Overload Protection In The 24 V Output Circuit - Siemens PSU300B Manual

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9.4 Overload protection in the 24 V output circuit

9.4 Overload protection in the 24 V output circuit
If an overload occurs, the electronic current limiting function limits the
SITOP PSU300M/300B output current to a maximum value (see Section Technical data
(Page 39)). The output cables are protected against a thermal overload if they are
dimensioned corresponding to the maximum rms output current, or protected using
additional components (for example, miniature circuit breaker, fuses).
However, a load circuit that fails as a result of overload, for instance, should frequently be
reliably and quickly identified and specifically switched off before the power supply goes into
current-limiting mode (in current-limiting mode, the supply voltage would also be reduced for
all of the remaining 24 V loads).
The SITOP PSE200U selectivity module with 4 outputs (versions with adjustable output
current range for each output from 0.5 ... 3 A and 3 ... 10 A) is available; this monitors the
24 V branches for overload and short circuits (Figure 9-5 Selectivity module (Page 70)). Brief
current peaks, e.g. as a result of a high inrush current, are permitted, and branches with a
longer overload are switched into a no-current condition. This is also ensured for cables in a
high-ohmic condition and for short-circuits that slowly develop over time.
When an output fails, the fault is signaled using a group signal contact or as a single channel
signal, and the branch of the module involved is displayed using an LED.
For variants with single channel signaling, function blocks for evaluation purposes are
available for SIMATIC S7-1200/1500/300/400, for STEP 7 Classic and TIA Portal at no
charge.
You can find additional information at:
SITOP PSE200U selectivity module manuals
(http://support.automation.siemens.com/WW/view/en/10807226/130000)
Figure 9-5
70
Selectivity module
SITOP PSU300M/300B
Manual, 11.2014, C98130-A7574-A2-2-7629