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take note
EARTHING + LIGHTNING PROTECTION
When cascading SPDs exist, the coordination conditions (s clause 5)
should be considered. The corresponding performance parameters
with respect to the lightning protected zones (LPZ) are listed in
Table 3
.
Table 3: Selection aid for rating SPDs for the use in (zone) interfaces
according to IEC61312-1 [5] / IEC61000-4-5 [6].
Lightning protection zone
IEC 61312-1
LPZ 0/1
LPZ 1/2
LPZ 2/3
Range
of surge
values
10/350 0,5 – 2,5 kA ---
---
1,2/50
8/20
---
0,5 – 10 kV
0,25 – 5 kA
0,5 – 1 kV
0,25 – 0,5 kA
10/700
5/300
4 kV
100 A
0,5 – 4 kV
25 – 100 A
---
Require-
ments to
SPDs
(Category
from
Table 3, EN
61643 21)
SPD (j) a)
D1 or B2
---
No resistive
connection
to the out-
side of the
building
SPD (k) a)
---
C2 or B2
---
SPD (l) a)
---
---
C1
a)
SPD (j, k, l), see
Figure 3
NOTE: The range of surge values indicated under LPZ 2/3 includes
typical minimum resistibility requirements and might be implemented
into the equipment.
Figure 3: Coordination of two SPDs.
Key
U
IN2
: UIN ITE - open circuit voltage of the generator used for resistibility
verification
I
IN2
: IIN ITE - short circuit current of the generator used for resistibility
verification
U
P
- voltage protection level
I
P
- let through current
Figure 4: Necessary installation conditions of a 3, 5 or multi-terminal
SPD with an ITE for minimising the interference influences on the
protection level.
Coordination of SPDs respectively SPD-ITE
To ensure that two cascaded SPDs or an SPD and an ITE to be pro-
tected are coordinated during overvoltage conditions, the output
protective levels from the SPD 1 should not exceed the input resist-
ibility levels of SPD 2 or the ITE for all known and rated conditions.
Equipotential bonding between the surge protection
and the to be protected device
An effective voltage-limiting outcome requires a system-specific
observation which has to consider various conditions between the
protective device and the ITE.
Additional measures:
• Do not run the cable to the protected port together with the cable
to the unprotected port
• Do not run the cable to the protected port together with the earth
conductor (p)
• The connection of the protected side of the SPDs to the ITE to be
protected should be made as short as possible, or shielded
o Adherence to IEC 61643-22 will prevent severe damage.
o The need for protective measures for IT systems should
be based on risk assessment.
o Protection devices should be applied in a cascade ar-
rangement at the zone interfaces.
Electricity+Control
January ‘15
20