Circuit Breakers
Switches that automatically open on faults and can be reset — MCB, MCCB, ACB, VCB and SF6 breakers.
Intermediate
| Type | Typical use |
|---|---|
| MCB (miniature) | homes, up to ~125 A; trip curves B, C, D |
| MCCB (moulded case) | up to ~2500 A; adjustable trip |
| ACB (air) | LV main incomers, up to ~6300 A |
| VCB (vacuum) | 3.3–33 kV distribution |
| SF₆ | 66 kV to 765 kV transmission |
MCB curves: B trips at 3–5× rated current (lighting/resistive), C at 5–10× (general, small motors), D at 10–20× (transformers, large motors). MCBs combine a thermal (overload) and magnetic (short-circuit) trip.
Breaking an AC arc relies on extinguishing it at a current zero and preventing re-strike. SF₆ is an extremely potent greenhouse gas, so vacuum and alternative-gas breakers are increasingly preferred.
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