Selection of the protection devices for the electrical installation is fundamental to reducing the problems caused by abnormal service conditions. ACB and MCCB both are used for the safe making and breaking of electrical systems. In principle, both serve the same purpose. But there are some differences between these two devices. Let’s have a look.
Differences between ACB and MCCB
MCCB and ACB are both circuit breakers for low voltage circuit protection, but they have the following differences.
Definition and duty
ACB stands for air circuit breaker and MCCB stands for molded case circuit breaker. Both devices protect circuits against excessive currents. (overload and short circuit) By using their handle, they can isolate the load from the power supply. MCCBs can be equipped with thermomagnetic or electronic releases but ACBs can be equipped with electronic releases.
MCCB’s long-delay tripping characteristics are typically fixed, and the ACB’s characteristics are adjustable. This is so the protective characteristics of the generator of a transformer can be achieved easily when using the ACB for a power breaker. When using MCCB for these types of applications, the protective characteristics can be attained easily by using an electronic MCCB that has variable long-delay tripping characteristics.
Instantaneous tripping characteristics of MCCB are fixed for compact models and adjustable for large models. The ACB’s characteristics are adjustable.
MCCBs can be equipped with thermomagnetic or electronic releases but ACBs can be equipped with electronic releases. ACBs are donated with more protection functions by using the advantage of advanced electronic releases.
MCCB is used for general wiring protection. It is not suitable for applications requiring frequent switching. Its total breaking time is short, and transient energy is small, so MCCB is suitable for protecting wiring and load devices.
ACB is used for generator and transformer protection in the main circuit. Its rated short-time current is high, so easy to structure a selective breaking system.
The size of an MCCB is smaller than ACB. Components with low weight and volume make life easy for users of MCCBs.
The current rating of the ACB is higher than the MCCB. MCCBs are generally produced up to 3200A, but ACBs are produced up to 6300A.
Location in the circuit
The short-time capacity of the ACB is high. It is easy to structure a selective breaking system and is suitable for applications as the main circuit breaker. ACBs are usually used on the upstream side of the circuit but MCCBs are used on load side control. Load-side switching operations are more frequent than upstream.
Price and market size
The price of MCCB is cheaper than ACB. But the market size of MCCB is larger than ACB.
ACBs and MCCBs are subjected to high currents; therefore, maintenance of them is critical for reliable operation. MCCB has a simple and safe structure that does not require maintenance or inspections. However, the ACB is designed with many updated parts and must be sufficiently serviced and inspected. Thus, MCCB is not suitable for applications intended for frequent short circuit interruption.
Every time current is interrupted by opening contacts, the arc is generated owing to current inertia. Since the arc is significantly harmful to the contacts and insulating materials, it must be immediately extinguished. ACB generates more electrical arc when switching. Because it generally carries large amounts of current. ACB and MCCB are equipped with an arc suppression chamber. If there is no pollution in arc exhaust parts and no other abnormality, the breaker can be re-used.
Din rail mounting
Some small MCCBs can be mounted on din rail. It is impossible to mount an ACB on a din rail. Because ACBs are heavy.
Magnetic only protection
Some types of MCCBs have only magnetic protection. This type of ACB is not available on the market. ACBs have thermal and magnetic protection.
Most ACBs have utilization category “B” but most MCCBs have utilization category “A”.