ERICO ISODC Isolated Downconductor System - Manual (Page 7)

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As shown in Figure 2, the ERITECH ® Isolated Downconductor system requires two meters of clearance between the top of the
isolated mast and mounting brackets/protected equipment. This two meter clearance is sufficient to prevent a flash-over between
non-isolated air terminal and mast/object being protected.
IEC 62305 Electrical Insulation & Separation Distance
Equipment and structures can be protected by isolation, provided that the distance between the air terminal (or downconductor)
and items to be protected are separated by a separation distance greater than:
∝°
Figure 2. Protection angle and two meter minimum Isolated Mast height.
1m
≥2m
S = k
i
l
k
c
k
m
(IEC 62305-3 section 6.3, equation 4)
Where:
S separation distance, in meters
k
i
depends upon the selected class of LPS
k
c
depends upon the lightning current flowing on the downconductors (k
c
= 1 for a single downconductor, 0.5 for two
downconductors)
k
m
depends upon the electrical insulation material (k
m
= 1 for air)
l is the length, in meters, along the downconductor (from nearest equipotential bonding point, i.e. normally from lower
termination), to the point where the separation distance is being considered.
1. DESIGN
(continued)
Protected
Ki = Class of LPS (Lightning Protection Level)
0.08 I
0.06 II
0.04 III
0.04 IV
Table 3. k
i
versus Class of LPS.