How to Read MCB Nameplate Rating?

MCB (Miniature Circuit Breaker) is very common protection device (Such as fuse) used in domestic and Industrial application. It is very important device, which is to be procured with care.

But when we use to visit shops or take advice of our “expert” electrician then in most of time, without any technical consideration they advise for a particular brand. For us, especially who is not from electrical background, it is very tough to understand technical points of MCB.

We just see the MCB rating and buy it. It is really a wrong practice. Your electrician or shopkeeper may be suggesting you the right product but you also should know about it while purchasing.

Deciding MCB is very simple. Most of the data is generally printed on a MCB. Only few local companies hide information and you can easily ignore them. We would like to tell you about printed information of MCB.

How to read MCB Nameplate Rating
  1. Model Number.: All reputed manufacturer has a particular code of each device type. It will be very easy to communicate with seller or manufacturer, if you quote the model no., in case of any service complaint.
  2. MCB Current and Curve Rating: As shown in example, it is mentioned C20 (and in the below image, it is B25). First letter is showing the characteristics curve. There are three characteristics curves (In common use) available- B C & D. B curve indicates that short circuit rating of device is in range of 3-5 times of standard rated current (Which means, TIME for Trip initiation i.e. the less rating of the the time will be Fast acting, like for protecting sensitive Electronics devices and equipment). C curve indicates it to be 5-10 times and D curve indicates it to be 10-20 times. Be very careful while selecting this. On a resistive load (say heater, normal lighting load) it will B Curve, for inductive load (Like pump, Motors etc.) it will be C curve and for highly inductive or capacitive load it will be D curve. The numeral part indicates rating of MCB in Ampere. In the given example it is 20A. MCB rating is very important and be very precise about it.
  3. Operating Voltage: It is in Volts and is the operational voltage for which current rating is said. In three phase it is usually 400V or 415 V. For single phase it is 230V or 240V. Choose as per your application only.
  4. MCB Breaking Capacity: Breaking capacity can be defined as the maximum level of fault current which can be safely cleared. It is written as in numerals like in in example it is 10000. It means it 10000A = 10kA. Choose breaking capacity as per your fault level possible. Since it is the parameter which may increase or decrease the cost, so it should be properly decided. Breaking capacity should be higher than the possible fault level. For domestic application where fault level cannot be calculated easily, it advisable that go for a standard breaking capacity of 10kA which is easily available. Please note that this rating is mentioned as per testing made on basis of IS 60898. If it is for IEC60947-2 then it need to be mentioned separately.
  5. Energy Class: MCB normally work on current limiting feature. It means that it does not allow fault to get it’s peak and trip before that. But since there is some time consumed in tripping, fault current will create some energy which will exist in system. This energy is termed as let through energy. For efficient MCB operation it should be limited. On basis of amount of energy it is classified in class 1, class 2 and class 3. Here Class 3 is best which allows maximum 1.5L joule/second. This is being tested as per IS 60898.
  6. Status Indicator: It shows the ON-Off Indication while in operation. Never buy an MCB which don’t have clear status indicator because serious damage may be occurred with ON-OFF confusion of the device.
  7. Operation Symbol: This is always printed by any good manufacturer. This shows operation mechanism of MCB.
  8. Additional Relevant Information : Information like Impulse voltage, ISI marking etc are usually printed on side of MCB. However there are many parameters on which quality of MCB should be judged but aim of this blog is to make you aware of printed information on MCB.
  9. Catalog No: Most of the MCB manufactures put the catalog number of the MCB products. This code provide the overall information on the manufacture website such as MCB specification and Datasheet ect.

Asif Malik

A young Electrical Engineer having more than 5 years of experience in Electrical Power System, Construction and Execution of different projects, Project Management, Electrical Inspection. He is a article Writer as well on the different topic related to Electrical Engineering and Information Technology.

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