LED Strip Lights Wiring Diagram

LED Strip Lights Wiring Diagram — interactive diagram. Open it in the editor to customise components and wiring.

This is a free printable led strip lights wiring diagram: download the diagram as SVG or open it and print to paper or PDF.

LED strip lights run on 12 V or 24 V DC from a constant-voltage driver; long runs require voltage-drop calculations to prevent dim ends, and RGB strips use a common-anode 4-pin connection.

LED strip lights are constant-voltage DC devices, not constant-current — this is a critical distinction. The strip contains its own current-limiting resistors (typically one resistor per group of 3 LEDs for 12 V strips, or per group of 6 LEDs for 24 V strips). The driver must supply a stable, regulated DC voltage matching the strip's rating: 12 V or 24 V. Connecting a 12 V strip to a 24 V driver doubles the LED current and destroys the strip instantly.

The most important real-world constraint is voltage drop across long runs. Copper traces on a flexible PCB have finite resistance. A 5-metre run of standard-density 12 V strip (typically 14.4 W/m) draws 1.2 A/m, or 6 A for the 5-metre length. Even at moderate trace resistance, the far end of the strip can sit 1–2 V below the supply voltage, causing visible dimming. At 12 V this is proportionally far worse than at 24 V (a 1 V drop is 8.3% of 12 V but only 4.2% of 24 V), which is why 24 V strips are preferred for runs longer than approximately 5 metres.

The remedy is parallel power injection: run a separate wire from the driver positive and negative terminals to the mid-point or far end of the strip, injecting supply voltage at multiple points. Never simply daisy-chain strips end-to-end from one feed point for long runs.

RGB LED strips have four conductors: one common anode (+12 V or +24 V) and three cathodes, one per colour channel (Red, Green, Blue). An RGB controller or LED driver switches the negative (cathode) side of each channel using transistors or MOSFETs. The common-anode configuration means the positive rail is always connected; individual colours are enabled by grounding their respective cathode through the controller.

RGBW strips add a fourth (White) channel with its own cathode, requiring a 5-pin connection and RGBW-capable controller. Addressable strips (such as WS2812B) carry their own integrated ICs per LED segment and are controlled by a serial data signal — these are not covered under simple constant-voltage wiring.

How to wire led strip lights wiring diagram

Calculate the total load and select the driver Determine total strip length and wattage per metre. Multiply to get total watts. Add 20% headroom and select a constant-voltage LED driver of matching voltage (12 V or 24 V) at or above the calculated watt rating. Confirm the driver's output voltage matches the strip specification exactly.
Plan the cable run and power injection points For runs exceeding 5 m (12 V) or 10 m (24 V) from a single feed, plan intermediate power injection points. Use the voltage-drop formula V = I × R to calculate the voltage at the far end. Conductor cross-section for the feed wires should be sized to limit voltage drop to less than 3% of supply voltage.
Cut the strip at designated cut marks only LED strips must only be cut at the marked cut points (indicated by a scissor icon or copper pads at regular intervals, typically every 50 mm for 12 V/60 LEDs per metre strips). Cutting elsewhere breaks the internal series resistor group and destroys that LED segment.
Connect the strip to the driver output The driver's positive (+) output connects to the strip's positive (+) solder pad or connector pin. The driver's negative (–) output connects to the strip's negative (–) pad. For RGB, connect V+ to the common anode and each colour cathode (R, G, B) to the corresponding controller output. Verify polarity before powering on — LED strips are polarity sensitive.
Add parallel injection cables for long runs For long runs, run separate positive and negative cables from the driver directly to the mid-point or far end of the strip. Connect them to the strip's solder pads at that point. This halves the effective electrical length of the run and reduces voltage drop proportionally.
Power on and test Energise the driver and verify all LED segments are the same brightness. Walk the length of the run visually comparing brightness. Measure DC voltage at the far end using a multimeter — it should be within 3% of the driver output voltage. For RGB, verify all three channels respond correctly to the controller.

Specifications

Operating voltage (standard strips)	12 V DC or 24 V DC (constant voltage)
Typical strip wattage	4.8 W/m (30 LEDs/m) to 28.8 W/m (240 LEDs/m) — strip specific
RGB connector pinout (common-anode)	4 pins: V+ (common anode), R (cathode), G (cathode), B (cathode)
Maximum run length from single feed (12 V)	~5 m before visible voltage-drop dimming (load-dependent)
Maximum run length from single feed (24 V)	~10 m before visible voltage-drop dimming (load-dependent)
IP rating range	IP20 (indoor, non-damp) to IP68 (submersible) — product specific
LED colour rendering index (CRI)	Typically CRI 80–95+ depending on product grade

Safety warnings

The LED strip itself operates at SELV (Separated Extra-Low Voltage — 12 V or 24 V DC) and is not directly shock hazardous. However, the LED driver's mains input side is live at 230 V or 120 V AC. Never work on the driver with the mains supply connected.
Running an LED strip at a voltage above its rating — even 12.5 V on a 12 V strip — increases LED and resistor temperatures, accelerating lumen depreciation and creating a fire risk in enclosed fittings.
LED strips installed in bathrooms must comply with IP rating requirements for each zone under IEC 60364-7-701, BS 7671 Chapter 70, or the applicable national standard. Check the IP rating of both the strip and driver for the zone of installation.
Driving an oversized strip load from an undersized LED driver causes the driver to operate above its rated output, shortening its life and potentially causing overheating and fire. Always include a 20% headroom margin.
This page provides illustrative reference information only. Installation of LED lighting connected to the mains supply should be carried out by a qualified electrician and must comply with applicable national wiring regulations.

Tools needed

Digital multimeter (voltage and current measurement)
Wire strippers with adjustable stop
Soldering iron and solder (for solder-type connections)
Heat-shrink tubing and heat gun (for insulating solder joints)
Tape measure (for strip length planning)
Scissors (for cutting strip at marked cut points only)
Clamp meter (for verifying load current against driver rating)

Common mistakes

Connecting a 12 V strip to a 24 V driver — the strip LEDs and resistors are immediately destroyed by double the rated current. Always verify driver output voltage matches the strip voltage printed on the PCB.
Chaining multiple 5-metre strips end-to-end from a single power injection point — voltage drop compounds with each additional strip, causing the far end to be visibly dimmer. Inject power at each strip connection point.
Cutting the strip at non-designated locations — only cut at the marked copper pads between groups. Cutting through a resistor pad destroys the current-limiting resistor for the preceding group.
Running the strip loose inside an enclosed recess without a heatsink channel — junction temperature rises, LEDs dim prematurely and fail. Always seat the strip in an aluminium extrusion for heat management.
Using the same RGB controller rated for 12 V on a 24 V installation — the controller MOSFETs and protection circuits are voltage-rated. Using an under-rated controller on 24 V will damage it.

Troubleshooting

Far end of the strip is noticeably dimmer than the near end: Cause: Voltage drop along the strip's PCB copper traces — excessive current for the run length and trace resistance Fix: Measure DC voltage at both ends of the strip. If the far-end voltage is more than 3% below the near-end, add parallel power injection at the mid-point or far end by running a separate feed cable from the driver.
One colour is missing or incorrect on RGB strip: Cause: Incorrect wiring of R, G, or B cathode channel to controller; failed MOSFET in controller; broken PCB trace at a cut point Fix: Disconnect and test each colour channel by directly grounding its cathode pad to the driver negative — if the colour lights up, the fault is in the controller wiring. If not, the strip PCB trace is broken and the strip section needs replacing.
Driver shuts down or flickers under load: Cause: Load exceeds driver rated output; poor connection causing intermittent resistance; driver overheating in an enclosed fitting Fix: Measure total strip current with a clamp meter and compare to driver rating. Check all connector joints for oxidation. Improve driver ventilation. If load exceeds rating, replace with a higher-wattage driver.

Frequently asked questions

Can I connect multiple LED strips in series to extend the length?

Series connection of constant-voltage LED strips is not recommended. Each additional strip adds resistance, further reducing voltage at the far end and causing progressive dimming. Always connect strips in parallel (both strips receiving supply from the driver), or use parallel power injection at regular intervals along one continuous strip run.

How do I calculate the power supply size for an LED strip installation?

Multiply the strip wattage per metre by the total length in metres to get total watts. Add a 20% headroom margin. Example: 14.4 W/m × 5 m = 72 W; 72 W × 1.2 = 86.4 W minimum driver rating. Select the next available driver size above this figure. Never run a driver at 100% of its rated output continuously.

What is the maximum run length before voltage drop becomes a problem?

For 12 V standard-density strip (14.4 W/m) a practical limit is approximately 5 metres from a single feed point before visible dimming occurs. For 24 V strip of the same wattage the practical limit extends to approximately 10 metres. Beyond these lengths, inject power at intervals or select a higher-voltage constant-voltage system.

Why are the colours wrong on my RGB strip after fitting a new controller?

RGB controllers and strip connectors are not universally standardised. Some manufacturers wire R-G-B-V+, others V+-R-G-B, and pin order on 4-pin connectors varies. Check the controller's output labelling against the strip's PCB solder pads, which are usually labelled R, G, B, and + or V+. Swap the cathode leads until the colour output is correct.

Do LED strips need an earth connection?

LED strips operating on 12 V or 24 V SELV (Separated Extra-Low Voltage) do not require an earth connection on the strip itself. However, the LED driver's primary-side mains input must be correctly earthed. Metallic LED channel extrusions installed in bathrooms or damp locations may require equipotential bonding as part of the supplementary bonding scheme — consult local regulations.