When it comes to wiring your lighting system there are several methods commonly used. Some are efficient, while others are touted as “easy-to-install,” but significantly decrease the energy efficiency of your system. In any situation, proper use of these techniques is imperative in order to provide the needed 11.5 volts to your fixtures and ensure wire amperage capacities are not exceeded. Voltage drop is one of the biggest concerns when it comes to wiring low-voltage systems.
Before beginning any lighting project, you should predetermine which cable runs will feed which areas, the overall distance of these runs, total wattage on these runs and the gauge of the wire selected. The sequence of connecting one fixture to the other is also of utmost importance. You will also need a firm understanding of Ohms law (Volt x Amps = Watts) and how it works in relation to laying out the wiring for the lighting system. Without this, you can set yourself up to make a mistake that will not only place your system’s performance at risk, but also lead to a potentially dangerous situation. Let’s take a look at some different wiring techniques and the good and bad of each of them.
In the hub technique, a home run is brought from the transformer to a location within a cluster of fixtures. Two or more fixtures are then connected to this home run, usually via 25-foot lead wires on the fixtures. While this is often sold to new installers as an easy-to-install method, it results in decreased efficiency (higher electrical costs due to resistance created by small-gauge cable pre-attached to the fixtures) and the drain of your transformer’s power capacity. Another disadvantage is the “spiderweb” of wires this method can create, resulting in an increased chance of a service call due to a cut cable. To avoid making an additional wire splice, coiling up and burying extra cable is encouraged, which is costly, wasteful and unnecessary.
The T method is popular among seasoned installers for a variety of reasons. In this technique, a home run from the transformer is brought to the center fixture of a group that typically uses 12-gauge or larger wire. The run is connected in a “T” formation to a balanced number of fixtures on each side (usually no more than five lower-wattage fixtures). The use of 12 or 10-gauge main cable increases efficiency and allows you to either place greater loads on your home runs or to use a lower voltage tap, in effect giving you the ability to increase voltage to existing fixtures in the future or to add more fixtures to that run without having to install a new home run cable. This will make it less costly for future system expansion and may make the difference between your client agreeing to future work or not.
The key, as with other wiring methods, is to group fixtures in close proximity of one another so the variation in voltage is slight from one fixture to another. Your goal should be a less than .5-volt drop between fixtures throughout the system. This is entirely achievable when the proper techniques and transformers are chosen.
With this technique, the fixtures are chained together in a running series. This is the most common method used by the uneducated installer, and is usually the method used with low-dollar, box store kits. The problem with daisy chains is that it is usually taken to the extreme, and while you may have 12 volts at the first fixture, you can be left with less than half that at the end. The daisy chain can come in handy in certain instances in small zones if particular attention is paid to voltage drop.
Another method that is not recommended is the loop, or “lollipop,” which is basically a daisy chain with the wire run from the last fixture looped back to the first fixture or transformer tap. Polarity must be strictly maintained at each connection and at the transformer otherwise a dead short condition will result. Although this method is slightly better than the daisy chain, it still leaves a lot to be desired. This method makes it difficult or impractical to group fixtures based upon their load requirements. This setup is not commonly used and can lead to difficulties with troubleshooting and repair by technicians not involved with the original installation.
Structures and wiring
When wiring on or inside structures (especially wooden), it is imperative that local and national wiring codes are strictly abided by. The authors favor installing in-line fusing just before the first fixture for additional protection (or this can be installed at the common tap for that run). This can be accomplished with an automotive slow blow type fuse with a weatherproof enclosure. Test the amp draw on that cable run and install a fuse rated one step over that. For example, if your amp draw is 3.5, you use a 5-amp fuse. This is also helpful if you have especially long cable runs from the transformer and/or are using smaller gauge cable (not recommended).
Certain wiring situations (such as where cable passes through walls, under driveways, etc.—always consult National Electrical Code and local codes) may require power cable to be installed inside rigid or flexible protective piping or conduit. In areas or situations where it is not required, it may not be a bad idea to install power cable inside a sleeve or conduit to protect it from potential damage from future digging or rodents. Nobody likes to be called back for cut cables. At the very least, areas where cable is at a high risk for damage, such as seasonal flower beds, should be protected. Like they say, an ounce of protection is worth a pound of cure. Choosing the route in which your power cables will be placed is also a critical aspect of a successful wiring layout.
Are you properly connected?
When we are called out to service a job that we did not install, one of the biggest problems we see is poor connections. We have dug up things ranging from duct tape to pierce point connections. A good connection not only provides a secure bond of the conductors, but also provides a seal so that moisture will not wick into the wire jacket, causing corrosion and placing your connections at risk. Use a solid mechanical connector like an in-line barrel splice in conjunction with a direct burial sealant line shrink boot to cover the connections and seal the jacket. Another good method is to solder connections using a soldering pot and insert the soldered connection into a DRB tube filled with grease, making sure the wire jackets are submerged in grease.
Taking time to plan ahead and wire your system properly will help you on your way to building a high-quality system. You and your clients will appreciate the extra effort taken to do the job right the first time.
Billy Bradford owns and operates Integrity Outdoor Lighting in south Mississippi. Mike Gambino owns and operates Gambino Landscape Lighting in Simi Valley, Calif. Both contractors design and build high-end custom lighting systems.