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no direct equipotential bonding
connection between BLITZDUCTOR
and the terminal device
2 2’ 1’
BLITZDUCTOR
1
BXT ML2 BD 4’ protected 3’
180
3
4
BLITZDUCTOR 2’ 1’
1
2
BXT ML2 BD 4’ protected 3’
4
3
U p 180
discharge current U L incorrect! U r incorrect! U r
U R
Due to incorrect cable routing, interference is injected
L and R of the cable decrease U r : U r = U p + U L + U R from the unprotected to the protected cable
Figure 8.2.5.3 Incorrectly established equipotential bonding Figure 8.2.5.4 Incorrect conductor routing
potential bonding conductor must be installed separately, if Shielding
possible, and / or designed to have extremely low impedance Cable shielding is described in section 7.3.1.
(e.g. metal mounting plate). This type of installation is the com-
mon installation practice for class I terminal devices. Installation recommendations
The use of metal shields or cable ducts reduces the interaction
U =U +U between the pair and the environment. For shielded cables, the
r p v
following must be observed:
Example 3: Incorrectly established equipotential
bonding (Figure 8.2.5.3) ¨ Shield earthing at one end reduces the radiation of electric
The terminal device is only directly earthed via the protective fields
conductor terminal, for example. There is no low-impedance ¨ Shield earthing at both ends reduces the radiation of elec-
equipotential bonding to the protective device. The path of the tromagnetic fields
equipotential bonding conductor from the protective device to ¨ Conventional shields do not provide sufficient protection
the protective conductor terminal of the terminal device (e.g. against low-frequency magnetic fields
equipotential bonding bar) considerably influences the resid-
ual voltage. Depending on the cable length, voltage drops up Recommendations
to some kV can occur which add up to U p and can lead to the Shields should run continuously between information tech-
destruction of the terminal device due to a high residual volt-
age level at the device input. nology installations, have a low transfer impedance and be
conducted around the complete circumference, if possible. The
Example 4: Incorrect conductor routing shield must completely enclose the cables, as far as practica-
(Figure 8.2.5.4) ble. Interruptions in the shield as well as high-impedance earth
Even if equipotential bonding is carried out correctly, incorrect connections and “pig tails“ should be avoided.
conductor routing can interfere with the protective effect or The extent to which low-voltage lines can influence telecom-
even damage the terminal device. If strict spatial separation munication lines depends on many factors. The recommended
or shielding of an unprotected cable upstream of the SPD and values for the spatial distances to low-voltage lines are de-
a protected cable downstream of the SPD is not observed, the scribed in EN 50174-2. For a cable length less than 35 m, typi-
electromagnetic interference field can cause injection of inter- cally no separation distance has to be maintained. In all other
ference impulses on the protected cable side. cases, Table 8.2.5.1 gives the separations which apply.
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