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Guide to
| Surge Protection Devices
17
The following is a quick selection guide which may assist
in choosing whether SPD’s are required and the correct
type of device
• Does the installation contain a lightning protection system?
• Is the installation adjacent to any tall structure, tall trees or
near a hill top in a lightning prone area?
• Does the installation contain equipment where higher
reliability from overvoltages is required
If the answer is YES in the above to the first two questions,
it is recommended to install a Type 1+2 device. This will
provide protection against surges caused by direct lightning
strikes and provide protection against transient over-voltages
caused by indirect lightning strikes or by switching events.
If the answer is YES to the third question then it is
recommended to install Type 2 devices to provide protection
against transient over-voltages caused by indirect lightning
strikes or by switching events.
SPD quick selection guide
Risk of direct lightning
(see BS EN 62305) or
lightning protection
system installed?
(443.1.1)
Overhead line
supplying the building
at risk of direct strike -
see BS EN 62305
(443.1.1)
Installation presents
higher risk (e.g. fire) or
requires higher reliability from
overvoltages including switching
(443.2.2 Note) - see BS EN
62305.
No
Yes
Yes
Yes
No
No
Overvoltage protection
required. Install Type 1 or Type
1+2SPDs at distribution
board/consumer unit to
prevent dangerous flashover
(534.2.1)
Co-ordinated set of
overvoltage SPDs for
equipment protection e.g.
Type 2 or Type 2+3 for
distribution boards feeding
sensitive electronic equipment
(534.2.6).
Protection against overvoltage
is not required (443.1.1,
443.2.2) if equipment impulse
withstand voltage to Table
44.3
SPD decision flow chart for installations
within the scope of this guide
Note:
For larger installations beyond the scope of this guide, a risk assessment method
used to evaluate the need for SPDs is given in Section 443 of BS 7671:2008(2011)