ACCESSORIES: LOW VOLTAGE CABLE & TRANSFORMERS
1080
LUMIERE®
COOPER LIGHTING
`
DESCRIPTION
Transformers reduce line voltage to 12 volts for use with Lumière low voltage fixtures.
ORDERING INFORMATION
SAMPLE NUMBER: TR900T
Order transformers and low voltage cable as separate line items.
Transformer Selection
The total wattage of all lamps used must not exceed the rating of the
transformer selected for the installation. For example, a 150VA (VA = watts)
transformer cannot power four fixtures with 50 watt lamps.
The transformer selected should match the total lamp wattage as
closely as possible. It is good practice to use at least 33 to 50 percent,
and no more than 85 to 90 percent, of the transformer’s rated capacity.
Make sure that the transformer selected reduces the appropriate line
voltage. For example, do not use a 120 to 12 volt transformer with a
277 volt system. Lumière Atlantis series fixtures (model 1407 - 1409)
must be used with model T300, which is approved for use in pool
and spa type applications.
Transformers must be installed in accordance with local and national
electrical codes and other rules, regulations and requirements.
Voltage Drop
Resistance to electricity passing through electrical wiring causes the
voltage at the end of a run of wire to be lower than the voltage at the
transformer. This will cause fixtures at the end of a run to be noticeably
dimmer than those closer to the transformer.
The factors affecting voltage drop are the total wattage of lamps on the
run, the length of the run and the gauge of the wire.
There are several ways to minimize the impact of voltage drop:
• Use larger gauge cable
• Shorten cable runs
• Use lower wattage lamps
• Reduce the number of fixtures on the run
• Divide the fixtures over more runs from the transformer
• Use multiple transformers
Voltage drop is not always bad.
For example, dropping voltage at the lamp to 11.5 volts will give
80% of the lamp
'
s rated candlepower, and double the rated life of
the lamp. This is acceptable in most applications, and will result in
lower maintenance costs.
The accompanying chart demonstrates how voltage at the lamp
affects rated lamp life and rated candlepower:
Sample Landscape Lighting Installation
We recommend using 12/2 or larger inground stranded cable. To control
voltage drop, for each 100 watts allowed, use 100 feet of wire, maximum,
to stay at approximately 10 volts at the end of the run. For example, a 300
watt (300VA) transformer may have three separate runs with 100'
maximum on each run. This is standard procedure for low voltage
installations. Any setup within these parameters will maintain sufficient
lumen output. (Provided as an example only — output requirements
may vary depending on individual situations and preferences.)
VOLTAGE DROP FORMULA
Transformers are available in four basic types:
• Hard wire installation –
Standard outdoor low voltage lighting transformer for hard wiring direct to conduit.
• Cord and plug –
Plug in directly to existing outlets, for ease of installation. Also available with a built in timer.
• Inground –
Low profile inground installation for reduced visual impact and increased flexibility.
• Compact solid state electronic transformers –
For use in approved housings or boxes.
Total watts on cable x length of run
Cable size constant*
= Voltage Drop
CABLE SIZE CONSTANT CHART*
Cable size #18 #16 #14 #12 #10 #8 #6
Cable constant 1380 2200 3500 7500 11,920 18,960 30,150
VOLTAGE DROP CHART
Voltage at lamp
13.2
12.6
12.0
11.5
11.0
10.5
10.0
Life expectancy of lamp
2/3 rated life
3/4 rated life
as rated
2X rated life
3X rated life
5X rated life
9X rated life
% of rated candlepower
350
180
100
80
74
65
50
