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1’
protected protected 3’
2’ 4’
BLITZDUCTOR BXT ML4 BD EX 24
2 4
voltage supply 1 3 terminator
(FISCO)
U o ≤ 17.5 V
I o ≤ 380 mA
segment 1
protected
3’ 4’ EX 24 BXT ML4 BD 4 3
segment 2
1’ 2’ BLITZDUCTOR 2 1
voltage supply
(FISCO)
U o ≤ 17.5 V
I o ≤ 380 mA protected 3 4 1 2 4 3 1 2 terminator
EX 24
EX 24
BXT ML4 BD
field side
BXT ML4 BD
BLITZDUCTOR
BLITZDUCTOR
(FISCO)
Field bus FISCO
protected 4’ 2’ protected protected 4’ 2’ protected U i ≤ 17.5 V
No. Surge protective device Part No. 3’ 1’ 3’ 1’ I i ≤ 380 mA
P i ≤ 5.32 W
BLITZDUCTOR XT – BXT ML4 BD EX 24 920 381 C i ≤ 5 nF
L i ≤ 10 mH
BLITZDUCTOR XT – BXT ML2 BD S EX 24 920 280
Figure 8.2.4.3 SPDs in intrinsically safe bus systems – Insulation strength > 500 V a.c.
the voltage of the intrinsically safe circuit or 500 V, whichever To prevent that the voltage drop of the interference current
value is higher. Equipment with an insulation strength < 500 V to be discharged in the earth connection deteriorates the
a.c. is considered to be earthed. voltage protection level, consistent equipotential bonding
Intrinsically safe equipment (e.g. cables, measuring transduc- must be established between the device to be protected and
ers, sensors) generally has an insulating strength > 500 V a.c. the SPD.
(Figure 8.2.4.3).
Earthing / Equipotential bonding
Intrinsically safe circuits must be earthed if this is required for Consistent equipotential bonding and intermeshing of the
safety reasons. They may be earthed if this is required for func- earth-termination system in the hazardous area of the instal-
tional reasons. This earthing must be carried out at only one point lation must be ensured. The cross-section of the earthing con-
by connecting them with the equipotential bonding system. If ductor between the SPD and the equipotential bonding system
2
the d.c. sparkover voltage to earth of the SPD is < 500 V d.c., must be at least 4 mm (copper). When using several SPDs, a
2
the intrinsically safe circuit is considered to be earthed. cross-section of 16 mm (copper) is recommended.
If the d.c. sparkover voltage of the SPD is > 500 V d.c., the
intrinsically safe circuit is not considered to be earthed. Installation of BLITZDUCTOR XT in Ex(i) circuits
BLITZDUCTOR XT (BXT ML4 BD EX 24 or BXT ML2 BD S EX 24) The normative requirements for Ex(i) circuits with regard to
meets this requirement. explosion protection and electromagnetic compatibility (EMC)
In order to coordinate the dielectric strength of the devices correspond to different points of view, a situation which occa-
to be protected (measuring transducer and sensor) with the sionally causes consternation among designers and installers.
voltage protection level of the SPD, it must be ensured that the The most important selection criteria for intrinsic safety and
insulation strength of the devices to be protected is consider- EMC / surge protection in installations are listed in chapter
ably higher than the requirements for an a.c. test voltage of 9.32 to identify the interaction of the requirement profile in
500 V a.c. each case.

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