Lightning protection ‘Separation Distance’ concept
Trevor Manas, Pontins
Electricity+Control, January 2016 (pages 24 – 28)
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An isolated Lightning Protection System (LPS) prevents partial lightning currents from entering protected space via electrical equipment or plant, in areas that are vulnerable to direct lightning strikes. The ‘Separation Distance’ concept is the measures employed when an Isolated Air Termination System is required. In accordance with the SANS / IEC Code 62305  series: ‘An isolated external LPS should be used when the flow of the lightning current into bonded internal conductive parts may cause damage to the structure or its contents’.
In other words; an isolated LPS should be installed to prevent partial lightning currents from entering into protected space via electrical equipment or plant situated in areas that are vulnerable to direct lightning strikes. Special problems occur when plant and equipment are installed to roofs and these elements are vulnerable to direct lightning strikes, these vulnerable elements require additional protection measures. If the roof mounted plant and equipment is connected directly to the external LPS, then, in the event of a direct lightning strike, partial lightning currents are conducted into the structure.
- There are applications requiring isolated LPSs.
- Isolated LPSs prevent the flow of partial lightning currents into sensitive systems.
- Standard techniques can be used to determine suitable separation distances.