Siemens SIMATIC S7 System Manual page 65

A summary of wiring rules for the S7-200 SMART CPUs, EMs, and SBs is shown below:
Table 3- 11 Wiring rules for S7-200 SMART CPUs, EMs, and SBs
Wiring rules for...
Connectible conductor cross-
sections for standard wires
Number of wires per connection 1 or combination of 2 wires up to 2 mm
Wire strip length
Tightening torque* (maximum)
Tool
* To avoid damaging the connector, be careful that you do not over-tighten the screws.
Note
Ferrules or end sleeves on stranded conductors reduce the risk of stray strands causing
short circuits. Ferrules longer than the recommended strip length should include an
insulating collar to prevent shorts due to side movement of conductors. Cross-sectional area
limits for bare conductors also apply to ferrules.
See also
General technical specifications (Page 679)
Guidelines for lamp loads
Lamp loads are damaging to relay contacts because of the high turn-on surge current. This
surge current will nominally be 10 to 15 times the steady state current for a tungsten lamp. A
replaceable interposing relay or surge limiter is recommended for lamp loads that will be
switched a large number of times during the lifetime of the application.
Guidelines for inductive loads
Use suppressor circuits with inductive loads to limit the voltage rise when a control output
turns off. Suppressor circuits protect your outputs from premature failure caused by the high
voltage transient that occurs when current flow through an inductive load is interrupted.
In addition, suppressor circuits limit the electrical noise generated when switching inductive
loads. High frequency noise from poorly suppressed inductive loads can disrupt the
operation of the PLC. Placing an external suppressor circuit so that it is electrically across
the load and physically located near the load is the most effective way to reduce electrical
noise.
S7-200 SMART DC outputs include internal suppressor circuits that are adequate for
inductive loads in most applications. Since S7-200 SMART relay output contacts can be
used to switch either a DC or an AC load, internal protection is not provided.
S7-200 SMART
System Manual, V2.3, 07/2017, A5E03822230-AF
CPU and EM connector
2 mm to 0.3 mm (14 AWG to 22 AWG)
2 2
(total)
6.4 mm
0.56 N-m (5 inch-pounds)
2.5 to 3.0 mm flathead screwdriver
SB connector
1.3 mm to 0.3 mm (16 AWG to 22 AWG)
2 2
1 or combination of 2 wires up to 1.3 mm
2
(total)
6.3 to 7 mm
0.33 N-m (3 inch-pounds)
2.0 to 2.5 mm flathead screwdriver
Installation
3.4 Wiring guidelines
2
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