VCB and Load Switch Buying Guide | Ratings, Mechanism and Duty
1. Match the device to the fault level and load
Confirm the system voltage, the rated current and the fault level at the installation point. A vacuum breaker clears fault current, so its interrupting rating must exceed the calculated fault level. A load break switch only breaks load current, so it is chosen for the normal current and used with a fuse where fault protection is needed.
2. Choose a breaker or a load break switch
| Device | Breaks fault current | Typical use |
|---|---|---|
| VS1-12 vacuum breaker | Yes, with relay protection | Incoming, outgoing feeders and transformer protection |
| VIG(C)-12GD three-position | Yes, integrated isolating and earthing | Compact switchgear and RMU modules |
| FLN36-12 SF6 load break switch | No, load current only | Ring and transformer switching with a fuse |
| FKN12A / FKRN12A switch-fuse | Through the fuse | Small transformers and branch circuits |
Use a breaker where adjustable protection and fault clearing are needed. Use a load break switch with a fuse where the transformer is small and a simple, low-cost protection is acceptable.
3. Select fixed or withdrawable mounting
Withdrawable breakers sit on a truck that rolls out for service, which shortens downtime and gives a clear isolating gap. Fixed breakers are bolted in place and suit compact panels, ring main units and cost-sensitive projects. Confirm the panel interface, the truck travel and the test position before ordering a replacement breaker.
4. Specify the operating mechanism and control
Manual spring charging is the baseline. Motorised charging, shunt trip and closing coils, auxiliary contacts and anti-pumping allow remote operation and SCADA control. Confirm the control voltage, the DC supply, the number of auxiliary contacts and whether the mechanism needs a mechanical operations counter.
5. Confirm interlocks and the protection interface
The breaker must interlock with the panel earthing switch, the truck position and the cable compartment door. Confirm the trip circuit, the relay interface, the CT ratios and the test terminals. A breaker that trips correctly on the bench can still fail to protect if the relay wiring or the CT ratio is wrong.
6. RFQ checklist
- System voltage, rated current and fault level
- Breaker or load break switch, fuse rating if used
- Fixed or withdrawable mounting
- Manual or motorised mechanism, control voltage
- Relay, CT ratio and trip circuit
- Interlocks and panel interface
- Quantity, destination and delivery date
Send the single-line diagram and the panel interface drawing and the device can be confirmed in one round.
