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Siemens TX-I/O Engineering and installation guide CM110562en_13
Building Technologies Principles of electrical design 2019-05-15
10.5.1 Max. cable lengths for island bus
Capacitance of two-core cables depends on the following
(with decreasing importance)
– Material (dielectrical constant
ε
r),
the lower the better, values below 4.5 are OK
– Insulation thickness b (the thicker the better)
– conductor's diameter a (the thinner the better)
a
b
10562z116
Material
εr
PVC
4 ... 4.5
Polyethylene
2.4
Silicon
3.2
TPE (PETP)
3.3
Teflon
2.1
Nylon
3.5
Cable type
A) Round cable
Insulation
thickness b
Resulting
specific
capacitance
Max. length
Lmax for
island bus
AWG16
1.5 mm
2
≥ 0.6 mm < 100 nF/km 30 m
AWG14
2.5 mm
2
≥ 0.9 mm < 80 nF/km 50 m
Cable type
B) Coaxial cable *)
Specific capacitance required
for coax. cable
Max. length
Lmax for
island bus
– parallel to AWG16
– parallel to 1.5 mm
2
< 65 nF/km
< 60 nF/km
70 m
75 m
– parallel to AWG14
– parallel to 2.5 mm
2
< 50 nF/km
< 45 nF/km
90 m
100 m
C) Coaxial cable parallel to
coaxial cable
< 60 nF/km
Spec. resistance shield:
< 11 Ω/km
75 m
*) Coaxial cable: Thanks to better high frequency features, approx. 10% longer cables
than with round cable are admissible.
The CS conductor carries the highest loads. Therefore the current must be routed
via the cable shield (the shield of a coaxial cable has a higher cross-section than the
core).
The above values are based on an RG62 cable with a specific shield resistance of
11 Ω/km for the shield. For other cables, the max. length must be adapted
accordingly.
Coaxial cable
Spec. capacitance
Spec. resistance (shield)
RG62, diameter 6mm
43 nF/km
11 Ω/km
RG59
67 nF/km
7.8 Ω/km
TALASS BGAL C100
56 nF/km
18 Ω/km
Estimation of
capacitance
dielectrical constan
t
values
Max. cable lengths
Coaxial cable types
(examples):
.
.
.