Switching Motorized Loads - Siemens SIRIUS 3RT Manual

6.5

Switching motorized loads

Applications
The 3RT10 / 3RT20 3-pole motor contactors or the 3RT233.-.....-4AA0 / 3RT234.-.....-4AA0
4-pole motor contactors can be used for switching three-phase motors.
The main contacts of the 3RT10 / 3RT20 / 3RT233.-.....-4AA0 / 3RT234.-.....-
4AA0 contactors switch in air under atmospheric conditions.
In contrast to these contactor types, the contact gaps of the 3RT12 vacuum contactors are
contained in hermetically enclosed vacuum interrupters.
No open arc or arcing gases arise. A minimum clearance to the grounded parts is not
required.
The particular benefit of 3RT12 vacuum contactors is that their electrical endurance is at
least twice as long as that of 3RT10 contactors. The 3RT12 vacuum contactors are therefore
especially well suited to frequent switching (utilization category AC-3, AC-4) in inching /
mixed operation, e.g. in crane control systems.
Note
3RT12 vacuum contactors are fundamentally unsuitable for switching DC voltage.
The following graphic shows the cross-section of a vacuum interrupter.
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SIRIUS - SIRIUS 3RT Contactors/Contactor assemblies
Manual, 09/2017, A5E03656507120A/RS-AE/006
Fixed contact
Contacts
Arc chute
Ceramic insulator
Metal bellows
Locating bearing
Movable contact
Configuration
6.5 Switching motorized loads
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