Phoenix Contact PSR-CT Series, Operating Instructions Manual, Page: 37 / 69

Electrical connection
108366_en_01 PHOENIX CONTACT
37 / 69
Example: determining the cable length
– Six switches in series are to be used.
– The cable length from the safety relay in the control cabinet to the last switch
(PSR-CT 6) is 40 m.
– The cable length between each individual switch is 20 m.
– The safety relay consumes 75 mA at each of the two safe inputs.
Figure 4-2 Switch chain with six PSR-CT safety switches
Determine the relevant values using the example table:
1. In column n , select the corresponding section.
– In this example, six switches.
2. In the selected section, search column i
out
for a current
≥
75 mA.
– In this example: 100 mA.
3. In the same line, read the maximum cable length from the last switch (PSR-CT 6) to the
controller from column l
1
.
– In this example: 50 m.
Result:
– With a length of 40 m, the desired cable length l
1
is lower than the permissible value in
Table 4-3.
– The total length of the switch chain l
target
is 140 m and therefore lower than the maxi-
mum value according to Table 4-2 (l
max
= 200 m for

20 switches).
The planned application in this format is operational.
PSR-CT 6 PSR-CT 5 PSR-CT 4 PSR-CT 3
l
1
= 40 m l
2
= 5 x 20 m
l
nom
= 140 m
l
n
= 20 m
i
out
= min. 75 mA
PSR-CT 2 PSR-CT 1
Phoenix Co
ntact Saf
ety R
ela
y