LED Strip Wiring Guide
Calculate the current draw, choose the right wire gauge and select the correct fuse for any 12V or 24V LED strip installation. Covers van builds, shed lighting, workshop strips and under-cabinet installs — with a worked example for a 5 m strip run.
Last updated: May 2026
The scenario
You want to install 5 m of 12V LED strip lighting in a camper van, workshop or shed. The strip is rated at 14.4 W/m (a common value for mid-brightness COB or SMD5050 strips). You need to know the total current, what wire to use for the run from the power supply to the strip, and which fuse to fit to protect the wire.
Step 1: Calculate total power and current
Multiply the strip's watt-per-metre rating by the total strip length to get total power. Divide by the supply voltage to get current in amps.
Power = 14.4 W/m × 5 m = 72 W | Current = 72 W ÷ 12 V = 6 A
Common LED strip watt ratings and their currents at 12V and 24V:
| Strip rating (W/m) | 5 m at 12V (A) | 5 m at 24V (A) | Typical type |
|---|---|---|---|
| 4.8 W/m | 2.0 A | 1.0 A | Low-brightness SMD3528 |
| 9.6 W/m | 4.0 A | 2.0 A | Mid SMD5050 RGB |
| 14.4 W/m | 6.0 A | 3.0 A | High SMD5050, COB single colour |
| 24 W/m | 10.0 A | 5.0 A | High-density COB, trade strip |
Use the calculator: Enter total power (W) and supply voltage into the Watts / Volts / Amps Calculator to confirm current, or use it in reverse if you know the current and voltage.
Step 2: Choose wire gauge for the run
Wire gauge depends on the current and the length of the run from the power supply or battery to the strip. For LED strips, keep the voltage drop under 3% of the supply voltage — otherwise strips at the far end will be dimmer than at the start.
For 12V: 3% of 12V = 0.36V drop allowed. For 24V: 3% of 24V = 0.72V allowed. 24V strips are more tolerant of long runs because the absolute voltage loss is less significant.
| Current (A) | Run to strip (m) | 12V recommended wire | 24V recommended wire |
|---|---|---|---|
| 2 A | up to 8 m | 0.75 mm² (AWG 18) | 0.5 mm² (AWG 20) |
| 4 A | up to 5 m | 1.5 mm² (AWG 15) | 0.75 mm² (AWG 18) |
| 6 A | up to 3 m | 1.5 mm² (AWG 15) | 1.0 mm² (AWG 17) |
| 6 A | 3 to 6 m | 2.5 mm² (AWG 13) | 1.5 mm² (AWG 15) |
| 10 A | up to 3 m | 2.5 mm² (AWG 13) | 1.5 mm² (AWG 15) |
Use the calculator: Enter your current, one-way run length, supply voltage (12 or 24), copper wire and 3% drop limit into the Wire Gauge Calculator. The result shows the minimum wire size and the actual voltage drop in volts and percent.
Step 3: Select the fuse
Fit a fuse rated at 125% of the strip's normal current, then round up to the next standard blade fuse or in-line fuse size. The fuse protects the wire, not the strip — a fuse rated too high will not blow before the wire overheats.
| Strip current (A) | 125% value | Fuse to use |
|---|---|---|
| 2 A | 2.5 A | 3 A |
| 4 A | 5.0 A | 5 A |
| 6 A | 7.5 A | 7.5 A (or 8 A) |
| 10 A | 12.5 A | 15 A |
Place the fuse as close to the power supply or battery terminal as possible — ideally within 15 cm of the positive output. An in-line blade fuse holder is standard for LED strip wiring.
Use the calculator: Enter the circuit's normal current into the Fuse / Breaker Sizing Calculator to confirm rating.
Step 4: Choose and size the power supply (if mains-powered)
If you are running from a 230V mains outlet rather than a 12V battery, you need a DC power supply (PSU) or LED driver. Size it for at least 120% of the strip's total power to avoid running at full load continuously, which reduces PSU lifespan.
Minimum PSU power = 72 W × 1.20 = 86.4 W → choose a 100 W PSU
| Total strip power (W) | Minimum PSU (W) | Standard PSU to buy |
|---|---|---|
| 24 W | 29 W | 30 W or 60 W |
| 48 W | 58 W | 60 W |
| 72 W | 86 W | 100 W |
| 120 W | 144 W | 150 W or 200 W |
For dimmer compatibility: most LED strips work with PWM dimmers placed between the PSU and the strip. The PWM dimmer must be rated for the full current of the strip, not just the dimmed current.
Common mistakes
- Undersizing the wire for long runs: using 0.75 mm² for a 6 A strip on a 5 m run causes a 1.5 V drop at the strip end — the last metre will be noticeably dimmer. Use 2.5 mm² for that run.
- No fuse on a direct battery connection: in a van build, any positive wire from the battery without a fuse is a fire hazard. Fit a fuse within 15 cm of the battery terminal even for a small strip.
- Connecting the strip at one end only for runs over 5 m: long strips have resistance, so the far end dims under voltage drop. Feed from both ends with equal wire lengths, or split the run into two shorter sections each fed from the PSU.
- Mismatching strip voltage: connecting a 24V strip to a 12V supply gives about 25% brightness. Connecting a 12V strip to a 24V supply will instantly destroy the LEDs. Check the label before connecting.
- Running max-wattage strips in enclosed channels: high-density strips (24 W/m+) generate significant heat. Aluminium extrusion channels act as heatsinks and are not optional at these densities.
Frequently Asked Questions
How long can a 12V LED strip run be before I need to inject power?
For a 14.4 W/m strip at 6 A, a single wire feed from one end becomes noticeably dimmer beyond about 5 m at 1.5 mm² wire or about 8 m at 2.5 mm². The solution is power injection: run a second pair of wires from the PSU to the midpoint or far end of the strip, connecting to the +12V and GND pads at that point. This halves the effective current per wire. For runs over 10 m, inject at both ends and the midpoint. Use the Wire Gauge Calculator with half the strip length as the run when injecting from both ends.
Can I cut LED strips to a custom length?
Yes, but only at the marked cut points — typically every 3 LEDs (about 5 cm for high-density strips, 10 cm for standard). Cutting between marked points leaves partial LED groups that cannot function. After cutting, solder wires directly to the copper pads at the cut point, or use snap-on LED strip connectors. Seal exposed copper with silicone or use an IP65-rated strip if moisture is present.
What is the difference between 12V and 24V LED strips?
24V strips run at half the current for the same wattage, which means thinner wire, less voltage drop on long runs, and better dimming performance at low brightness levels. The trade-off is that 24V PSUs cost slightly more and 24V strips are slightly less common. For runs under 5 m and total power under 50W, 12V is simpler. For longer runs or higher-wattage installs, 24V is the better choice. Use the Watts / Volts / Amps Calculator to compare current at both voltages.
Do I need a resistor to run LED strips?
No — LED strips already have resistors built into each segment. Unlike individual LEDs, strips are designed to connect directly to the rated voltage (12V or 24V) with no external resistor. The resistors visible as small brown rectangular components on the strip PCB set the current for each LED group. For individual LEDs not on a strip, you do need a current-limiting resistor — use the LED Resistor Calculator for that.