Applications
9.4 Overload protection in the 24 V output circuit
SITOP modular 1ph/2ph
62
Operating Instructions, 06.2014, C98130-A7548-A1-3-7629
9.4
Overload protection in the 24 V output circuit
If an overload occurs, the electronic current limiting function limits the SITOP modular output
current to a maximum value (refer to Chapter Technical data (Page 37)). 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 channels (versions with adjustable output
current range for each channel from 0.5-3 A and 3-10 A) is available; this monitors the 24 V
branches for overloading and short-circuiting (Figure 9-5 Electronic protection of 24 V loads
using the SITOP PSE200U selectivity module (Page 62)). 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 a channel 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 versions with single-channel signaling, function blocks for evaluation purposes are
available at no charge for SIMATIC S7-1200/1500/300/400, for STEP 7 and TIA Portal as
well as for SIMOTION CPUs and SIMOTION SCOUT.
You can find additional information at:
SITOP PSE200U selectivity module manuals
http://support.automation.siemens.com/WW/view/en/10807226/130000
Figure 9-5
Electronic protection of 24 V loads using the SITOP PSE200U selectivity module
