Siemens Simatic S7-400 - Manual (Page 34)

General Technical Specifications
1-6
S7-400, M7-400 Programmable Controllers Module Specifications
A5E00069467-07
cuULu requirements on hazardous location on the battery power supply for
CPUs
The power supply to the backup battery of a CPU must be via a non–incendive
plug. The figure below portrays the concept of such connection.
Battery or
Power supply unit CPU with connector
“ext. batt.”
Cc = Cable capacity
Lc = Cable inductance
Figure 1-1 Power supply to the backup battery
The following conditions apply to the performance characteristics of this
connection:
Voc (no load voltage) = 15V Vmax = 15V
Isc (short–circuit current )= 50 mA Imax = 50 mA
Ca = Battery capacity/ Ci = 25 nF maximum
power supply
La= Battery inductance/
Li = 2 mH maximum
power supply
The battery/power supply which supplies the non–ingnitable connection must have
the following values:
Battery/Power supply CPU iput “Ext. Batt.” incl. cabel
Voc ≤ Vmax (15V)
Isc ≤ Imax (50 mA)