SIEMIENS MCCB Series Short Circuit Rating Guide

SIEMIENS MCCB Series Short Circuit Rating Guide

Deep analysis of basic information

1.1 Core positioning

Siemens focuses on the application of "series short-circuit rating" for molded case circuit breakers (MCCBs) and matching fuses. Its core goal is to provide CSA (Canadian Standards Association) certified compliant series combination solutions for distribution system design, installation, and operation personnel, solving the pain point of "insufficient branch circuit breaker breaking rating" in industrial and commercial distribution - by scientifically matching the main equipment (line side) and branch equipment (load side), while ensuring the reliability of system short-circuit protection, reducing the cost of branch equipment selection.

1.2 Scope and boundaries of application

Applicable products: Siemens' full range of molded case circuit breakers (such as QP/BQ/BL series, QPH/BQH/BLH series, ED4/ED6 series, etc.) and J/R/T/L matching fuses, covering three voltage levels: low voltage (240V), medium voltage (480V), and high voltage (600V).

Applicable scenarios: Industrial plants, commercial buildings, civil facilities, heavy machinery and other types of power distribution systems, especially suitable for circuit design with high short-circuit current but branch equipment does not need to withstand full fault current separately.

Exclusion scope: Main branch equipment combinations not explicitly listed, non Siemens original equipment, and applications beyond the voltage/current range indicated in the document are not applicable to this guideline solution.

1.3 Definition of Key Terms

Series Connected Short Circuit Rating: The maximum short-circuit breaking capacity certified by testing after the main equipment and branch equipment are connected in series. This value is allowed to be lower than the available fault current of the system, but it must meet the requirement of 'combined rated value ≤ main equipment rated value'.

Interrupting Rating: The maximum short-circuit current that the equipment can safely break independently. Circuit breakers default to a symmetrical current of 5000A rms, while fuses default to a symmetrical current of 10000A rms (with priority given to the values indicated on the equipment nameplate).

Load Side Circuit Breaker: including branch circuit breakers, branch line circuit breakers, built-in main circuit breakers, and remote main circuit breakers, which need to form a compliant series combination with the main equipment.

Core rules and general requirements

2.1 Basic principles of series combination

Mandatory certification requirement: All listed main branch equipment combinations must be CSA certified. In practical applications, it is prohibited to replace unverified models, otherwise it may result in the failure of short-circuit protection.

Rating limit: The breaking rating of the series combination shall not exceed the breaking rating of the line side equipment (main circuit breaker/fuse), and shall not exceed the short-circuit rating indicated on the equipment nameplate.

Voltage matching requirements: The voltage levels of the main equipment and branch equipment need to be adapted. For example, a 240V system cannot mix 480V equipment, and three-phase equipment (3P) needs to be matched with a three-phase circuit.

Requirements for pole number correspondence: The pole number of branch equipment (1P/2P/3P) should match the pole number and circuit type of the main equipment. 1P/2P equipment is used for single-phase circuits, and 3P equipment is used for three-phase circuits.

2.2 General Safety and Compliance Requirements

The installation of equipment should follow the specifications of the power distribution system, ensure firm wiring, good insulation, and avoid potential short circuit hazards.

The practical application of serial combination needs to be supplemented and verified based on the "CSA Certified Component Catalog" to confirm the latest compliance status of the combination.

The equipment nameplate should clearly indicate key information such as the rated breaking value, voltage, number of poles, and model. Regular checks should be conducted during operation and maintenance.

Detailed scheme for voltage classification levels

3.1 240V level

240V is the mainstream voltage level for civil and small commercial power distribution. The document provides two types of solutions: circuit breaker series connection and fuse series connection, covering four types of series rated values and the most diverse combination types.

3.1.1 Series combination of circuit breakers

Series rated value (A) Main circuit breaker core information Branch circuit breaker core information Applicable scenarios

22000 models: QPH/BQH/BLH, QNH/QNRH, EQ967 #/EQ968 #, etc

Maximum current: 70A (1P), 125A (2P), 100A (3P), 200A (2P), 225A (2P), 250A (2/3P)

Polarity: 1P/2P/3P

Voltage: 120/240V Model: QP/HQ/BL, QT, QPF/BQF/BLF, QE/BE/BLE, QAF/BAF, etc

Polarity: 1P/2P/3P

Current range: 15-20A, 15-30A, 15-50A, 15-60A, 15-70A, 15-125A

Voltage: 120V, 240V, 120/240V for residential power distribution, small commercial buildings (such as convenience stores and offices), small industrial equipment (such as small motors and pumps)