Siemens SIMATIC ET 200SP Manual page 22

Wiring
3.3 Current transformer selection data
The following table shows the resistance values of copper cables for typical cross-sections
with ρ = 0.017857 Ω x mm
Estimating the length for a connection cable
The value in the table must be less than the calculated terminal resistance R
cable. For the resistance R
connection cable (outgoing and incoming line) with a length of 10 m from a cross-section of
0.75 mm
section
0.25 mm
0.34 mm
0.5 mm
0.75 mm
1.0 mm
1.5 mm
2.5 mm
Checking the ratio of burden load and power loss
The rated burden of the transformer must be 1.5 to 2 times greater than the power loss in the
connection circuit to ensure that the transformer is not overloaded and that the current
limitation is ensured during a short-circuit.
At a maximum secondary current of 4 A the power loss in the connection circuit is calculated
in accordance with the following formula for a connection cable (outgoing and incoming line)
with a length of 10 m and a cross-section of 1.0 mm
Meter of 25 mΩ:
The ratio of the rated burden and the power loss in the connection circuit thus amounts to:
The required ratio of rated burden and power loss in the connection circuit lies within the
required range. The transformer is dimensioned sufficiently large.
See also
Technical specifications (Page 66)
22
2
upward.
2
Cross- AWG
0.5 m
24 35.7 mΩ
2
22 26.3 mΩ
2
21 17.9 mΩ
2
19/20 11.9 mΩ
2
18 8.9 mΩ
2
16 6.0 mΩ
2
14 3.6 mΩ
2
/m
of 287.5 mΩ used in the above example it is possible to use a
Lmax
Cable overview for copper
1 m
71.4 mΩ 357.1 mΩ
52.5 mΩ 262.6 mΩ
35.7 mΩ 178.6 mΩ
23.8 mΩ 119.0 mΩ
17.9 mΩ 89.3 mΩ
11.9 mΩ 59.5 mΩ
7.1 mΩ 35.7 mΩ
Analog input module AI Energy Meter 400VAC ST (6ES7134-6PA01-0BD0)
5 m 10 m
714.3 mΩ
525.2 mΩ
357.1 mΩ
238.1 mΩ
178.6 mΩ
119.0 mΩ
71.4 mΩ
and a burden resistance of the Energy
2
Manual, 10/2017, A5E36061895-AB
of the
L max
50 m
3571.4 mΩ
2626.0 mΩ
1785.7 mΩ
1190.5 mΩ
892.9 mΩ
595.2 mΩ
357.1 mΩ