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How To Wire Outdoor Low Voltage Lighting - Part 2

Part 1 Part 3

Therefore the method you use to wire your outdoor low voltage lighting system can make the difference between a successful and unsuccessful home improvement project.

The most common method of installation of an outdoor low voltage lighting system has a transformer, possibly with options such as photo cells and timers, mounted on the wall of the home. The transformer has an input of 120VAC and then a cable, with 2 wires, runs from the transformer to the first light fixture, then to the second light fixture and so on, as shown in Figure 3.

outdoor low voltage wiring diagram 1

Figure 3 - Low voltage wiring diagram 1

The second lamp in the circuit will have reduced voltage, and hence less light output than the first lamp in the circuit. This is because it is receiving less voltage due to the additional length of wire between the first and second lamp. The third lamp in the circuit will have less voltage than the second lamp, and hence less light output than the first or second lamp in the circuit, and so on.

This does not make for attractive landscape lighting.

There are a few things that can be done to reduce the voltage drop to the light fixtures and make all of the lamps have similar light output.

  1. You can increase the wire gauge so that the voltage drop from the transformer to the first and subsequent light fixtures is minimal. See Table 1.
  2. Note: There is a design limit to the total amount of watts that any specific wire gauge can handle. Table 2 provides the total wattage over defined distances relative to wire gauges. It is important to keep this information in mind when designing the wiring of your outdoor low voltage lighting system.

Table 2
Maximum Wattage For Wire Gauges
Wire gauge Maximum Watts
16 155
14 215
12 250
10 360

 

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  1. You can wire your light fixtures in a loop, as shown in Figure 4. This basically balances the first and last lamp in the outdoor lighting circuit. Light fixtures in the middle will still have a lower voltage than the first and last fixture. However, depending on actual wire lengths the difference may not be noticeable.

outdoor low voltage wiring diagram 2

Figure 4 - Low voltage wiring diagram 2

  1. You can use larger gauge wire for the main run and use smaller gauge wire to “T” off from the main run to the individual light fixtures, as shown in Figure 5.

using different size wires

Figure 5 - Using different size wires

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