Transformer & Voltage Drop
Size a low-voltage transformer and check voltage drop on a wire run before you dig.
1 · Transformer size
2 · Voltage drop on one run
Formula: drop = amps × (2 × length × ohms per 1,000 ft) ÷ 1,000, using a 12 V nominal load. Integrated LED fixtures often accept a wide range (for example 9–15 V); always check the spec sheet.
Why the 80% rule matters
Transformers last longest and run coolest below their rated capacity. Professionals size them so the connected load is no more than about 80% of the rating, which also leaves headroom to add fixtures later. In a Texas summer, when the transformer box can sit in full sun, that headroom matters even more.
Fixing voltage drop
Low-voltage systems lose voltage over long wire runs. Too much drop makes the far fixtures dim or flicker. The fixes are a higher transformer tap, heavier wire, shorter runs, or wiring methods like a hub or T split that feed fixtures from the middle. See the full transformer sizing guide, or let us diagnose an existing system.
More free tools
Questions about this tool
What size transformer do I need for 20 LED lights?
At 5 W each, 20 fixtures draw 100 W. Divided by 0.8 that is 125 W, so a 150 W transformer works, with a 200 W unit leaving room to grow.
Is 12 gauge wire enough?
12 AWG is the workhorse for most residential runs. Long runs or heavy loads may need 10 or 8 AWG to keep voltage in range.
Can I plug a transformer into any outdoor outlet?
It should be a weatherproof, GFCI-protected outlet. New outlets or circuits should be installed by a licensed electrician.
Tell us about your project
Share a few details and we will reach out to schedule a free consultation. We will talk through your goals, look at the property and, where it helps, show you a night demo before you decide anything.
- Custom design for your home, not a preset package
- Written proposal with fixture locations and pricing
- Warm, low-glare 12V LED systems built for Texas weather
- Final aiming visit after dark
Free consultation request
Ready to see your home in a new light?
Talk to Texas Landscape Lights about a custom lighting plan for your property, anywhere in Texas.
