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6.16 Contact service life of auxiliary and main contacts
SIRIUS - SIRIUS 3RT Contactors/Contactor assemblies
170 Manual, 09/2017, A5E03656507120A/RS-AE/006
Contact service life of the main contacts
The characteristic curves show the contact service life
of contactors when switching resistive and inductive
three-phase loads (AC-1 / AC-3) as a function of
breaking current and rated operational voltage. This
requires operating mechanisms that switch at
random, i.e. not synchronized with the phase angle of
the supply system.
The rated operational current I
e
in accordance with
utilization category AC-4 (breaking of 6 times the
rated operational current) is specified for a contact
service life of at least 200,000 operating cycles.
If a shorter contact service life is sufficient, the rated
operating current I
e
/AC-4 can be increased.
In the case of mixed operation, i.e. if normal switching
operation (breaking of rated operating current in
accordance with utilization category AC-3) is mixed
with occasional inching (breaking of the multiple rated
operating current in accordance with utilization
category AC-4), the service life of the contacts can be
calculated approximately with the following formula:
Characters in the equation:
• X: Contact service life for mixed operation in
operating cycles
• A: Contact service life for normal operation (I
a
= I
e
)
in operating cycles
• B: Contact service life for inching (I
a
= multiple of
I
e
) in operating cycles
• C: Proportion of inching operations as a
percentage of all operations
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