Circuit Breakers: MCB, MCCB and ACB Buying Guide

Start with the protected circuit

A circuit breaker is selected for a circuit and its fault conditions, not simply for the largest current printed on its label. Miniature circuit breakers (MCBs), molded case circuit breakers (MCCBs, also spelled moulded case) and air circuit breakers (ACBs) cover different construction and application needs. A distribution-board replacement and a main switchboard incomer require very different information from the buyer.

Build a complete specification

Record the operating voltage, AC or DC duty, frequency, rated current, number of poles and exact trip-unit reference. Distinguish the frame size from the installed trip rating. Ask the project engineer to confirm required breaking capacity at the actual system voltage and any coordination requirements. A kA value quoted at one voltage must not be carried across to another voltage without manufacturer data.

Check the complete assembly

Fixed, plug-in and withdrawable versions may have different mounting and connection arrangements. List terminals, phase barriers, auxiliary contacts, shunt releases, undervoltage releases and motor operators separately. State each control accessory voltage. A photograph of the installed breaker and its full nameplate often prevents a quotation for the correct family but the wrong configuration.

Buying for the United States or an international project

Ask for the certification required by the project and evidence for the exact catalog number. An IEC rating alone does not establish suitability for a US installation. Likewise, a familiar family name does not prove that a specific variant carries a required approval. AurFort can quote listed ABB and Schneider Electric references; submit Siemens references as sourcing enquiries.

RFQ checklist

Send the complete SKU, quantity, nameplate image, voltage, frequency, poles, trip-unit designation, mounting arrangement, accessories, required documentation and destination. Identify whether you require an exact replacement or an engineer-approved alternative. Do not approve a substitution on amperage alone.

Explore catalog references

Examples for product research; suitability and availability must be confirmed for your project.

• ABB 2CDS631031R0065 — BMS311B06
• ABB 2CDS631031R0105 — BMS311B10
• ABB 2CDS631031R0165 — BMS311B16

Manufacturer references

• ABB documentation: 2CDS631031R0065
• ABB documentation: 2CDS631031R0105
• ABB documentation: 2CDS631031R0165
• Schneider Electric Electrical Installation Guide

These AI-assisted purchasing guides use manufacturer references and catalog data. They are not installation instructions or a substitute for project-specific engineering approval.