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Cables, voltage drop, and earthing

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What is under the road, and why it matters.

Learning Track · Module 1: The network · Step 4 of 101

Showing content for Europe. Change the region at the top of the page.

Europe, Middle East, South Asia: Most circuits use armoured cable buried along the road, with copper or aluminium cores and PVC or XLPE insulation Europe: (IEC 60502-1) Middle East: (IEC 60502-1 or BS 5467) South Asia: (IS 7098 or IS 1554).

USA: City-owned circuits usually use direct-buried cable or wire in conduit (NEC Article 300 and 310). Utility-owned lights take power from overhead secondary conductors (NESC).

Voltage drop

The voltage drop increases with the cable length and the current. It decreases with a larger cable cross-section. The last pole on a long circuit gets the lowest voltage.

  • Europe, Middle East: IEC 60364-5-52 gives recommended limits. Many specifications use 3% to 5% at full load.
  • South Asia: Many Indian specifications limit the drop to about 5% at full load.
  • USA: The NEC informational notes suggest 3% for a branch circuit and 5% in total.
    • Measure the voltage at the last pole at full power. Check the result with the voltage drop tool.
    • An LED retrofit decreases the current, so an old circuit usually has less voltage drop after the retrofit.

    Earthing and grounding

    Europe:

    The earthing system (TN-S, TN-C-S, or TT, per IEC 60364) decides how the protection works. Class I luminaires need a protective earth. Class II luminaires have double insulation and no earth connection. Many European cities now use Class II for more safety when the earth path is poor. IEC 60364-7-714 gives the rules for outdoor lighting.

    Middle East:

    Most GCC authorities follow IEC 60364 or BS 7671 principles, with their own wiring regulations. Each metal pole and the feeder pillar must connect to earth. Sandy, dry soil can give high earth resistance. Use deeper rods or treated electrodes where tests show high values.

    South Asia:

    IS 3043 is the Indian code of practice for earthing. Each feeder pillar needs an earth pit, and each metal pole must connect to earth. Many tenders ask for a pit at the pillar and at regular pole intervals.

    USA:

    NEC Article 250 covers grounding and bonding. Each metal pole must connect to the equipment grounding conductor. A ground rod at the pole alone is not an effective fault path. The equipment grounding conductor from the source does that job.

    Note

    Measure earth resistance once a year, in the dry season, and write the result in the asset record.

    Sources

    1. IEC 60502-1 Power cables with extruded insulation (rated voltages 1 kV and 3 kV)
    2. IEC 60364-5-52 Selection and erection of electrical equipment: wiring systems
    3. IEC 60364-5-54 Earthing arrangements and protective conductors
    4. IS 3043 Code of practice for earthing
    5. NFPA 70 National Electrical Code, Article 250

    Changes: 30 October 2026: First publication: guides for Europe, the Middle East, South Asia, and the USA; failure library; tender clause library; comparisons; tools; downloads. See the changelog. Found a mistake? Report it.

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