Write the required operation before choosing the device
A circuit may need routine load switching, transformer energization, cable switching or automatic fault clearance. List the required operations and their frequency. A single rated-current number does not describe all these duties.
A load break switch is selected for its declared switching capabilities. A circuit-breaker proposal must also be matched to its specified fault-clearing and operating duties. Do not treat a short-circuit making or withstand rating as proof that a load switch can interrupt the same fault current.
IEC 62271-103 addresses applicable switches and switch-disconnectors, while IEC 62271-100 addresses AC circuit breakers. The distinction helps structure the specification; the actual declared capabilities and test scope of the offered device remain necessary. Switch scope and circuit-breaker scope.
Compare the functions on the same circuit
| Required duty | Question for the proposal | Evidence or interface needed |
|---|---|---|
| Normal load switching | Is the actual load type within the declared capability? | Relevant switching duty and limitations |
| Cable or reactive-load switching | What specific duty is required by the network? | Applicable device ratings and assessment |
| Fault making and carrying | What current and duration can be encountered? | Declared making and withstand requirements |
| Automatic fault clearance | Which device detects and interrupts the fault? | Complete protection and tripping arrangement |
| Isolation and earthing | How are the required functions provided? | Offered assembly description and instructions |
| Frequent operation | What operating duty is expected? | Suitable mechanism and maintenance provisions |
Neither solution should be chosen from a generic cheaper-versus-better comparison. The appropriate arrangement depends on the job assigned to that circuit and the connected protection system.
Make fault-clearing responsibility explicit
If a load-switch arrangement relies on fuses or an upstream breaker, identify the protection boundary and the relevant coordination review. Do not leave the fault-clearing role implied by the phrase protected feeder.
If a VCB is proposed, identify sensing, relay or release, trip energy and required external signals. A breaker component without the rest of the scheme is not a complete protection package. Transformer-specific switch-fuse selection can be reviewed separately from the general switching-duty comparison.
Example: a ring connection changes its role
Imagine a hypothetical ring-network position originally used for routine switching under a utility operating scheme. The project later requires local automatic fault clearance at that position. Keeping the original load-switch description may no longer define the necessary function.
The designer should revise the protection and switching requirements, then ask suppliers to propose a supported assembly. The answer may change the switching device, sensing and controls. This is a functional change to the circuit, not simply an upgrade to a larger ampere rating.
Ask for an assembly proposal with declared boundaries
Provide the network diagram, load types, required switching operations, fault-duty information and protection ownership. Ask each bidder to state which required operations its offer supports and which need another device or a revised scheme.
The RMU range and MV switchgear category are starting points for comparing complete panel configurations. They do not establish that every listed family uses the same switch or breaker, or that Jinxing supplies all independent LBS and VCB components.
Submit the duty schedule through the project enquiry page. Final device selection, assembly compatibility and supporting evidence require technical confirmation against the proposed project.