Protection and control
Vacuum, air and moulded case circuit breakers
Medium voltage breakers that interrupt network faults and low voltage air and moulded case breakers that protect boards and feeders, including replacements for existing panels.
- Medium voltage standard
- IEC 62271-100AC circuit breakers above 1000 V
- Low voltage standard
- IEC 60947-2circuit breakers up to 1000 V AC or 1500 V DC
- Key ratings
- rated current and breaking capacitybreaking capacity set by the fault level
- Replacement
- retrofit or like for likecompatibility with the existing panel decides
A circuit breaker is specified by what it carries and what it must interrupt. The rated current comes from the circuit. The short circuit breaking capacity comes from the prospective fault level at the point of installation, which is why the transformer impedance and the upstream network matter to a breaker order.
At medium voltage, distribution breakers are specified by interrupting medium, vacuum or gas. Name the medium in your enquiry if the site standard requires one. At low voltage, air circuit breakers serve incomers and large feeders, and moulded case breakers serve smaller feeders.
Replacing a breaker in an existing panel is its own discipline. The new device has to fit the cradle, the interlocks and the secondary wiring of the old one, or come as a retrofit designed for that panel.
What gets specified
| Parameter | Typical options | What decides it |
|---|---|---|
| Voltage level | Medium voltage or low voltage | The circuit |
| Rated current | In A | The load or transformer on the circuit |
| Short circuit breaking capacity | In kA | The prospective fault level |
| Interrupting technology | Vacuum at medium voltage; air or moulded case at low voltage | Voltage and duty |
| Mounting | Fixed or withdrawable | The panel and the maintenance approach |
| Operating mechanism and auxiliaries | Spring mechanism, motor, shunt trip, undervoltage release | Control and interlocking |
| Protection | Integral trip unit, or an external relay | Voltage level and scheme |
| Replacement type | New panel, like for like, or retrofit | The existing installation |
Applicable standards
| Standard | What it covers |
|---|---|
| IEC 62271-100 | Medium voltage breakers above 1000 V, including their making and breaking tests |
| IEC 62271-1 | The ratings every medium voltage switching device shares |
| IEC 60947-2 | Air and moulded case breakers up to 1000 V AC or 1500 V DC |
For a breaker in an existing panel
| Document | What it settles |
|---|---|
| Retrofit or adaptation drawing | How the new breaker meets the old cradle, racking and interlocks |
| Secondary wiring comparison | Which control and auxiliary contacts change position or voltage |
What a circuit breaker request needs
- Medium or low voltage, and the rated current of the circuit
- The breaking capacity, from the prospective fault level where it will be installed
- Vacuum or gas at medium voltage; air or moulded case at low voltage
- Fixed or withdrawable, and the motor, shunt trip or undervoltage release wanted
- For a replacement: the panel maker and type, and the old breaker's nameplate