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Guide to
| Surge Protection Devices
10
The specifier should ascertain from BS 7671 which
connection type is preferable (CT 1 or CT 2). Hager
manufacture devices with connection type CT2.
Type 1 devices need to be selected such that the value if I
imp
is not less than that which shall be calculated in accordance
with BS EN 62305-4. However if this cannot be calculated
then this value shall be not less than 12.5kA. Also, due to the
connection method, the value of I
imp
between the neutral
conductor and the protective conductor shall be not less
than 50kA for three phase systems and 25kA for single phase
where the value cannot be calculated.
For Type 2 devices the value of I
n
shall be not less than 5kA
and the value between the neutral and protective conductor
shall be not less than 20kA for three phase systems and 10kA
for single phase. Larger values may be required as classified
in BS EN 61643-11.
534.2.3.4 also gives guidance as to the selection of an
appropriate device.
“The specifier should ascertain
from BS 7671 which connection
type is preferable. Hager
manufacture devices with
connection type CT2.”