Model Specifications of Miniature Circuit Breakers
Miniature circuit breakers (MCBs) comply with the GB/T10963 standard and are designed for household and similar applications. They are suitable for environments with a pollution degree of 2 and have a rated current of up to 125A. MCBs are intended for non-professional use and do not require maintenance. Commonly, they are installed in home distribution boxes, where they are often referred to as “open spaces.”
The primary protection functions of miniature circuit breakers are overload and short-circuit protection. These devices safeguard electrical equipment in homes and similar locations by preventing damage due to excessive current. MCBs are available in configurations with 1, 2, 3, or 4 poles, each offering independent protection. Regardless of which phase in the circuit encounters a fault, the miniature circuit breaker will activate. Based on the type of instantaneous release, MCBs are categorized into B, C, and D types, each suitable for different types of loads. The rated current of an MCB is denoted by a combination of letters and numbers. For example, “C40” indicates a rated current of 40A with a “C” type instantaneous release.
Common Parameters on Miniature Circuit Breakers
Typical parameters indicated on the MCB case include:
- A: Rated current
- P: Number of poles
- Ue: Rated operational voltage
- Ui: Rated insulation voltage (V)
- Umax: Maximum operating voltage (V)
- Umin: Minimum operating voltage (V)
- Hz: Rated operating frequency
- Uimp: Rated impulse withstand voltage (kV)
- Icn: Rated short-circuit capacity (kA)
- Icu: Rated ultimate short-circuit breaking capacity (kA)
- Ics: Rated service short-circuit breaking capacity (A)
- Tripping characteristics: B, C, D, MA
Differences Between C-Type and D-Type Miniature Circuit Breakers
Miniature circuit breakers with leakage tripping accessories serve as common leakage protectors. Among MCB types, the C and D types are prevalent. These types differ in their short-circuit instantaneous tripping current, while their overload protection remains the same:
- C-Type: The magnetic tripping current ranges from 5 to 10 times the rated current (In), meaning tripping occurs when the current reaches 10 times the rated level, with an action time of ≤ 0.1 seconds. This type is suitable for protecting standard loads and lighting circuits and is commonly used in households.
- D-Type: The magnetic tripping current ranges from 10 to 20 times the rated current (In), meaning tripping occurs at 20 times the rated current, with an action time of ≤ 0.1 seconds. D-type breakers are suitable for protecting equipment with high inrush currents or loads with large starting currents, such as small motors.