ERICO TSG Series Surge Reduction Filters (TSG-RSF) - Manual (Page 18)

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Earthing
Figure 14. Preferred approach
to equipotential bonding.
6.4 EARTHING
The earths for all site equipment should
be integrated (preferably deploying a single
point earthing approach) and an
equipotential earth plane should be created.
Integral to this is the elimination of earth
loops. It is common, but incorrect from the
point of lightning protection, for there to be
separate earths for various services, for exam-
ple electricity mains, telephone, computer
equipment and other building services.
For sites where the interconnection of these
earths is difficult, either for practical or
regulatory reasons, the use of a Transient
Earth Clamp (TEC) is recommended. The TEC
behaves as an open circuit under normal
operation, but under surge conditions it
activates to effectively clamp individual
points together.
The effectiveness of an SRF is intimately
related to the impedance presented by the
earthing system to which it is connected. A
low impedance route to the earth is required
(less than 10Ω). This can be achieved by
ensuring that the earth electrode system
at the site presents a low surge impedance
with respect to the ground. Additionally, the
interconnecting cabling must be of adequate
cross sectional area and be routed to provide
as short and direct a path as is practical.
Ideally the earthing system impedance should
be measured using a meter which simulates
the typical wave shape of a lightning
transient. ERICO
® can provide this service.
The earth conductor for the SRF should be
sized according to local regulations but with
a minimum size of 6 mm
2 . Every attempt
should be made to limit the cable length to
under 5 metres.
By selecting the most direct route, with the
minimum possible number of bends to the
earth point or internal earth bar, the risk of
side flashing and excessive voltage rise across
the equipment is reduced. Figure 14 depicts
the correct earthing concept as described
above.
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