Achievable Cable Length With The Lsn 0300 A - Bosch FPA-5000 Product Information

56 en | Installation/Configuration Notes
3.3

Achievable cable length with the LSN 0300 A

The usable cable length depends essentially on the resistance of the cable and the number
and current consumption of the network elements.
The way in which the elements are distributed locally on the bus also makes a difference.
The possible cable length can be estimated using the formula (1). This formula is also used in
the FSD (Fire System Designer) calculation program and assumes the critical application in
which all network elements are concentrated at the end of the bus line. As a result, the
calculated cable lengths are on the safe side. The diagrams on pages Page 57 and Page 58 can
be used to make a quick estimate.
L =
The following applies:
L = the cable length in [m] that is to be calculated,
U
0
U
End
q = cable cross section = 0.503 mm
n
E
ρ= specific resistance of copper = 0.0178 Ohm mm
R
FET
I
NE
I
trans
I
flash
For technical reasons the cable length must not exceed 1600 m. It should be remembered
that the non-electrically isolated lines running from network elements to, for example, all
FLM-420 series interface modules with optically unisolated inputs must not exceed a total of
500 m (1640 ft) and must be included within the maximum cable length of 1600 m (5249 ft).
Using the diagram for LSN classic
FET resistor = 0.7 Ohm, fire alarm cable with ∅ 0.8 mm
Example 1:
You want to know the maximum cable length for a given number of network elements and a
given current consumption (n
3 mA curve. Then from the point of intersection go horizontally to the left to the Y axis and
read off the maximum achievable cable length. In this example it is 840 m.
Example 2:
You want to know the maximum number of network elements for a given cable length and
average current consumption of the network elements. (L = 1000 m, I
from the Y axis at 1000, go horizontally across to the right as far as the 20 mA curve and then
from the point of intersection vertically down to the X axis. Read off the maximum number of
network elements, in this example it is 8.
F.01U.028.089 | 5.4 | 2009.08
º
q U − U − n
0 END
2 Ó (n
= bus voltage at the connection terminals = 30 Volt,
= bus end voltage = 15 Volt (must not fall below this limit!),
= number of elements,
= FET resistance = 0.7 Ohm (classic LSN element) or 0.35 Ohm (LSN
= average current consumption of elements in [A],
= transmission current = 0.012 A,
= flash current = 0.018 A
Product Information
À
Æ Æ É
⁄
× R n − 1
E FET E
× I + I + I
E NE
trans
2
(for cable ∅ 0.8 mm),
2
/m),
= 50, I = 3 mA). On the X axis, go vertically up at 50 until the
E NE
Modular Fire Panel
É
2 × I + I + I
NE trans flash
É
flash
improved
= 20 mA). Starting
NE
Bosch Sicherheitssysteme GmbH
(1)
½
Ã
),