WCW1 Series 2000A 3P Air Circuit Breaker

An ACB is a low-voltage circuit breaker designed for very high currents (typically 630 A to 6300 A) used as the main incoming or tie breaker in low-voltage switchgear. It makes, carries, and breaks normal load currents as well as short-circuit currents, and quenches the resulting arc in open air using arc chutes and splitter plates. Because of its high breaking capacity and adjustable protection, it is the central switching and protective device in a power distribution system.

An MCCB (Moulded Case Circuit Breaker) is typically rated up to about 1600 A in a sealed moulded enclosure with fixed or limited-adjustment protection, while an ACB is rated from 1600 A up to 6300 A or more, housed in an open metal frame, usually drawout, with a fully adjustable microprocessor trip unit, wide accessory range, and communication. ACBs also offer much higher short-time withstand and breaking capacity, easier maintenance, and downstream protection coordination (discrimination) that MCCBs cannot match at these current levels.

When the contacts open under short-circuit current, an electric arc forms between them; the ACB directs this arc into an arc chute made of parallel steel splitter plates, which cool, split, and stretch the arc so that it cannot re-strike at current zero. Atmospheric air is the quenching and insulating medium — no oil, vacuum bottle, or SF6 gas is required. This makes ACBs safe, maintenance-friendly, and suitable for indoor low-voltage switchgear up to around 1000 V.

The 2000 A is the rated current (In) of the breaker frame — the maximum continuous current the pole assembly can carry at rated ambient temperature without exceeding temperature rise limits. The actual trip setting can usually be adjusted down (e.g., 0.8 × In = 1600 A) via the electronic trip unit to match the installed load. The 2000 A frame size is a standard main-incoming rating for large commercial buildings, hospitals, and industrial plants.

"3P" means the breaker has three poles, one for each phase (L1, L2, L3), and is used on a three-phase three-wire system where the neutral is not switched by the breaker. The neutral is earthed separately in the switchgear and does not pass through the ACB. For four-wire systems requiring switched neutral or neutral protection, a 4P version is specified.

A drawout ACB sits on a withdrawable cradle (truck) inside the switchgear compartment and can be moved between connected, test, and isolated positions using a racking mechanism. This lets maintenance crews withdraw the breaker while the busbars remain live, providing visible isolation. A fixed (also called stationary) ACB is bolted directly to the busbars; to remove it the busbars must be de-energized. The drawout design is standard for main incoming breakers where continuity of supply is critical.

LSI stands for Long-time, Short-time, and Instantaneous protection — the three standard time-current curves of an ACB trip unit. Long-time provides overload protection (inversely delayed, like a thermal relay); Short-time provides coordination for downstream faults (definite delay with adjustable pickup, allowing downstream breakers to clear first); Instantaneous trips with no delay for severe short circuits (magnetic protection). Pickup currents and time delays are all adjustable on the electronic trip unit.

It is shipped as a drawout unit in a cradle bolted into a dedicated cubicle of a low-voltage switchboard (typically IP4X or higher), with the incoming busbars connected to the fixed contacts of the cradle and outgoing cables/bus ducts on the load side. Auxiliary power (typically 220 V or 110 V DC/AC) is connected for the closing spring motor, shunt trip, undervoltage release, and trip unit electronics. Installation, racking, and commissioning must be performed by trained switchgear technicians following the manufacturer's manual and local standards.

Low-voltage ACBs are designed, manufactured, and tested to IEC 60947-2 ("Low-voltage switchgear and controlgear — Circuit-breakers"), which defines rated operational voltage, rated current, short-time withstand current (Icw), ultimate service short-circuit breaking capacity (Icu/Ics), impulse withstand, and trip characteristics. Additional type tests cover making/breaking capacity, temperature rise, dielectric behavior, and endurance. CE marking indicates conformity with EU LVD and EMC requirements.

A 2000 A 3P ACB is used as the main incoming breaker on the secondary side of a transformer in large commercial buildings, hospitals, airports, shopping malls, and data centers, and as a tie breaker between bus sections in an industrial switchboard. It is also the main feeder for heavy manufacturing plants, water treatment pumping stations, and mining installations. Its role is to safely carry the total plant load and to clear upstream faults while selectively coordinating with downstream MCCBs and MCBs.