FX Luminaire : The Lighting Professional's Choice
 
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Provide all fixtures with between 10.5-11.5 volts with all lamps installed and operating to maximize lamp performance and life. This is accomplished by:
 

Group fixtures into distance zones from the transformer - 0-40', 40-80' and 80-120'. Do not have a fixture that is 10' away from the transformer on the same cable run as a fixture that is 100' away. Try to center load your runs as much as possible to minimize the voltage differential between the first and last light (one volt difference is optimum, two volts is too much).

Run a separate cable run to each zone according to our Circuiting Guidelines.

By using the PotenzaX and a VoltMeter you can then select the transformer voltage tap (12, 13 or 14v) that provides each fixture about 10.5 - 11.5 volts.
 
 

Note: All the lights can be in the 40-80' zone but you still need to run several separate cable runs to reduce the load per cable, thereby minimizing voltage loss. Typically a 300-watt transformer has three separate cable runs with about 80 to 120 watts on each cable - a 600-watt transformer has about five separate cable runs, again, with about 80 to 120 watts on each cable. For ease of installation you can drop a couple of cables out of the transformer into a subterranean drip irrigation 6-8" round valve box where the five field cables can be spliced to the couple of transformer cables. This is a easier connection to make because it is difficult to cram 5 cables into the bottom of the transformer.

SUMMARY
For maximum light output and lamp life, the goal in low voltage systems is to provide each lamp with between 10.5 - 11.5 volts. To stay within this 1 volt optimum differential you must group the fixtures into distance zones from the transformer as shown above and not overload the cable with excessive wattage. Using the PotenzaX you can then select the voltage tap that will provide no more than 11.5 volts at the first lamp. If you have grouped the fixtures according to the above graphic then the last light will have around 10.5 volts. When it's possible, center feed the zone as this will provide a much more even voltage to each fixture.