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Key points Guide to BS EN/IEC 62305
TSC-0912 - 09.10.12
BS 6651 standard (withdrawn August 2008) BS EN/IEC 62305 standard
Document structure
118 page document, including 9 pages devoted to
risk assessment
Over 470 pages in 4 parts, including over 150 pages
devoted to risk assessment (BS EN/IEC 62305-2)
Focus on Protection of Structures against Lightning Broader focus on Protection against Lightning including
the structure and services connected to the structure
Specific tables relating to choice and dimension of
LPS components and conductors
Specific tables relating to sizes and types of conductor
and earth electrodes.
LPS components - specifically related to BS EN 50164/
IEC 62561 testing regimes
Annex B - guidance on application of BS 6651 BS EN/IEC 62305-3 Annex E - extensive guidance given
on application of installation techniques complete with
illustrations
Annex C - general advice (recommendation) for
protection of electronic equipment with separate risk
assessment
BS EN/IEC 62305-4 is devoted entirely to protection of
electrical and electronic systems within the structure
(integral part of standard) and is implemented through
single separate risk assessment (BS EN/IEC 62305-2)
Definition of risk
Risk (of death/injury) level set at 1 in 100,000
(1 x 10 -5) based on comparable exposures
(smoking, traffic accidents, drowning etc)
3 primary risk levels defined (BS EN 62305):
R1 loss of human life 1 in 100,000 (1 x 10-5)
R2 loss of service to the public 1 in 10,000 (1 x 10 -4)
R3 loss of cultural heritage 1 in 10,000 (1 x 10-4)
Protection measures
Mesh arrangement is promoted as the commonly
used means of air termination network
Mesh arrangement, protective angle method, catenary
system, extensive use of air finials, all form part of or all
of air termination network
2 levels of Lightning Protection mesh design:
(20 m x 10 m; 10 m x 5 m)
4 sizes of mesh defined according to structural class
of Lightning Protection System:
Class I 5 m x 5 m Class II 10 m x 10 m
Class III 15 m x 15 m Class IV 20 m x 20 m
2 levels of down conductor spacing:
20 m & 10 m
4 levels of down conductor spacing dependent on
structural class of Lightning Protection System:
Class I 10 m Class II 10 m
Class III 15 m Class IV 20 m
Use of bonds promoted to minimise side flashing Extensive sections/explanations provided on
equipotential bonding
10 ohm overall earthing requirement, achieved by
10 x number of down conductors
10 ohms overall earthing requirement achieved either
by Type A arrangement (rods) or Type B arrangement
(ring conductor)
Requirement to bond all metallic services, (gas, water,
electricity etc) to main earth terminal along with external
down conductor
Requirement to bond all metallic services to main
equipotential bonding bar. ‘Live’ electrical conductors
(e.g. power, data, telecoms) bonded via Surge
Protective Devices (SPDs)
Rolling sphere concept on structures over 20 m tall:
20 m sphere used on highly flammable contents/
electronic equipment within building
60 m sphere all other buildings
4 sizes of rolling sphere concept defined according to
structural class of Lightning Protection System:
Class I 20 m Class II 30 m
Class III 45 m Class IV 60 m
The following table gives a broad outline as to the key variances between the previous standard,
BS 6651, and the BS EN/IEC 62305.