects.  Transformers typically use a system of electromagnetism and coils to step down the voltage. For outdoor lighting purposes, transformers reduce standard voltage from 120 volts to 12 volts.

A Little Addition

First, you will need to determine the transformer size you will need. To do this, add up all the wattages of all the lamps you plan to use. If you wish to illuminate more watts than the transformer is rated for, simply add another transformer.

Hinkley Lighting Stainless Steel Transformer

Plan Your Layout

Second, you will want to plan your layout. When you install your lights, you may notice that the lights furthest from the transformer are not as bright as those closest to it. This is called “voltage drop” and can be minimized by using a heavier gauge cable, reducing the number of watts attached to the transformer or rearranging your layout.

An “I” layout will get the best results from the transformer. In this layout, the transformer is in the center of the lights, so power is evenly distributed to either side.

Also consider where you want to install your transformer. Some transformers are designed to be buried while others should be installed over existing junction boxes.

If you experience excessive voltage drops, you may want to consider multi-tap transformers, which have terminals with varying voltage or can be used to run two lines of lighting. Voltage drops are affected by the number of watts, the length of the wiring, the voltage at the transformer and the size of the wire.

Check for Extras

Many transformers designed for outdoor use also come with a timer, allowing you to set the lights to go on and off at specific times. Others have “photocells”, which automatically turn lights on and off as the sky lightens and darkens.

What wire size do I need to use with my transformer?

Wire size depends on the length of the wire and the number of watts. Use the following table as a guide.

Cable Gauge

100 Watts

150 Watts

200 Watts

250 Watts
















Wiring Into the Lighting Circuit

To wired a low voltage transformer into the lighting circuit you will first need to turn off the power. Then make sure that the input wires of the transformer are connected to the power line using the terminal screws and that the output wires are connected to the low voltage lights. Use terminal blocks to make sure the connection is secure. Some transformers can be wired to the lights and will just be plugged in to a standard grounded outlet.

Read the Warnings

If you are using a transformer outdoors, make sure it is safe for use in wet locations. Pond lights and other water feature lighting may require a special transformer and most transformers should not be used near swimming pools or spas.

Before installing any electrical fixtures, make sure to turn off the power source. Your local electrician can easily install a transformer for you if you feel uncomfortable doing so.

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