LX - Running Cable to Lighting Fixtures

Tabs

Read Article

Once the transformer has been installed and all fixture locations determined, the next step is to run the correct size cable from the transformer to the fixtures while providing each fixture with proper voltage range. LED fixtures should be provided between 10 and 15 volts AC. With incandescent fixtures the voltage range at fixture should be between 10.5-11.5 volts AC. This is accomplished by:

Grouping fixtures into distance zones as illustrated below. Do not have a fixture that is 10' away from the transformer on the same cable run as one that is 100' away.
Use the proper cabling method for the application. For incandescent fixtures, try to center load all cable runs when possible to minimize the voltage differential between fixtures. Maximum voltage differential between the first fixture and the last fixture on any given circuit should not exceed 1 volt with a 0.5 volt differential being optimum.
LED fixtures can vary in voltage and will all have the same brightness as long as between 10 and 15 volts is being supplied to each fixture.
Use the correct size cable to accommodate voltage drop. As a general rule of thumb, limit the wattage load per each cable run to no more than 100 to 160 watts.

Wattages shown are per 12 gauge cable. Install additional cable runs as needed to complete project. To increase wattage maximum, run 8 gauge or double 12 gauge to the first fixture in the zone. Use a digital voltmeter to fine tune circuits.

Installation

Cabling Methods

Within each cabling zone, you may utilize any of a number of cabling methods. The primary objective is to minimize voltage drop by installing the proper size feeder cable (home run) to each zone and to make sure that each fixture on each cable run is receiving between 10.5 and 11.5 volts, or 10–15 volts for LED fixtures. Center feeding the “home run” (the main cable run from the transformer to the first fixture on the circuit) will help minimize the voltage differential between the first fixture and the last fixture on the cable run.

Daisy chain method (Recommended for LED systems)

Daisy chained circuits are the least efficient cabling method as more voltage is fed to the first fixture on the run and due to voltage drop, each subsequent fixture receives less and less voltage. This is not a problem for FX LED fixtures due to its large voltage acceptance range of 10–15 volts.

Tee (or Center Load) method (Recommended for Incandescent systems)

The tee method center feeds the “home run” section of the cable and reduces the voltage differential between the first fixture and the last fixture on either side of the “tee.” This method is the preferred circuiting technique as it is easy to install and minimizes the voltage drop between first and last fixtures.

Connecting Cables to Terminal Block

TRANSFORMER TERMINAL BLOCK

The LX Series Transformer includes one “common” lug, and three “hot” lugs. Four smaller lugs are located on left side of the voltage lugs, which provide a connection for an External Transformer Signal of 12-24 volts and two connections for the proprietary low voltage Photocell unit.

COMMON LUGS

One conductor from each cable run coming from the lights to the transformer must be connected to one of the common lugs. The other conductor will be installed into the hot lug that provides the optimum voltage for each circuit.

CHOOSING THE PROPER “HOT” VOLTAGE LUG

Choosing the proper “hot” voltage lug in which to install the conductor is determined by the circuit’s voltage drop. If a circuit’s voltage drop is calculated to be about 3 volts, install the “hot” side of the cable into the 14 volt tap to assure proper voltage at the lamp (14 volts minus 3 volts = 11 volts). The voltage reading at each “hot” lug will vary depending upon the incoming voltage provided by the 120 volt receptacle. If the receptacle reads 128 volts, it is not uncommon for the 12 volt lug on the transformer to read 12.6–12.9 volts. On the other hand, if the receptacle is reading only 116 volts, the 12 volt lug may only read 11.8–12.2 volts. Always verify both high voltage and low voltage readings with a digital voltmeter. Fine-tune each circuit by using a digital voltmeter. Lamps perform best when supplied between 10.5 and 11.5 volts. Before waterproofing wire connections, take a voltage reading at the first and last fixture on each circuit. If the voltage reading at the first fixture on the circuit reads less than 10.5 volts, move the conductor up to a lug that will provide approximately 11 to 11.5 volts. LED fixtures should be provided between 10 and 15 volts.

Note: See all voltage drop charts below.