Figure 3-2: Contact Areas - Siemens sirius System Manual

Switching with auxil-
iary contacts (≤ 110 V
and ≤ 100 mA)
Cross-ribbing
Contact reliability of
the auxiliary contacts
Definition of switch
fault frequency H
F
SIRIUS System Manual
GWA 4NEB 430 0999-02b
The following applies to the contactors of the SIRIUS range:
If voltages ≤ 110 V and currents ≤ 100 mA are to be switched, the auxiliary
contacts of the 3RT1 contactors or the 3RH1 auxiliary contactors should be
used instead of the main contacts because of their contact reliability. This
comes from their high contact stability due, in particular, to the shape of the
contact pieces (cross-ribbing).
This ensures that the points of contact remain conductive in spite of surface
contamination and the effect of dust.
These auxiliary contacts are suitable for electronic circuits (programmable
controllers) with voltages > 17 V and currents in the milliampere range (test
circuit: 17 V, 5 mA).
Surface contamination is the most common cause of contact faults. Cross-
ribbing the contact areas is an extremely effective way of increasing contact
reliability. All the auxiliary contacts of the SIRIUS contactors have this fea-
ture.
The following illustration show you how cross-ribbing is particularly effective
against surface contamination due to the high number of contact areas and
high surface pressure:

Figure 3-2: Contact areas

The contact areas of the SIRIUS auxiliary contacts display a high degree of
contact reliability. Fault frequency rates of H
100 mill. operating cycles at 17 V, 1 mA) have been registered.
These values apply to auxiliary contacts that are either integrated in the con-
tactor housing or can be snapped on as auxiliary switch blocks.
In the case of built-on auxiliary switch blocks at the side, fault frequency
-6
rates are between 10
The tests are based on the requirements placed on signal generators by
electronic controllers.
This means that with the auxiliary contacts of the SIRIUS contactors or aux-
iliary contactors, the permissible contact resistance is only exceeded once
8
during a total of 10 (100 million) switching operations. During a long period
of operation, therefore, a fault is not expected to occur, irrespective of the
number of switching operations.
A restriction applies in the case of auxiliary switch blocks built on at the
side.
The fault frequency H
during a certain number of switching operations.
Accumulated surface
contamination
Isolated contact areas
Here: 13 contact surfaces
Depression
Lip
-8
and 10 .
is defined as the number of contact faults that occur
F
3RT1/3RH1 contactors
-8
≤ 10
(i. e. < 1 fault per
F
3-15