SIEMENS
3/127
Siemens IC 10 · 2017
Power Contactors for Switching Motors
SIRIUS 3RT12 and 3TF6 vacuum contactors
3
Contact endurance of the main contacts
The characteristic curves show the contact
endurance of the contactors when switching
resistive and inductive AC loads (AC-1/AC-3)
depending on the breaking current and rated
operational voltage. It is assumed that the oper-
ating mechanisms are switched randomly, i. e.
not synchronized with the phase angle of the
supply system.
The rated operational current
I
e
complies with
utilization category AC-4 (breaking 6 times the
rated operational current) and is intended for a
contact endurance of approximately 200 000
operating cycles.
If a shorter contact endurance is sufficient, the
rated operational current
I
e
/AC-4 can be
increased.
If the contacts are used for mixed operation
, i.e.
normal switching (breaking the rated operational
current according to utilization category AC-3) in
combination with intermittent inching (breaking
several times the rated operational current
according to utilization category AC-4), the con-
tact endurance can be calculated approximately
from the following equation:
Characters in the equation:
X
Contact endurance for mixed operation
in operating cycles
A
Contact endurance for normal operation
(
I
a
=
I
e
) in operating cycles
B
Contact endurance for inching
(
I
a
= multiple of
I
e
) in operating cycles
C
Inching operations as a percentage of total
switching operations
Vacuum contactors
Type
3TF68 and 3TF69
Size
14
X
A
1
C
100
-------
A
B
--
1
–
+
-------------------------------------------------
=
a
(A)
Operating cycles at
Contactor type
Breaking current
NSB0_00654b
3TF68
3TF69
200
400
4
000
2
000
1
000
600
6
000
10
8
6
4
2
10
8
6
4
2
10
8
6
4
2
10
8
6
4
2
10
7
6
5
4
3
6
4
2
10
8
6
4
2
10
8
6
4
2
10
8
6
4
2
10
6
5
4
3
8
6
4
2
10
8
6
4
2
10
8
6
4
2
10
8
6
4
2
10
6
5
4
3
10
8
6
4
2
10
8
6
4
2
10
8
6
4
2
10
8
6
4
2
7
6
5
4
100
690 V
500 V
400 V
230 V
© Siemens AG 2016