Siemens SIMATIC S7 System Manual page 67

Typical suppressor circuit for relay outputs that switch AC inductive loads
①
②
③
If you design your own suppressor circuit, the following table suggests resistor and capacitor
values for a range of AC loads. These values are based on calculations with ideal
component parameters. I rms in the table refers to the steady-state current of the load when
fully ON.
Table 3- 12
Conditions satisfied by the table values:
Maximum turn-off transition step < 500 V
Resistor peak voltage < 500 V
Capacitor peak voltage < 1250 V
Suppressor current < 8% of load current (50 Hz)
Suppressor current < 11% of load current (60 Hz)
Capacitor dV/dt < 2 V/μs
Capacitor pulse dissipation : ∫(dv/dt)
Resonant frequency < 300 Hz
Resistor power for 2 Hz max switching frequency
Power factor of 0.3 assumed for typical inductive load
S7-200 SMART
System Manual, V2.3, 07/2017, A5E03822230-AF
See table for C value
See table for R value
Output point
AC suppressor circuit resistor and capacitor values
Inductive load
I rms 230 V AC
Amps VA
0.02 4.6
0.05 11.5
0.1 23
0.2 46
0.5 115
1 230
2 460
Ensure that the working voltage of the metal oxide
varistor (MOV) is at least 20% greater than the nomi-
nal line voltage.
Choose pulse-rated, non-inductive resistors, and
capacitors recommended for pulse applications (typi-
cally metal film). Verify the components meet aver-
age power, peak power, and peak voltage
requirements.
120 V AC
VA Ω
2.4 15000
6 5600
12 2700
24 1500
60 560
120 270
240 150
dt < 10000 V /μs
2 2
Installation
3.4 Wiring guidelines
Suppressor values
Resistor Capacitor
W (power rating)
0.1
0.25
0.5
1
2.5
5
10
nF
15
470
100
150
470
1000
1500
67