To wire 12V LEDs in parallel, you must connect the positive (red) and negative (black) leads of every LED strip or puck directly to the corresponding V+ and V- terminals of a constant-voltage DC power supply. This "home-run" or "star" topology ensures each fixture receives the full 12V, preventing the severe voltage drop and dimming that occurs when strips are daisy-chained end-to-end. For a standard under-cabinet or cove lighting setup drawing under 12.5 amps, use 14 AWG stranded wire for the main DC trunk and 18 AWG for the individual branch runs.

The Decision Path: Topology and Component Selection

Before stripping any wire, you must determine whether your specific LED hardware requires a series or parallel circuit, and select the correct driver. Wiring raw, unresisted 5mm LEDs in parallel directly to a voltage source will cause thermal runaway and destroy the diodes. However, commercially available 12V and 24V LED strips and pucks have built-in current-limiting resistors or constant-current ICs, making them designed specifically for parallel wiring.

LED Hardware Type Required Topology Power Supply Type Verdict & Action
Raw 5mm / 10mm LEDs Series (with resistor) or Parallel (with individual resistors per LED) Constant Current Driver or DC Bench Supply Avoid for home lighting. Use pre-assembled modules instead.
12V LED Strips / Pucks Parallel (Home-Run / Star Wiring) 12V Constant Voltage (CV) DEFAULT PICK: Use Mean Well LRS-150-12 (150W, 12.5A max).
24V LED Strips Parallel (Home-Run / Star Wiring) 24V Constant Voltage (CV) Choose for runs over 20ft to minimize voltage drop.
Concrete Recommendation: For standard 12V home lighting projects (up to four 16-foot strips), terminate your decision path here: Purchase the Mean Well LRS-150-12 enclosed power supply. It provides 150 watts of clean, regulated 12V DC, features built-in short-circuit protection, and its screw-terminal block makes parallel home-run wiring significantly more reliable than cheap plastic "brick" adapters.

Tools, Materials, and Wire Sizing

Sizing your wire correctly is critical. Low-voltage DC circuits carry high amperage compared to their AC counterparts. A 150W load at 120V AC draws only 1.25A, but that same 150W load at 12V DC draws 12.5A. Undersized DC wire will overheat and cause unacceptable voltage drop.

Materials List

  • Power Supply: Mean Well LRS-150-12 (12V DC, 12.5A output).
  • AC Feed Wire: 14/2 NM-B (Romex) with ground, rated for 15A circuits.
  • DC Main Trunk Wire: 14 AWG stranded copper (Red and Black). Rated for 15A.
  • DC Branch Wire: 18 AWG stranded copper (Red and Black). Rated for up to 5A per branch.
  • Connectors: Wago 221 Series Lever Nuts (2-port and 3-port) for in-line DC splicing.
  • AC Junction Box: Steel or PVC 4x4 junction box with cable clamps for the mains transition.

Tool List

  • CAT III or CAT IV Digital Multimeter (for verifying dead circuits and DC output).
  • Wire strippers (capable of handling 14 AWG to 18 AWG solid and stranded).
  • Non-contact voltage tester (NCVT).
  • Insulated screwdriver set.
NEC Code Caveat (Class 1 vs. Class 2): Under NEC Article 725, a 150W 12V power supply exceeds the 60W/5A limit for Class 2 circuits. This means your low-voltage DC wiring is legally classified as Class 1. If you are running these DC wires inside your walls, you must use CL2/CL3 rated cable or run standard NM-B in conduit, and the wires must be routed with proper separation from other line-voltage circuits. For surface-mounted under-cabinet runs, standard stranded wire is acceptable.

Mains Safety & AC Power Supply Wiring

The Mean Well LRS-150-12 requires a hardwired 120V AC connection. This involves lethal mains voltage. If you are not comfortable working inside a junction box, hire a licensed electrician to run the AC feed and leave you a blank junction box to connect your driver.

CRITICAL SAFETY PROCEDURE:
  1. De-energize: Turn off the 15A or 20A breaker supplying the lighting circuit at the main panel.
  2. Lock/Tag: Place a padlock or warning tag on the breaker panel to prevent accidental re-energizing.
  3. Verify Dead: Use a non-contact voltage tester (NCVT) on the wires, then confirm with a CAT III multimeter set to AC Volts. Measure Hot-to-Neutral, Hot-to-Ground, and Neutral-to-Ground. All readings must be 0.0V before proceeding.

AC Termination Steps

  1. Route the 14/2 NM-B cable into the 4x4 junction box and secure it with a Romex clamp.
  2. Strip 3/4 inch of insulation from the black (hot), white (neutral), and bare (ground) wires.
  3. Connect the Bare/Green ground wire to the green grounding screw inside the steel junction box, and pigtail a second ground wire to the Earth Ground (⏚) terminal on the Mean Well power supply.
  4. Connect the White neutral wire to the N terminal on the power supply using a wire nut or Wago lever nut.
  5. Connect the Black hot wire to the L (Line) terminal on the power supply.
  6. Secure the power supply inside an enclosed metal housing or mount it to a backboard ensuring the ventilation louvers are not obstructed.

Step-by-Step: Wiring the 12V DC Parallel Branches

True parallel wiring in LED lighting is often called "home-run" or "star" wiring. Instead of plugging Strip B into the end of Strip A (which forces the copper traces of Strip A to carry the combined amperage of both strips, causing severe voltage drop), you run individual branch wires from a central distribution point back to each strip.

  1. Prepare the DC Main Trunk: Cut a length of 14 AWG Red and 14 AWG Black stranded wire long enough to reach from the power supply to your first central distribution point (e.g., inside a cabinet).
  2. Terminate at the Driver: Loosen the screws on the DC output side of the Mean Well driver. Insert the 14 AWG Red wire into the V+ terminal and tighten securely. Insert the 14 AWG Black wire into the V- terminal and tighten. Give the wires a firm tug to ensure a solid mechanical bond.
  3. Create the Parallel Distribution Node: At the end of your 14 AWG main trunk, use Wago 221-613 (3-port) lever nuts to split the circuit. Strip 11mm of insulation from your 14 AWG trunk and your 18 AWG branch wires.
    • Insert the 14 AWG Red trunk wire and up to two 18 AWG Red branch wires into one red Wago 221 lever nut.
    • Insert the 14 AWG Black trunk wire and up to two 18 AWG Black branch wires into a black Wago 221 lever nut.
  4. Run the Branches: Route the 18 AWG Red and Black branch pairs to your individual LED strips or puck lights. Keep branch runs under 15 feet to maintain acceptable voltage drop.
  5. Terminate at the LED Fixtures: At each LED strip, solder the 18 AWG Red wire to the strip's +12V copper pad and the 18 AWG Black wire to the GND pad. If using quick-connectors, ensure the Red wire aligns with the strip's positive arrow indicator.
  6. Daisy-Chain Expansion (If Necessary): If you have more than two strips, run another pair of 14 AWG wires from the remaining port on your first Wago nuts to a second set of Wago nuts further down the cabinet, repeating the branch split. This maintains the parallel home-run architecture.
Voltage Drop Math for 18 AWG Branches: 18 AWG copper has a resistance of roughly 6.38 ohms per 1,000 feet. If your 18 AWG branch run is 10 feet long (20 feet round-trip) and your LED strip draws 3 Amps, the voltage drop is calculated as: V_drop = 3A × (6.38 × 20/1000) = 0.38V. Your strip will receive 11.62V, which is well within the acceptable operating range for 12V LEDs.

Verify, Test, and Troubleshoot

Never energize a newly wired circuit without a verification sequence. Grab your multimeter and follow these steps before flipping the breaker.

Pre-Flight Checks

  • Visually inspect the AC junction box. Ensure no bare copper is exposed outside the wire nuts or Wago connectors.
  • Verify the DC V+ and V- wires are not touching each other or the metal chassis of the power supply.
  • Ensure the Mean Well driver's internal cooling fan (if equipped on higher wattage models) is unobstructed.

Energize and Measure

  1. Remove the lock/tag and turn the 15A AC breaker back on.
  2. Set your multimeter to DC Volts.
  3. Place the red probe on the V+ screw terminal and the black probe on the V- screw terminal at the power supply. Expected Reading: 12.0V to 12.2V. (If it reads 0V, check the AC breaker and the internal fuse of the driver).
  4. Move to the furthest LED strip in your parallel run. Pierce the wire insulation or touch the probe to the solder pads. Expected Reading: >11.4V. If it reads below 11.0V, your branch wires are too long or too thin, and the LEDs at the end of the strip will appear visibly dimmer or shift color (in RGB strips).

The Most Common Botch: Pseudo-Parallel Daisy Chaining

The most frequent mistake DIYers make is assuming that plugging the female connector of Strip B into the male connector of Strip A constitutes "parallel" wiring because both strips are on the same circuit. Electrically, the copper PCB traces on Strip A are now acting as a series resistor carrying the combined load of both strips.

Symptom: Strip A glows brightly, but the far end of Strip B is dim, flickering, or shows a color shift (e.g., white light turning pink because the blue diodes require higher forward voltage and drop out first).

The Fix: Cut the connector off Strip B. Run a dedicated 18 AWG Red/Black pair from your central Wago distribution node directly to the input pads of Strip B. True parallel wiring requires every fixture to have its own dedicated path back to the power source. For a deeper understanding of why series resistance ruins low-voltage lighting runs, review the fundamentals of series and parallel circuit theory.

By sticking to a strict home-run topology, using 14 AWG for your main trunk, and terminating with lever nuts instead of twist-on connectors, your 12V LED installation will deliver uniform brightness and operate safely for the lifespan of the diodes.