Catalog LV 70 2011 - Low & Medium Voltage - Siemens

CD-K System — 25 ... 40 A
© Siemens AG 2011
Configuration information
■ Function
Short-circuit protection
The lengths of the CD busbar lines given in the guide value tables
on page 3/18 and 3/19 take into account only the rated current
of the connectable luminaires.
To determine the precise length of the busbar line, voltage drops
and short-circuit protection must be taken into account.
z
inc. inc. CD CD
z
Protective device
Incoming cable
CD system
NSV0_00032
Luminaire
x
Tap-off with cable
2 2
1 mm or 1.5 mm
3
Voltage drop ΔU
According to the technical literature, the voltage drop should lie
between 3 % and 5 % when the load is evenly split in light networks.
ΔU(%) =
ΔU (V)
U e (V) × 100%
With ΔU (V) according to page 3/21
Fault protection according to DIN VDE 0100 Part 410
Calculation of the current resulting in automatic interruption, taking
into account the incoming cable and the outgoing feeder.
I a =
U o
Z s
=
U o
Z Source + Z Inc + Z CD + Z Out
(A)
=
U o
Z Source + Z Inc × l Inc + Z CD × l CD + Z Out × l Out
(A)
with
I a = Current resulting in automatic interruption (A)
U o = Voltages to ground (V)
Z s = Fault loop impedance. Can be measured, calculated
(Ω)
or determined using the network
model.
Z Source = Source impedance (Ω)
l Inc = Single length of incoming supply cable (m)
l CD = Single length of CD system (m)
l Out = Length of outgoing feeder (m)
Z Inc = Loop impedance of incoming supply cable (Ω/m)
Z CD = Loop impedance of CD system (Ω/m)
Z Out = Loop impedance of outgoing feeder (Ω/m)
For example:
Z Inc = 22 × 10 -3 Ω/m at 2.5 mm 2
Z CD = 8.25 × 10 -3 Ω/m at CD 30 A
5.67 × 10 -3 Ω/m at CD 40 A
7.51 × 10 -3 Ω/m at CD 2 × 25 A
Z Out = 54 × 10 -3 Ω/m at 1 mm 2
Provided that the protective device is positioned immediately
upstream of the CD system feeder unit, Z Inc can be ignored.
The admissible opening delay is as specified in DIN VDE 0100
Part 430:
with
t = Admissible opening delay (s)
S = Smallest conductor cross-section (outgoing (mm 2 )
feeder) to be protected 1 mm 2 or 1.5 mm 2
I a = Current according to above calculation (A)
t =
S
I (s)
( ) 115 × 2
a
The total break time of the selected protective device must not
exceed the determined admissible opening delay and must not
be greater than 5 s.
3/20 Siemens LV 70 · 04/2011