How to Read MCB Nameplate Data Rating Printed on It?

Electrical Technology

How to Read MCB Rating, Marking, and Labels?

The MCB (Miniature Circuit Breaker) is a commonly used protection device in domestic and industrial wiring. Similar to a fuse, it plays a crucial role in electrical safety. However, when purchasing an MCB, it’s important to exercise caution and make an informed choice.

Often, when we visit shops or seek advice from electricians, they recommend a particular brand without considering the technical aspects. For those of us who are not from an electrical background, understanding the technical specifications of an MCB can be challenging.

Many people simply look at the MCB’s rating and make a purchase, but this can be a mistake. While your electrician or shopkeeper may recommend the right product, it’s also important for you to have some understanding of what you’re buying.

It’s advisable to educate yourself about MCBs and their specifications before making a purchase to ensure you select the most suitable device for your needs.

Selecting a proper MCB is generally straightforward, as most of the necessary information is typically printed on the device. Only a few local companies might obscure this information, but you can usually ignore them. Let’s go over the printed information you’ll find on an MCB:

How to Read MCB Nameplate Data Rating Printed on It?

1. Manufacturer’s Name:

This indicates the company that produced the MCB. For example, Schneider, ABB, Eaton, Siemens, Legrand, and Hager etc.

2. Model Number:

All reputable manufacturers have a specific code for each device type. It makes communication with sellers or manufacturers easier, especially in the case of service complaints.

3. Tripping Curve:

The first letter in the rating (e.g., C20, B25, C63) indicates the characteristics curve or tripping curve of an MCB. There are three common curves: B, C, and D.

Choose the curve carefully based on your application. The numeral part indicates the rating of the MCB in amperes. For example, 20A means a 20-ampere rating.

4. Rated Current (In):

In is the maximum current the MCB can carry continuously without tripping. It’s measured in amperes (A).

Example: The numerical part of the B25 MCB indicates the maximum current rating that the MCB can safely handle is 25A. (As shown in above fig).

In the IEC (International Electrotechnical Commission) and NEC (National Electrical Code) standards, commonly available current ratings for MCBs include:

These ratings represent the maximum current that the MCB can safely carry continuously without tripping.

It is recommended to use 80% of the load on the rated breaker, meaning the breaker current rating should be 125% of the load circuit.

Example: a 20A breaker should be used for 16A load circuits. (See – How to Properly Size a Circuit Breaker?)

5. Operating Voltage (Ue):

The voltage rating is the maximum voltage at which the current rating is specified. For three-phase systems, it’s usually 400V or 415V. For single-phase systems, it’s 120V, 230V or 240V. Choose the rating according to your application’s voltage requirements.

Example: The operating voltage rating in the above fig is 230V AC.

6. Breaking Capacity (Icu or Icn):

Icu or Icn is the maximum fault current the MCB can safely clear. It is written in amperes, such as 10000 for 10kA. Choose the breaking capacity based on the possible fault level, ensuring it is higher than the expected fault level.

Example: The maximum short-circuit current in the MCB shown in the above figure is 10000A. This means the MCB can safely handle a fault current of up to 10kA.

7. Number of Poles:

MCBs can be single-pole, double-pole, or triple-pole, or four pole depending on the number of conductors they can interrupt.

Example: The MCB shown in the above figure is 2-pole. This means it can be used for 120V or 230V circuits using Phase and Neutral, or for 240V AC circuits using 2 Hot wires.

8. Short Circuit Protection:

Some MCBs indicate the type of short-circuit protection they provide (e.g., magnetic, thermal).

9. Energy Class:

MCBs limit fault current to prevent it from reaching its peak, but some energy is still generated. This energy, termed let-through energy, should be limited for efficient MCB operation. MCBs are classified into classes based on the amount of let-through energy. Class 3 allows a maximum of 1.5L joules/second.

10. Status Indicator:

A clear ON-OFF indicator is essential for safe operation. Never buy an MCB without a clear status indicator, as confusion can lead to serious damage.

11. Operation Symbol:

This symbol, printed by good manufacturers, illustrates the MCB’s operation mechanism.

12. Catalog Number:

Most MCB manufacturers include the catalog number of their products. This code provides overall information on the manufacturer’s website, such as MCB specifications and datasheets

13. Additional Relevant Information:

Information like impulse voltage, ISI marking, and wiring diagrams is usually printed on the side of the MCB. While there are many parameters to judge the quality of an MCB, this guide aims to make you aware of the printed information on an MCB.

14. Standards Compliance:

Look for markings indicating compliance with relevant standards (e.g., IEC, UL).

General MCB Rating, Marking, Labels & Specifications

Below is the typical 2-pole MCB nameplate rating data, which shows the most important information printed on it. These generally include:

Click image or open in a new tab to enlarge

MCB Rating Marking-Labels and Specification

Warning:

The placement of MCB data on the nameplate may vary according to the manufacturer’s convenience. The model numbers of each manufacturer are styled differently, and there is no standard format. However, the information is typically translated into easy words for easy understanding. For detailed and accurate information regarding MCB rating and nameplate details, refer to the datasheet provided by the manufacturer of the MCB(s).

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