UFC 3 -520-01
June 10, 2002
D-2.4.4 Table D-3 provides the minimum allowed surge current ratings per phase or
per mode of protection. The surge current ratings have been selected based on
ensuring an adequate margin for higher -than-expected surges due to nearby lightning
strikes. Higher s urge current ratings can be selected provided there is not a significant
cost difference.
Table D -3. Minimum Allowed Surge Current Rating
Minimum Surge Current
AC Power
Rating Per Phase or Per
System Location
Mode of Protection
Service Entrance
80,000 amperes
Sub-Panels
40,000 amperes
Critical Loads
40,000 amperes
D-2.4.5 The surge current ratings specified in Table D -3 apply regardless of whether
the facility is located in a high, medium, or low exposure area (as defined by IEEE
C62.41. The selected minimum surge current values are based on the following
rationale:
The values are high enough to ensure protection in high exposure areas.
The values are not so high that lower exposure areas are over -protected.
This approach does not force each designer to decide if a given facility is located in
a high, medium, or low exposure environment.
D-2.5
Repeated Surge Current Withstand Capability. The specified surge
current ratings are intended to provide an adequate allowance for repeated surges over
the life of the surge protector. In addition to the specified surge current ratings, verify
that the manufacturer has tested representative surge protectors to the following IEEE
C62.41 levels, as a minimum:
A minimum of 1,000 operations at 500 amperes, 100 kilo-Hertz ring wave.
A minimum of 1,000 operations at 3,000 amperes, 8/20 sec combination wave.
A minimum of 40 operations at 10,000 amperes, 8/20 sec combination wave.
A minimum of 1 operation at 20,000 amperes, 8/20 sec combination wave (one in
each polarity).
D-5
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