Siemens Simatic ET 200SP Manual page 29

Wiring
3.3 Current transformer selection data
Maximum length of the connection cable
To avoid overloading or damaging the current transformer, the burden Z
data sheet of the current transformer (in VA) must not be exceeded. To prevent this being
exceeded, the entire burden resistance (consisting of the resistance of the connection cable
and the internal resistance of the AI Energy Meter HF (see figure below) must be below a
certain resistance value (depending on Z
Figure 3-2
The maximum value of the resistance of the connection cable is obtained with the following
formula:
R
L
Z
n
Figure 3-3
Based on the maximum cable resistance in ohms, you then calculate the maximum length of
the connection cable. To do this, check the data sheet of the connection cable you are using.
Note
The length of the connection cable (outwards and return) must not exceed the value of
200 meters.
28
Maximum length of the connection cable
Cable resistance in ohms
Rated burden current transformer in VA
Maximum value for the resistance of the connection cable
Analog input module AI Energy Meter 480VAC/CT HF (6ES7134-6PA00-0CU0)
and I ).
n max
I Secondary current of the current trans-
max
former
R Resistance of the AI Energy Meter HF
burden
(25 mΩ)
specified on the
n
Manual, 07/2018, A5E42674880-AA