Create a Landscape Lighting Plan

Create a plan for your landscape lighting installation by sketching out the area and marking the desired location and style (spot, path, washer etc.) of each light fixture. Create a list of wattages for the light fixtures you will use.

Wire cost and installation labor can be reduced by following a few simple guidelines: - Create groups of light fixtures. Each group is connected to the transformer by one “run” of wire. - Piggyback a distant light fixture onto the end of a group closer to the transformer to save wire, but this may require an increased wire gauge. - Take care to not put too many halogen light fixtures on a single run.

These guidelines will assist you in designing a wire layout that keeps each run as short as possible. This reduces the amount of large gauge wire required and improves the installation by limiting voltage drop.


Determine the best place to locate your transformer using these guidelines:

  • Location is centralized to the light fixtures.
  • Location has available a dedicated 110/120VAC outlet or one can be easily added.
  • Location minimizes long distances.
  • Location avoids running power lines under walkways or driveways.

Add the transformer location to your plan.

Plan Ahead

When installing any light fixture, it is wise to add a “service loop” in the wire. This is simply a 12” to 24” length of wire coiled at the base of each fixture. This comes in handy if a light fixture requires service or needs to be relocated due to maturing landscaping.

Design Wire Layout

Using the guidelines above, draw power lines on your sketch, experimenting with different methods of connecting all of the light fixtures. Once you are satisfied with your wire layout, it’s time for some legwork.

For each run, measure the length of wire needed to connect from the transformer to each light fixture, and calculate the total wattage of the light fixtures. Write it all down on your plan.

Calculate Wire Gauge Per Run

Use the Minimum Wire Gauge tool. For each run, enter the Total Wattage, the Total Length, and check the Voltage Tap field (you should use a 15V tap on the transformer for LED and a XXV tap for halogen). Press Calculate. The app returns the minimum wire gauge that is appropriate for the run. If the minimum wire gauge is barely sufficient to power the run, the app will also recommend the next larger gauge for future expansion. Write down the wire gauge for each run.

Calculate Transformer Size

Now use the Minimum Transformer tool to calculate the total wattage including voltage loss over the wire. You will enter and calculate each run in succession. DO NOT use the Reset button between runs. For each run, enter the Total Wattage, Total Length, Voltage Tap and the Wire Gauge calculated earlier. Click Calculate.

In the Answer section there will be several new bits of data. The Minimum Transformer tool first tests the run to make sure the wire gauge used in the calculation is safe and displays a response in the “Check Run” field. If that passes the “Total Runs Calculated” field will increment to 1. Then the tools displays the current total wattage including voltage loss and recommends a transformer size.  

Enter the next run by typing over the previous information and click Calculate again. The “Total Runs Calculated” will increment to 2 and the new total wattage will be displayed.

Repeat until you have entered all runs. When you finish, the tool should show the same number of runs calculated as you have on your plan. And finally, you have the last piece of the puzzle, the minimum transformer you can use for your landscape lighting project. The tool may recommend a larger transformer. This is because, as your landscape matures it is likely that you will need additional light fixtures or to replace some with higher outputs.

Always adhere to local and National Electric Code regulations.