Is this standard still valid for use?

No, it has been superseded by IS/IEC 60898-1. This standard is for reference only for older installations.

What is the difference between a Type B and Type C MCB?

A Type B MCB trips at 3 to 5 times its rated current (In) and is for resistive loads. A Type C MCB trips at 5 to 10 times its rated current (In) and is for general purpose and inductive loads. (Ref: Tables 2 & 3)

What are the standard MCB current ratings as per this code?

0.5, 1, 2, 4, 6, 10, 13, 16, 20, 25, 32, 40, 50, and 63 Amperes. (Ref: Table 1)

What does the breaking capacity of an MCB signify?

It is the maximum prospective fault current the MCB can safely interrupt without being damaged. It must be higher than the fault level at the point of installation. (Ref: Clause 4.5)

IS 12640 Part 1

: 1988

Miniature circuit-breakers for overcurrent protection for household and similar installations - Part 1: Circuit-breakers for ac operation

SupersededEssentialSpecificationBIMMEP · Electrical Installations

Superseded by IS/IEC 60898 (Part 1):2002

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This standard specifies requirements for AC miniature circuit-breakers (MCBs) for overcurrent protection in household and similar electrical installations. It covers rated voltages up to 415V AC, rated currents up to 63A, and defines characteristics, construction, performance, and testing methods for Type B, C, and D MCBs.

Specifies requirements for Miniature Circuit Breakers (MCBs) for household and similar installations (still commonly referenced in older specifications).

Quick Reference Values

Standard rated voltage240/415 V AC

Standard rated currents0.5 A to 63 A

Instantaneous tripping current (Type B)3 to 5 times rated current (In)

Instantaneous tripping current (Type C)5 to 10 times rated current (In)

Instantaneous tripping current (Type D)10 to 20 times rated current (In)

Minimum rated short-circuit capacity (Icn)3000 A (3 kA)

Standard operating temperature-5 °C to +40 °C

Practical Notes

This standard has been superseded by IS/IEC 60898-1. All new designs, specifications, and procurement should refer to the latest version of the superseding standard.

The selection between Type B, C, and D MCBs is critical: 'B' for resistive loads (lighting), 'C' for general purpose/inductive loads (fans, motors), and 'D' for high inrush current loads (transformers).

The MCB's short-circuit breaking capacity (Icn, e.g., 6kA, 10kA) must be selected to be higher than the prospective fault current at its point of installation.