ERICO 3000 ERITECH SYSTEM - Manual (Page 52)

INSTALLATION, OPERATION AND MAINTENANCE MANUAL
50
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Note: If the number of thunderdays
for the proposed installation site is
not known, but the ground flash
density is known, this value can be
converted to thunderdays using the
following table. This resulting value
can then be used in the figure 33.
When additional measures are required,
there are two basic approaches to reduc-
ing the otherwise unacceptable voltage
rise that would occur on the cable:
t3VOQBSBMMFM&3*5&$)&3*$03&DBCMFT
or
t3VOBTJOHMF&3*5&$) ® ERICORE cable,
but break it into several sections, none
of which exceeds the cable breakdown
voltage. This is done by periodically
connecting the cable to a conductive
structural point.
These methods are explained as follows.
However, if the result indicates that
additional measures are required, then a
single uninterrupted length of ERITECH
®
ERICORE cannot be run.
Although the flowchart allows lengths
of up to 87 m, ideally lengths should be
limited to 70 m to avoid any likelihood of
problems.
When determining the apparent length of
ERITECH
® ERICORE conductor required in
a particular situation it is prudent to make
the connection to the ground system at
the first available opportunity. The prac-
tice of running ERITECH ERICORE for long
horizontal lengths at the ground level to
reach a designated earth point is discour-
aged. Instead a lower termination should
be made to a suitable earthing point upon
reaching the ground or basement level,
then a separate length of conventional
grounding bonding conductor run to other
earthing points as required.
In the case of installations exceed-
ing the maximum single ERITECH
ERICORE cable length, the advice of
the ERICO application engineering group
should be sought. The following informa-
tion on the techniques used is intended as
a guide for installers and to provide back-
ground information.
Ground flash density
(strikes / km 2 / year)
Lightning activity
(thunderdays / year)
Up to 2.7 20
2.8 to 3.9 30
4.0 to 5.2 40
5.3 to 6.6 50
6.7 to 9.5 60
9.6 to 12.5 80
12.6 or more 100