MO.tool
STANDARDS & FORMULAS

Lightning Protection

Lightning protection: the risk assessment, the class, the system on the roof, the earthing and the sheet.

Standards and regulations

  • IEC / BS EN 62305-2
    Protection against lightning - risk management

    R1 against RT = 1 × 10⁻⁵, for the building as it is and with each class.

  • IEC / BS EN 62305-3
    Physical damage to structures and life hazard

    Mesh size, rolling sphere, protective angle and down conductor spacing by class.

  • IEC 62305-4
    Electrical and electronic systems within structures

    The surge protection (SPD) notes.

  • BS 7430
    Protective earthing of electrical installations

    One rod’s resistance and how many rods for the target.

Formulas

Risk check

R1 ≤ RT = 1 × 10⁻⁵ → the class needed

Design rules it applies

  • Mesh (Faraday cage), air rods (protective angle) or both
  • A test joint and an earth pit on every down conductor

For reference. MO.tool works these out to help your design; the engineer remains responsible for it. Always check the edition of each standard your project uses and the requirements of the local authority (DEWA, ADDC, Civil Defence…).

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