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Tips for Installing a Low Voltage System
by Chris Desantis
When considering outdoor lighting –whether it be spotlights, ground lights, area lights, deck lights, step lights, etc. we always suggest a low voltage system. And now with LED being perfected for outdoor lighting, it is without a doubt the way to go. The old timers always say “you can’t control voltage drop”, “low voltage isn’t bright enough”, “it’s hard to find fixtures and bulbs and you have to buy a transformer” –but these are all myths with the exception of one. You will have to buy a transformer. But with new technology, the transformers are getting smaller, the lights are getting brighter and the runs are getting longer.
One of the biggest changes in technology (besides LED bulbs) is the multi-tap transformer. The multi-tap transformer allows you to send different home runs throughout your whole yard from one location and tap that area as high as you need to maintain the parameters of the voltage. Halogen light bulbs (usually used for low voltage outdoor lighting) work the best between 11.3 and 11.9 volts (just under 12 volts). And yes, a low voltage 35 watt bulb will be just as bright as a high voltage 35 watt bulb. The trick is getting the 12 volts throughout all your lines without experiencing voltage drop. The more the load and wattage on a line, the more the voltage drop will occur. And there is no way to stop it. So if you can’t beat them, join them. So by being able to start the volts higher at the transformer, it allows you to compensate for your voltage drop. For example, you have a group of 5 spot lights in the corner of your yard approximately 120 feet away. Now with home runs with halogen lights, we would recommend 10 gauge wire. Run the 10 gauge wire to the center of those spot lights using a wiring hub, you can now run 5 12 gauge wires of equal length to each light (if possible). And if there is a 35 watt bulb in each of them, you would be pulling about 175 watts off the transformer. After installing and hooking them up, you would test the voltage at the wiring hub and at the lights themselves. So let’s say, after 120 feet with 175 watts of draw, you are somewhere around 9.6 volts at the hub and each fixture has approximately 9.1 volts. You could now go to your transformer and move the tap leg from 12 volt tap to 15 volt tap or 16 volt tap (which would run a little less than 13 or so at the hub and around 12 volts at each fixture). You never want to go more than 1 or 2 clicks above 12 volts because that would shorten the life of the halogen bulb.
Now we have 35 watt light bulbs at 12 volts running through a transformer and they are just as bright as running a high voltage system. But the biggest difference is that you are stepping it down from the transformer and there is nothing hazardous in your yard. You didn’t have to dig a 1 ½ foot deep trench to meet code and you did not need to put every splice in a sealed wiring compartment. Although that is the only part of a high voltage system that I like, but I will get into that feature being used in a low voltage system soon. But instead you had 2 wires with only 12 volts running through them and there is no code saying where the wire must be run. It can be run between edge line of the grass and walk way out of site or below the flower bed on the side of your yard under the bark. There are no requirements – you can place it where ever you please in your yard. Most people run it in flower beds or edges where it can be easily concealed with bark, topping soil, wood chips, etc.
The run above is what is called “running them in parallel”. The other way you can run your low voltage system is “in series”. Basically, what that means is that you are looping one fixture to the next and the next and the next and so on. Keeping the voltage within the parameters can be done depending on the length and draw. The same run may have multiple home runs. For instance, you are running your system for the same 120 foot side walk, which is a winding pathway that leads to your retreat in the back of your yard. So with a multi-tap transformer, we always start on the 12 tap, run your home right out to your first light in the series. Again, we recommend using a wire hub stake, but explanation is for another time. You then slice the loop and wire your first light into your home run, energize the run and check the voltage at your first light. If it’s below 11 volts, then you know you are going to start on the 13 tap on the transformer at least. Now turn off your transformer, hook up the next few lights in the series, repeating the same process with the loops and then go back and check your voltage at the first and last lights in your line. A multi-tap transformer is designed to keep you within your voltage parameters within 1 volt. So you first light on the home run, should be as close to 12 volts as you can make it without going over. And within this run, the last light must be above 11 volts. If you have not covered the distance of your run and have more than a 1 volt difference between the first and last light of your run, it’s time to add a new home run for a new series of lights to complete the distance of your intended run. They will appear to be on the same run and series, but in reality, you have more than one home run so that your lights are shining as bright as they can be. This is the proper way to run your low voltage system in series.
These are just a few tips of how to install a couple of different low voltage runs. Stay tuned next, we will get into wiring options and parts to use and products that will make your life so much simpler (at least when it comes to lighting).
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