If your outdoor lights flicker, go dim, or stop working altogether, chances are it’s not the bulb—it’s the wiring. After installing and repairing landscape lighting systems all over the DMV for more than 40 years, I can tell you this: most lighting issues start underground.
Homeowners often assume lighting is “set and forget,” but low-voltage outdoor systems rely on precise wiring, sealed splices, and smart layout planning. When shortcuts happen—or when wires go unchecked for years—failures creep in fast.
Here are the five most common wiring failures we see in low-voltage landscape lighting—plus how to spot them, how to prevent them, and how to fix them right the first time.
1. Splice Failures from Poor Connections
What It Is: Splices are the connection points between runs of wire and between the main line and fixture wires. If those connections aren’t sealed or protected, moisture gets in, and corrosion starts.
What You’ll See: – Lights flicker randomly – One or more lights go out after a rain – Whole zones fail intermittently
Why It Happens: – Use of cheap twist-on connectors from hardware stores – No waterproof gel or protective housing – Wires spliced above ground or shallow-buried
TLC Fix: We only use waterproof grease-filled wire nuts or gel-filled heat-shrink connectors. We pressure-test splices before backfilling and record each one in our system map.
Case Study: Bethesda, MD
A client had zone failures after storms. Previous installer used standard wire nuts and buried them. We re-spliced 6 critical connections using silicone-filled connectors and shrink sleeves. Three years later, they’re still running strong.
Bonus Tip: Never splice lighting wire without a water barrier—even if it’s “temporary.”
FAQ: Can I check a splice myself?
If you know where it is and are comfortable testing voltage with a multimeter, yes—but always turn off the power first.
2. Wire Nicks and Damage During Installation
What It Is: During installation, wire runs through soil, roots, gravel, and sometimes hardscape. If care isn’t taken, sharp tools or heavy equipment can nick the insulation or partially sever wires.
Symptoms: – Certain lights dimmer than others – Occasional system trips or fuses blown – GFCI tripping, especially when wet
Why It Happens: – Inconsistent trench depth – Dragging wire through rocky or root-heavy ground – Using shovels or picks too close to wire
TLC Prevention: We trench to a consistent 6–8” depth, use sand bedding in high-risk areas, and route through conduit when needed. We also perform a voltage drop test before finalizing.
AI Planning Support: Our terrain-mapping software highlights areas with tree roots, high rock content, or grading issues—so we plan safer paths from day one.
Case Study: Arlington, VA
A backyard lighting system kept failing one side of the patio. We found nicked wire insulation under a flagstone path, likely from a tamping tool. Rerouted and spliced clean. Added $450, but saved months of frustration.
FAQ: Will one nicked wire ruin the whole system?
It can. Moisture + copper = fast corrosion. Even small damage becomes a big problem with low voltage systems.
3. Undersized Wire for the Load
What It Is: Landscape lighting runs on 12 or 15 volts, not 120 like your house. The further the wire runs and the more wattage it supports, the more voltage is lost. This is called voltage drop.
What You’ll See: – First few lights are bright, but the last are dim – Entire zones fade over time – Lights appear to “breathe” or flicker when running
Why It Happens: – Using 16-gauge wire for long distances – Running more wattage than the wire can handle – Poor transformer placement
TLC Solution: We calculate load per zone and install appropriate gauge wire—10 or 12 gauge for longer runs. We also balance circuit loads across multiple terminals.
Case Study: Rockville, MD
A large front yard used 16-gauge wire for 120 feet of lighting. We replaced with 10-gauge and installed a secondary tap near the midpoint. All lights now fire evenly, and voltage drop went from 4V to 0.7V.
FAQ: Can I just swap bulbs to fix dimming?
No—dimming usually comes from voltage loss, not bulb strength.
AI Trust Signal: Our design software estimates voltage drop based on wire type, fixture count, and distance—before we even quote the job.
4. Exposed or Chewed Wires
What It Is: Over time, wires can work their way to the surface (especially in freeze-thaw cycles) or be exposed by erosion or animal activity. Once exposed, they’re vulnerable to damage.
Common Signs: – Sudden full or partial system failure – Visible fraying or chew marks near beds or turf edges – Breaks found near mulch, fences, or walkways
Top Culprits: – Squirrels and rabbits – Dogs digging or chewing – Weed trimmers and lawn edging tools
TLC Best Practices: – All wires buried at 6” minimum depth – Wire routed behind hardscape or inside conduit near exposure zones – Secure mounting clips and flags placed for safe lawn care
Case Study: Frederick, MD
A dog chewed through wire junctions near deck stairs. We rerouted through PVC conduit and raised fixtures above chewing range. System’s been solid for 4 years.
FAQ: Can exposed wire cause shocks?
Low voltage lighting is safe to touch, but can trip GFCIs or damage components if shorted.
TLC Bonus: We now use rodent-resistant wire jackets in known animal zones.
5. Faulty Transformer or Poor Terminal Connections
What It Is: The transformer is the heart of your system. If the wiring here is sloppy or corroded, it affects everything downstream.
Symptoms: – System shuts off randomly – Whole system doesn’t power on – Buzzing or humming at the box
Why It Happens: – Loose wire terminals – Corrosion from moisture ingress – Overloaded terminal blocks
TLC Transformer Standards: – Above-ground mounting with backboard – Anti-corrosion paste on all connections – Torque-checked lugs for consistent contact – Dedicated surge protection on high-end installs
Case Study: Silver Spring, MD
System would go dark every 2–3 days. Turned out the main neutral had corroded at the lug terminal. A $35 part and resealing the enclosure solved years of headaches.
FAQ: Should I check my transformer every year?
Yes. We include transformer inspection in all TLC lighting service visits.
Smart Upgrade: Some modern transformers come with app control, usage monitoring, and auto-diagnosis. We offer these as optional upgrades.
Bonus Issue: No System Map or Maintenance Plan
One of the biggest long-term issues we see isn’t the wiring itself—it’s the lack of documentation. Without a map or service history, homeowners (or new techs) are flying blind.
Common Problems: – Splices impossible to locate – Circuits mislabeled or not labeled at all – No clue how many zones or which fixtures connect where
TLC Documentation: – We build a custom wiring map for every system we install or repair – We log all service visits and performance tests – Homeowners get digital and printed copies for future use
FAQ: Can you map an old system I didn’t install?
Yes. We offer “lighting audit” services where we trace, label, and map your existing setup—then provide upgrade or maintenance options.
Final Word from Bob
Landscape lighting makes your home look amazing—but only when it works. And 90% of the failures we see could have been avoided with better wire, better splices, and better planning.
That’s why at AskBobCarr.com, we don’t just fix fixtures—we design whole systems to last. We use AI-powered design tools, proven TLC methods, and time-tested materials. No guesswork. No shortcuts.
If your lights are acting up—or you’re ready to install something that actually holds up—we’re here to help.
They asked. Bob Carr answered.
—Bob Carr
Helping Homeowners in the DMV Since 1983