When are Low Voltage Transformers used in Outdoor Lighting?

Low voltage transformers convert the amount of voltage supplied from one level to another. They are commonly used to convert voltage from a higher voltage system (ex. house current) down to a lower voltage system to supply the correct amount of energy supported by an electronic device.

Without transformers you would certainly burn out whatever electrical devices you wanted to power.

In the United States it's common to find 120 volt outlets in a residential home's electrical supply as is common to find 220 volts or more in a commercial property's electrical supply.

120 volt house current is commonly referred to as line voltage because 120 volts is the amount of voltage supplied to most homes from outside electrical lines. Low voltage lighting uses smaller more discrete lighting fixtures. These fixtures are usually sufficient to supply adequate amounts of outdoor lighting for most needs and make installing outdoor lighting much easier.

Installing Outdoor Transformers

Working with 120 volt systems can cause serious bodily harm so STAY AWAY from installing low voltage transformers yourself.

Unlike 120 volt cables, low voltage outdoor lighting cables are usually run underneath mulch and around your landscape's structures. Much easier than 120 volt lighting where you would have to dig a trench and lay cable underground.

Always check your local municipality codes to find out the proper procedures for running low voltage lighting cables. Some municipalities require that even low voltage lighting cables be buried under ground.

The location of your low voltage transformers should always be within a reasonable distance of the low voltage lighting fixtures you will be installing. The longer the distance is between the transformer and the fixture the more you will experience cable voltage drop.

Cable voltage drop happens when a cable is run between the low voltage transformer and the fixture(s). The voltage at the beginning of the cable is always stronger than that at the end of the cable resulting in cable voltage drop.

Some things that contribute to cable voltage drop are:

2) The number of low voltage fixtures installed on that cable.

3) The cable's thickness.

A cable carrying too little voltage will result in your fixtures not emitting the maximum light output per fixture causing a yellow light output.

There are a number of ways to calculate voltage drop. Some commonly used references are the Electrician's Vest Pocket Reference Book and Ugly's Electrical References.

The best place to install low voltage transformers is indoors. This eliminates the need to protect the transformer from the outdoor elements. It also gives you easier access to the transformer.

Sometimes installing a transformer indoors can cause too much cable voltage drop. Thats why transformers used outdoors can be housed in special weatherproof boxes.

These boxes typically are hidden behind low lying shrubs or bushes. You may also find transformer boxes that are hidden underground in special ground-burial boxes.

Which transformers are right for me?

By knowing the individual wattages of the bulbs being used in your project and the number of fixtures you will be installing on that line, you will have a fairly good idea of the right transformer needed for the job.

The formula to calculate total wattage is:

# of Fixtures X Bulb Wattage = Total Wattage

Transformers are usually available in 50 or 100 watt capacities so always purchase one with some spare wattage. You never know when you'll need to add more fixtures in a changing environment.

Rule of thumb is to leave about 25% spare capacity because leaving too much will result in overvoltage and cause your bulb life to be shortened.

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