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Technical reference
Key points
Key variances between the previous standard, BS 6651, and the IEC/BS EN 62305 - Technical reference table
BS 6651 Standard
(withdrawn August 2008)
IEC/BS EN 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 (IEC/BS EN 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
Specific tables relating to sizes and types of conductor
LPS components and conductors
and earth electrodes
LPS components - specifically related to BS EN 50164/IEC 62561
testing regimes
Annex B - guidance on application of BS 6651
IEC/BS EN62305-3 Annex E - extensive guidance given on application
of installation techniques complete with illustrations
Annex C - general advice (recommendation) for protection of electronic
IEC/BS EN 62305-4 is devoted entirely to protection of electrical and
equipment with separate risk assessment
electronic systems within the structure (integral part of standard) and is
implemented through single separate risk assessment (IEC/BS EN 62305-2)
Definition of risk
Risk (of death/injury) level set at 1 in 100,000 (1 x 10
-5
) based
3 primary risk levels defined (IEC/BS EN 62305):
on comparable exposures (smoking, traffic accidents, drowning etc)
–
R
1
Loss of human life (including permanent injury) 1 in 100,000 (1 x 10
-5
)
–
R
2
Loss of service to the public 1 in 10,000 (1 x 10
-4
)
–
R
3
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
Mesh arrangement, protective angle method, catenary system, extensive use
termination network
of air finials, all form part of or all of air termination network
2 levels of Lightning Protection mesh design:
4 sizes of mesh defined according to structural class of
(20 m x 10 m; 10 m x 5 m)
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:
4 levels of down conductor spacing dependent on structural class of
20 m & 10 m
Lightning Protection System:
– Class I 10 m – Class II 10 m
– Class III 15 m – Class IV 20 m
Use of bonds promoted to minimize side flashing
Extensive sections/explanations provided on equipotential bonding
10 Ω overall earthing requirement, achieved by 10 x number of
10 Ω overall earthing requirement achieved either by Type A
down conductors
arrangement (rods) or Type B arrangement (ring conductor)
Requirement to bond all metallic services, (gas, water, electricity etc) to
Requirement to bond all metallic services to main equipotential bonding bar.
main earth terminal along with external down conductor
‘Live’ electrical conductors (e.g. power, data, telecoms) bonded via
Surge Protective Devices (SPDs)
Use of bonds promoted to minimize side flashing
Via mounting fixtures
Rolling sphere concept on structures over 20 m tall:
4 sizes of rolling sphere concept defined according to structural class of
20 m sphere used on highly flammable contents/electronic equipment
Lightning Protection System:
within building 60 m sphere all other buildings
– Class I 20 m – Class II 30 m
– Class III 45 m – Class IV 60 m