Voltage Drop – How to install landscape lighting
Voltage drop is the decrease in electrical current experienced as electricity travels through a wire. This is most commonly seen as dim light output from your landscape lights. Voltage drop is especially noticeable when many lights are wired in series. You will be able to see the brightness decrease as the lights get further from the transformer.
In landscape lighting voltage drop is affected by:
- distance of the wire run
- amount of wattage on the run
- spacing of fixtures
- output from the transformer
- size of the low voltage wire
- quality and placement of connections
In most installations a few simple tips will help you avoid voltage drop issues.
Group lights into zones – to prevent voltage drop. Each zone gets its own wire going directly back into the transformer.
Zone Wattage – Keep wattage on each zone under 150 watts.
- 12/2 low voltage wire = 100 watts
- 10/2 low voltage wire = 150 watts
Zone Spacing – try to keep all lights in a zone fairly close together. For example you wouldn’t want a light a few feet away from the transformer on the same zone as a light 100 feet down the line.
|Connecting all of your lights in a straight line sometimes called a “series” or “daisy chain” creates voltage drop.|
|Run the wire from your transformer to the center of the zone and split the wire with a “T” connection.|
|Making a “T” connection reduces light output variations between the first light on the run and the last light.|
Choose a Professional low voltage transformer with multiple voltage taps – to prevent voltage drop.
On long wire runs the voltage coming form the transformer needs to be increased to reduce voltage drop. Our multi-tap Kichler transformers have 12 volt, 13 volt, 14 volt and 15 volt terminals. Testing the voltage at each light is best way to determine what voltage terminal to use.
The goal when designing a low voltage landscape lighting system is to have the voltage at each fixture between 10.8 volts and 11.8 volts. This ensures powerful and even light output from each fixture without degrading lamp life.
Use a volt meter to measure voltage at each fixture. If voltage is less than 10.5 volts the light will look dim and yellowish. If voltage is above 12 volts the lamp life will be decreased without much benefit to light output.
Choose the voltage terminal in the transformer for each zone that puts all of your lights between 10.8 volts and 11.8 volts.
Use a larger sizelow voltage wire – to prevent voltage drop.
We recommend using 10/2 low voltage wire for all wire runs longer than 50 feet in halogen systems. The larger 10/2 wire will help reduce voltage drop. 12/2 low voltage wire is ok for shorter runs and great for Kichler LED landscape lighting fixtures.
Kichler LED landscape lights come on at the same brightness between 9 volts and 15 volts. So voltage drop is a non issue in most landscape lighting systems using Kichler LEDs.
It is always a good idea to stay away from long runs of smaller 14/2, 16/2 & 18/2 wire. Many of the landscape lighting kits available at the home stores include 16/2 wire. This smaller wire creates voltage drop and is unsafe. Short circuits or cuts in smaller wires are less likely to trip the breaker in the transformer. This could pose an overheating risk to your system components.
Make proper connections – to prevent voltage drop.
When stripping insulation away from low voltage wire sometimes strands of copper will get cut and removed with the plastic insulator. Be very careful to minimize the copper removed. We want as much copper contact as possible at the connection.
We recommend using a dry wire nut connection and then drop the wire nut into a waterproof splice tube. Twist the wire nut very tight and check all of the wire to make sure they aren’t loose. This type of connection allows the copper strands to make solid contact.
The gel filled blue wire nuts available at the home stores do not make a tight connection and are not recommended.
The tips above will help you avoid voltage drop in most installations. For long wire runs 200 feet plus check out the voltage drop equation.
Check out the Voltage Drop Equation.