Commercial waterproof festoon lights for contractors, venues and distributors. Custom E27/B22, 24V/230V and OEM/ODM outdoor string light systems for UK, EU and Australia projects.
How long can a 230V festoon system run? Cable size, wattage and voltage-drop calculations
There is no universal safe maximum length for a 230V festoon run: cable size, total connected watts, load distribution and installation conditions all affect the result. WENDADECO lists up to 100 m for its 230V system, but that product limit must still be checked against the actual lamps, cable and site conditions.
Is 100 m always acceptable?
No. Treat 100 m as the published maximum series length for the applicable WENDADECO 230V configuration, not as approval for every load or installation. The voltage at the final lamp depends on the supply voltage, conductor resistance, total load and where the lamps are connected along the run.
A calculation also does not replace checks for current-carrying capacity, overcurrent protection, connectors, temperature, mechanical support or the electrical rules in the project country. A qualified electrical professional should confirm the design for a mains-voltage installation.
A practical voltage-drop calculation
For a simple single-phase 230V example, first estimate current from the actual load: I ≈ P ÷ 230, where P is total input watts and I is amperes. For a simplified copper two-core cable with the entire load at the far end, an approximate resistive estimate is:
Voltage drop (V) ≈ 2 × L × I × ρ ÷ A
- L is the one-way cable distance from the feed to the load in metres.
- A is the cross-sectional area of one conductor in mm².
- ρ is taken here as 0.0175 Ω·mm²/m for copper at 20°C for an illustration.
- The factor 2 accounts for the outgoing and return conductors.
This simplified estimate assumes a resistive load (power factor 1), a 230V supply and conductor temperature near 20°C. It excludes cable reactance, connector resistance, supply variation and the effect of operating temperature. The IET describes voltage-drop calculation using cable millivolts per ampere per metre × design current × run length; use the data for the actual finished cable rather than a generic estimate. See the IET calculation example. IEC 60228:2023 covers conductor sizes and resistance values for finished power cables, including flexible copper conductors.
Illustrative 100 m comparison
The table shows an approximate drop if the full load is concentrated at the far end of a 100 m one-way run. It is a calculation example, not measured WENDADECO performance. The listed conductor sections are WENDADECO 230V cable options: round 2×1.0 or 2×1.5 mm², and flat 2×1.5 or 2×2.5 mm².
| Cable option | Load used in example | Approx. drop at far end | Share of 230V |
|---|---|---|---|
| Round cable, 2×1.0 mm² | 500 W / 1,000 W | 7.6 V / 15.2 V | 3.3% / 6.6% |
| Round or flat cable, 2×1.5 mm² | 500 W / 1,000 W | 5.1 V / 10.1 V | 2.2% / 4.4% |
| Flat cable, 2×2.5 mm² | 500 W / 1,000 W | 3.0 V / 6.1 V | 1.3% / 2.6% |
Worked example: a 1,000 W load at 230V draws about 4.35 A when power factor is assumed to be 1. For 2×1.5 mm² over 100 m, the simplified estimate is 2 × 100 × 4.35 × 0.0175 ÷ 1.5 ≈ 10.1 V, or about 4.4% of 230V. Actual cable resistance at operating temperature and the load's electrical characteristics may change the result.
What changes when lamps are spread along the line?
Festoon lamps are usually distributed across multiple sockets, so the full load does not necessarily flow through every metre of cable. For a distributed load, divide the run into sections: calculate the current passing through each section from the lamps downstream of it, calculate that section's drop, then add the drops to estimate the voltage at each point. Lamp spacing affects load distribution; the total lamp wattage and the position of each lamp still matter.
Project checklist before choosing a run length
- Add the actual input wattage of the lamps that will be connected. Do not use a socket's component limit as the planned total system load.
- Use the exact cable construction and conductor cross-section specified for the product; confirm its resistance and temperature rating from the cable data.
- Measure the one-way route and map where the loads sit. Recalculate each section when loads are distributed.
- Check the minimum voltage required by the lamps or drivers at the end of the run, plus local installation rules and protection requirements.
- Where the calculation is not satisfactory, ask the system supplier and a qualified electrician whether a shorter run, lower load or approved feed arrangement is suitable. Do not parallel supplies or add a second feed unless the product design expressly allows it.
FAQs
Can I connect 100 m of 230V festoon lights in one run?
WENDADECO lists a maximum series length of 100 m for its 230V system. The actual permitted run still depends on the applicable product configuration, total load, cable, connections and installation conditions.
Does choosing 2×2.5 mm² automatically make a longer run acceptable?
A larger conductor section generally reduces conductor resistance and the calculated voltage drop, but it does not by itself confirm current capacity, connector compatibility, mechanical suitability or compliance. Check the complete assembly and applicable local rules.
How should I calculate the total wattage?
Sum the input watts of the actual lamps intended for the line. For equipment with electronic drivers, use the manufacturer's input-current or power data and account for its electrical characteristics; nominal lamp watts alone may not describe current accurately.
Why can the last lamps appear dimmer?
Voltage drop is one possible cause, especially on a long, heavily loaded run. Loose or high-resistance connections, a low supply voltage, damaged cable or unsuitable lamps can also contribute, so inspect and test the system safely.
Does lamp spacing affect the voltage-drop estimate?
Yes. Spacing changes where load is drawn along the cable. A lumped load-at-the-end example is not the same as lamps distributed along the full run; use a section-by-section calculation for a real layout.
Is there one voltage-drop percentage that applies in every country?
No single percentage should be assumed for every product and installation. Follow the current wiring rules for the project location and the voltage requirements of the connected lamps or drivers. The IET notes that recommended installation voltage-drop values are informative and that connected-equipment requirements also matter.
Date: 22 October 2026
Author: Sales Manager, WENDADECO
