Garden Lighting Voltage Drop Calculator
Check voltage drop compliance for garden lighting circuits with the stricter 3% limit
Garden Lighting Quick Facts
- Lighting circuits have stricter 3% voltage drop limit (not 5%)
- LED drivers sensitive to low voltage - may flicker or fail
- Typical cable: 1.5mm² (29 mV/A/m) or 2.5mm² (18 mV/A/m)
- Long garden runs often need 2.5mm² despite low current
- SWA or armoured cable required for buried outdoor runs
Values from BS 7671 Table 4D1B (PVC copper at 70°C)
Need a Qualified Electrician?
Get quotes from vetted, local contractors for your garden lighting
Common Garden Lighting Scenarios
Patio lights near house (10m)
6A with 1.5mm² (29 mV/A/m). At 10m: (29 × 6 × 10) ÷ 1000 = 1.74V (0.76%) ✓
Path lighting to bottom of garden (30m)
6A with 1.5mm². At 30m: (29 × 6 × 30) ÷ 1000 = 5.22V (2.27%) ✓ but marginal
Extensive garden lighting (40m+)
6A with 2.5mm² (18 mV/A/m). At 40m: (18 × 6 × 40) ÷ 1000 = 4.32V (1.88%) ✓
Security floodlights (500W total)
~2.2A load. At 20m with 1.5mm²: (29 × 2.2 × 20) ÷ 1000 = 1.28V (0.56%) ✓
Festoon/party lights (long run 50m)
3A with 2.5mm². At 50m: (18 × 3 × 50) ÷ 1000 = 2.70V (1.17%) ✓
Complete Your Outdoor Setup
Need power to a garden office or outbuilding? Check submain voltage drop. Planning an EV charger on the driveway? Use our dedicated calculator. For cable sizing, see our cable sizing calculator.
Garden Lighting Voltage Drop
Garden lighting circuits must comply with the stricter 3% voltage drop limit - not the 5% allowed for power circuits. This is because lighting is more sensitive to voltage reduction. LEDs may dim, flicker, or fail completely if voltage drops too much. Long outdoor cable runs often require larger cables than the current alone would suggest.
Garden Lighting Installation Costs (2024)
Typical UK installation costs. Excludes light fittings.
| Installation Scenario | Materials | Labour | Total |
|---|---|---|---|
| Simple patio lights (5-10m) | £80-150 | £150-250 | £230-400 |
| Path lighting (20-30m) | £150-300 | £250-400 | £400-700 |
| Full garden scheme (40m+) | £300-600 | £400-700 | £700-1300 |
| Security lighting install | £100-250 | £150-300 | £250-550 |
| Outdoor consumer unit | £120-250 | £150-250 | £270-500 |
Prices as of 2024. Actual costs vary by region and ground conditions.
Why the 3% Limit Matters
BS 7671 Regulation 525 specifies 3% maximum voltage drop for lighting. On a 230V supply, that is just 6.9V. LED drivers are particularly sensitive - some require minimum input voltage and will not operate correctly below it. Incandescent bulbs dim proportionally with voltage, but LEDs may cut out entirely.
LED Driver Considerations
LED drivers convert mains voltage to the low voltage LEDs need. Most drivers specify minimum input voltage (often 200-220V). If your supply drops below this due to voltage drop, the driver may shut down, flicker, or reduce output. Quality drivers handle wider input ranges but always check specifications.
Frequently Asked Questions
Related Electrical Calculators
Get Quotes from Local Electricians
Looking for a qualified electrician for your garden lighting installation? Tell us about your project and we'll connect you with vetted contractors in your area. Free, no obligation quotes.
Trade professional or electrical business? Use the form above and let us know - we offer lead referrals in your area, bulk calculation tools, and white-label partnerships for merchants and suppliers.
More Electrical Calculators
Voltage drop, cable sizing, conduit fill and more. All BS 7671 compliant, all free.
View All Calculators