When comparing switching devices, define the required circuit function before comparing ratings. Carrying current, switching loads, interrupting faults, isolation and earthing are different duties. Similar names or a shared interruption medium do not establish interchangeable functions.
Break the circuit duty into checkable requirements
Use the circuit diagram to assign normal operation, protective interruption, isolation and earthing to specific devices. Then connect control supplies, operating sequences and interlocks to those devices. A single product label should not stand in for the complete functional arrangement.
- Continuous current and specified load switching
- Protective initiation and fault interruption
- Isolation, earthing and position feedback
Distinguish breakers, load switches and contactors
Assess a breaker's required fault-interruption duty, a load switch's specified switching duties, and a contactor's load application and operating frequency. Vacuum describes an interruption technology; it does not independently identify the device class or establish a particular performance level.
- Assign duties to the complete model and configuration
- Distinguish electrical endurance from mechanical cycles
- Confirm protection and controls separately
Isolation, earthing and three positions are not breaking ratings
A disconnector needs a defined isolated state and permitted operating conditions. An earthing switch needs defined earthing, withstand and making duties. Three positions describe an arrangement: check each circuit connection and its interlocks rather than inferring fault-interruption capability.
- Review the primary connection at each position
- Record withstand and making duties separately
- Separate mechanisms from primary switching parts
Assign combination performance to the combination
Protection performance of a switch-fuse or contactor-fuse arrangement depends on its specific components and coordination. Compare replacement options across duties, interfaces, controls and verification scope, rather than using one interruption value as evidence of equivalence.
- List device, fuse and mechanism references
- Confirm protection coordination for the circuit
- Compare replacement differences item by item
Does the same current rating imply the same function?
A current rating does not establish interruption, isolation or earthing duties. Assess those functions separately.
Can making current be used as breaking current?
They describe different operations and conditions. Read each with its own definition and supporting test information.
Related selection resources
- Vacuum Circuit Breakers and Three-Position Switches
- Load Break Switches and Fuse Combinations
- Vacuum Contactors and Fuse Combinations
- Disconnectors, Earthing Switches and Accessories
- Distribution Reclosers and Load Break Switches
- Component Selection for Switchgear OEMs
- Transformer Protection Switching and Fuse Coordination
- Components for Medium-Voltage Motor Control
- Reading Switchgear Ratings and Test Data
- Switch-Fuse Combination RFQ Checklist
- Component and Complete-Switchgear Supply Scope
- Electrical Contacts
- Contact Arms
Build an enquiry around circuit duties
Provide the circuit diagram and intended device operations. Define load switching, protection, isolation and earthing before adding mounting and control interfaces.