Oh yes, this is the age old low voltage lighting question, “Why are my lights dim?” Although there could be a number of reasons for this, the primary and most common culprit is … VOLTAGE DROP.
So, what is voltage drop you might ask? Quite simply, it is energy that is lost along a wire due to friction. As the electricity travels down the wire, it meets up with resistance in the wire and loses some of its power. If there is a load on that wire, it loses even more energy. Each load along the way creates even more friction and takes some of the energy. More loads, more loss of energy.
There is a formula to figure this out which is:
(Watts X Length of wire ÷ Cable Constant) X2 = Voltage Drop.
Got it? Like a lot of scientific formulas, every component is critical information. Consulting the National Electrical Code, and being familiar with wire will be very helpful when utilizing this formula on your own. Professional outdoor lighting designers and installers know this formula by heart.
Most DIY folks who install lighting themselves, often using a box store lighting kit, will run into this problem. The kit instructs the installer to run a wire from the transformer, and connect the light fixtures along the way in what we call the “daisy chain” wiring method. The homeowner finds that the first light is bright and looks good, while each additional light on the chain gets dimmer and dimmer. If there are enough lights on that chain of wire, all of the lights may be dim – and the last light may not work at all. This is because each of those lights along the way takes power out of that wire, leaving less and less energy at the end of the line.
This would be a very long post if I went into each and every scenario of voltage drop and its remedy, so I’ll spare you from that. But I will give you the most common fixes to lessen the effects of voltage drop. First, you may just need larger wire. Next option is to look at a different wiring method. In some cases, you might need to do both.
If you increase the size of the wire, you are allowing the electricity to flow with less resistance and, therefore, lower the amount of voltage drop to each light. Think of water going through a pipe; the larger the pipe is, the easier and faster the water flows through it. When putting on the lights, the “hub” wiring method lets you to distribute the voltage evenly to each fixture; this wiring method would at least make the lights all look the same.
Here are few very important things to remember:
- DO NOT overload the wire you choose to use. Know the amount of load (amps) the wire is rated to handle. For example: 12 gauge wire is rated for 20 amps, 14 gauge wire is rated for 15 amps. Adapt your wiring method and/or number of fixtures per wire to meet the limitations of the wire. By using fewer lights on a wire, you decrease the resistance and lower the voltage drop.
- Be sure to make good, solid, waterproof connections. Those pierce-point connectors that come with that DIY lighting kit will allow water to get into your wire causing corrosion, which in turn will increase the resistance and voltage drop, ultimately ending in system failure.
We use professional series transformers with higher voltage taps, going up to 15 volts, which also help us deal with the very common voltage drop animal. The transformer, the wire, the wiring method and the load all contribute to the voltage drop that we see in low voltage lighting systems. Knowing how to insure that each fixture gets the voltage it needs to operate at its best is where the outdoor lighting professional can really help, saving you tremendous aggravation and providing a well-balanced lighting system that will look beautiful for years.
We do not work on the type of landscape lighting products that can be purchased at the home improvement stores. But if you are in the central Texas/Highland Lakes area and have these problems with a professional grade outdoor lighting system, we would be happy to fix the voltage drop problems for you. Just contact us here.
