Applicable to 12V and 24V DC LED Strip Light and Module Installations — Including High-Current Transformer Outputs up to 25A
1. Why Wire Gauge Matters
One of the most overlooked aspects of any LED installation is the selection of the correct wire gauge between the power supply (transformer) and the LED load. Many installers focus on choosing the right LED strip, driver, and voltage, yet undersize the cable connecting them — with consequences that range from poor light output to serious fire risk.
Wire is a conductor, but it is not a perfect one. Every length of wire has resistance, and that resistance causes two problems: voltage drop, which reduces the performance of your LEDs, and heat generation, which can damage insulation, connections, and in extreme cases cause electrical fires. The thinner the wire, the higher its resistance, and the worse both of these problems become.
Selecting the correct wire gauge is not optional — it is a fundamental safety and performance requirement of every LED installation.
2. Understanding Wire Gauge: AWG and mm²
Wire thickness is expressed in two common standards: AWG (American Wire Gauge), where a lower number means a thicker wire, and mm² (square millimetres of cross-sectional area), which is more commonly used in South Africa and most of Africa and Europe. The larger the mm² value, the thicker and more capable the wire.
For LED installations, the two most important factors that determine the correct wire gauge are:
• Current (Amps) — the total amperage the wire must carry, determined by the total wattage of the LED load divided by the supply voltage.
• Cable run length — the longer the wire run, the greater the total resistance, and the more critical it becomes to use a heavier gauge.
3. The Risk of Undersized Cable — Especially at High Currents
In low-voltage DC LED systems, current levels can be surprisingly high. This is particularly true for 12V systems, where a relatively modest wattage translates into significant amperage.
Consider a 300W 12V LED driver: at 12V, this draws 25 amps. At 24V, the same 300W load draws 12.5 amps. The lower the voltage, the higher the current for equivalent power — and the more critical correct cable sizing becomes.
⚠ WARNING: A 300W 12V power supply drawing 25 amps through undersized cable is a serious fire hazard. At 25A, even a short run of 1.5mm² cable will overheat. Never undersize cable on high-current installations.
Heat builds up in undersized wire proportionally to the square of the current — meaning that doubling the current quadruples the heat generated. At 25 amps, this effect is severe and can cause rapid insulation degradation, melted connectors, and fire.
4. Recommended Wire Gauges for LED Installations
The table below provides general guidance for wire gauge selection based on current load and run length. These are conservative, safe recommendations for LED DC wiring. Always consult a qualified electrician for final specification and compliance with local wiring regulations.
| Max Current | Min Wire Size | 12V Max Run | 24V Max Run | Typical Use |
| Up to 5A | 1.0 mm² | ~3m | ~6m | Small strip runs, single modules |
| Up to 10A | 1.5 mm² | ~4m | ~8m | Medium strip runs, 60–120W drivers |
| Up to 15A | 2.5 mm² | ~5m | ~10m | Larger strip runs, 150–180W drivers |
| Up to 20A | 4.0 mm² | ~5m | ~10m | High-output drivers, 200–240W |
| Up to 25A | 6.0 mm² | ~4m | ~8m | 300W drivers, large commercial runs |
Note: Run lengths above assume a maximum voltage drop of 3% and are indicative only. For longer runs, increase wire gauge or introduce intermediate feed points.
5. High-Current Transformers: 25A and Above
Large LED power supplies — commonly 300W at 12V — are increasingly used in commercial, hospitality, and landscape lighting installations where long runs of high-density LED strip are required. These drivers output up to 25 amps continuously, and the cable between the driver and the LED load must be sized accordingly.
At 25 amps, the minimum recommended wire size is 6.0 mm² for the output cable. This applies to both the positive and negative conductors. Using anything smaller risks overheating at the cable itself, at terminal connections, and at the strip’s solder pads or connectors.
In practice, many installers split the load from a single 300W driver across multiple shorter parallel runs, each fed with appropriately sized cable. This is the preferred approach as it reduces the current per run, allows lighter cable to be used per branch, and minimises voltage drop across the installation.
⚠ WARNING: Never connect a 25A power supply output to thin flex cable (0.5mm² or 0.75mm²) as commonly found in domestic lamp flex. This cable is rated for 3–6A maximum and will overheat immediately under high current loads.
6. Connector and Termination Ratings
Wire gauge alone is not sufficient — every connector, terminal block, junction, and solder point in the circuit must also be rated for the full current load. Common LED strip connectors and push-in strip clips are typically rated for 5–10A maximum. At 25A, these connectors will fail, arc, and potentially ignite surrounding materials.
For high-current installations, use:
• Screw terminal blocks rated for the full current, not push-in connectors.
• Correctly crimped ring or fork terminals at driver output connections.
• Soldered and heat-shrunk joins where inline connections are unavoidable.
• Bus bars or distribution blocks to split high-current feeds into multiple lower-current branch runs.
7. Practical Installation Guidelines
• Always calculate total current before selecting cable: Total Watts ÷ Voltage = Amps.
• Use 24V over 12V wherever possible for runs over 5 metres — it halves the current for the same wattage, allowing lighter cable and reducing voltage drop.
• Keep cable runs as short as possible between the power supply and the LED load. Locate drivers centrally to the load they serve.
• Feed from both ends on long strip runs to halve the effective current per cable and reduce voltage drop.
• Never bundle high-current DC cables tightly with other cables — heat dissipation requires airflow around the conductors.
• Label all cables with their voltage, current rating, and destination for ease of maintenance and fault-finding.
8. Quick Reference: Current by Driver Size
| Driver Rating | Voltage | Output Current | Min Cable Size |
| 60W | 12V | 5.0A | 1.0 mm² |
| 60W | 24V | 2.5A | 1.0 mm² |
| 100W | 12V | 8.3A | 1.5 mm² |
| 100W | 24V | 4.2A | 1.0 mm² |
| 150W | 12V | 12.5A | 2.5 mm² |
| 150W | 24V | 6.3A | 1.5 mm² |
| 200W | 12V | 16.7A | 4.0 mm² |
| 200W | 24V | 8.3A | 1.5 mm² |
| 300W | 12V | 25.0A | 6.0 mm² |
| 300W | 24V | 12.5A | 2.5 mm² |
9. Need Assistance?
For cable sizing advice, product specifications, or technical support on your LED installation, please contact The Lighting Zone:
Email: admin@thelightingzone.co.za
Tel: +27 10 590 6101
Website: www.thelightingzone.co.za