12-13 / 319
Guide to
| Surge Protection Devices
6
Where this is the case and for installations being supplied by
overhead lines, Regulation 443.2.2 indicates that provided the
impulse withstand voltage of the equipment is not less than
the values given in Table 44.3 (see Table 1 for installations
rated at 230 V to Earth), no additional protection by a SPD is
required. However, where higher levels of equipment reliability
or higher risks (e.g. fire) are expected, additional protection by
an SPD against over-voltage may be required.
Similarly, for an installation having overhead lines, no
additional protection against overvoltages is required if the
equipment meets the minimum voltage withstand values in
table 44.3.
There are some words of caution in the notes to this section
where it is recognised that transient over-voltages transmitted
by the supply distribution system are not significantly
attenuated. So an induced voltage some distance away
could easily manifest itself at the electrical installation and
cause potential harm to the equipment within. It is also worth
considering that the AQ data is for thunderstorm days NOT
lightning strikes. One storm will usually contain many lightning
flashes which could lead to an over-voltage on the installation
causing damage to equipment.
“where higher levels of equipment
reliability or higher risks (e.g.
fire) are expected, additional
protection by an SPD against
over-voltage may be required.”