In an earlier blog we discussed elements of low voltage lighting such as system design, light placement, and transformer sizing. This blog discusses optimization techniques and secure wiring connections for outdoor lighting.
Details Landscape Art is a Sonoma County landscape contractor. We have designed and installed fine gardens for almost thirty years, and many of our projects include low voltage outdoor lighting systems.The first step in the process is to identify the locations of the various fixtures desired. Then the wattage of these fixtures must be totaled to determine the size of the transformer required. While being sure not to completely maximize the transformer, it’s a good idea to leave some additional capacity in case more lights are subsequently needed once everything is connected and turned on. Sometimes a dark area may want an extra light that was unforeseen originally.
At this point let’s assume that there will be twelve 20w. fixtures installed for a total of 240 watts, and that we will use 12-2 size cable, and a 300w. transformer. If the twelve lights were to be connected sequentially in a line, the last light in the line will be weaker. Distance is the enemy of power. The transformers we use have two ‘Common’ taps and multiple voltage taps. Better to have two separate lines from the transformer with six lights on each line. If the six lights on one line are a long way from each other, that line can be further divided into three lights and three lights or four and two. The more branches of the cable tree, the more the power is evenly distributed. If there are still fixtures that are a long distance from the transformer, then we would beef up the size of the cable to 10-2, which has a larger capacity to conduct electricity.
Secure wiring connections are essential to a long lasting successful system. The 12-2 cable consists of two wires – one hot, one common. We like to separate the strands of each wire in two, and twist each set of strands a couple of turns (see photo). When we insert a fixture ‘interrupting’ the cable, if you will, there are two sections of cable to be connected (before and after the fixture), plus the cable from the fixture itself for a total of three cable sections which means six wires (hot and common for each cable section). As shown in the photo below, each of the twisted split wires are intertwined before being secured with a waterproof wire nut. There will be a wire nut securing the three intertwined wires on the ‘hot’ side and one for the ‘common’ side.We then tape the resulting wire nut connections together using heavy duty black electrical tape so there is no way for the wires to be pulled out of the nuts. Then the entire taped wire nut assembly is staked to the ground underneath the final bark mulch to keep it in place.
These outdoor lighting techniques will result in an optimized and secure low voltage lighting system.