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L1 L2 L3 N PE

sub-distribution board
type 2 surge arrester
125 A
4 x DG S 275 Part No. 952 070
1x DK 25 Part No. 952 699
DEHNguard DG MOD 275 DEHNguard DG MOD 275 DEHNguard DG MOD 275 Feed-Through Terminal DK 25 DEHNguard DG MOD 275 1x MVS 1 4 Part No. 900 610
1x MVS 1 2
Part No. 900 617

DEHNbloc ®
coordinated type 1
L/N L’/N’ L/N L’/N’ L/N L’/N’ L/N L’/N’
315 A lightning current arrester

DEHNbloc DB H MOD 255 DEHNbloc DB H MOD 255 DEHNbloc DB H MOD 255 Feed-Through Terminal DK 25 DEHNbloc DB H MOD 255 4x DB M 1 255 Part No. 961 120 main distribution board
1x DK 25 Part No. 952 699
1x MVS 1 6 Part No. 900 815
1x MVS 1 2 Part No. 900 617
N/PE(N) N/PE(N) N/PE(N) N/PE(N)

MEB
Only required, if no fuse of the same or a lower
nominal value is provided in the upstream system.
Figure 8.1.5.4 SPDs used in a 230/400 V IT system – With incorporated neutral conductor (3+1 circuit)

8.1.6 Determination of the correct connecting Figure 8.1.6.1. To this end, no separate cable branches are
cable lengths for SPDs used for connecting the surge protective devices.
The determination of the correct connecting cable lengths for
surge protective devices is an integral part of the IEC 60364-5-53 Parallel connection in accordance with IEC 60364-5-53
(HD 60364-5-534) standard. (HD 60364-5-534)
The aspects described below are also frequent reasons for The optimal series connection cannot be used for all system
complaints by experts, members of technical inspectorates, conditions.
etc. who inspect the installation. The nominal currents, which are conducted via the double
terminals on the surge protective device in case of series
Series connection in accordance with IEC 60364-5-53 connection, are limited by the thermal withstand capability
(HD 60364-5-534) of the double terminals. For this reason, the manufacturer of
The impulse voltage level which is actually applied to the the surge protective device prescribes a certain maximum
installations to be protected is crucial for protecting instal- permissible value for the backup fuse which means that se-
lations, equipment and loads. An optimum protective effect ries connection can sometimes not be used for systems with
is achieved if the impulse voltage level at the installation to higher nominal operating currents.
be protected is equal to the voltage protection level of the
surge protective device. Meanwhile, so-called two-conductor or pin-shaped termi-
Therefore, IEC 60364-5-53 (HD 60364-5-534) suggests nals are available which allow to better solve this problem.
to connect surge protective devices in series as shown in Thus, cables can be kept short, even if the nominal operating

234 LIGHTNING PROTECTION GUIDE www.dehn-international.com