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When we design or build a electrical installation,we must know how to choose the suitable circuit breaker for the any application that we design. For electrician,this is compulsory knowledge. So here i want share my little knowledge about circuit breaker sizing method. This calculation for sizing the miniature circuit breaker. For that why i will discuss it in my next post…so this time i want explain the simple way how to sizing the miniature circuit breaker for our application.

Example : We want install 1 unit single phase motor. Power supply VAC,50 Hz. Refer the ampere rated in technical data for MCB from manufacture. It for general application and for small motor. Please refer the table below for MCB type for the application.

So…the conclusion from the calculation,we get the specification for MCB to install on our application For more detail,please contact the electrical engineer for their suggestion. This is a simple way how miniature circuit breaker sizing. Please refer the IEE manual for electrical guideline. As the starting current is not the same for DOL and star-delta starters can we use smaller MCB for star-delta starting?. U can use a smaller MCB but make sure it not below from the full load ampere rating.

For more safety about overload protection,we still have the overload relay :D. MCB will trip for inrush current.

Therefore the formula 1. Please elaborate. Please advice me. You can used isolator switch 40 ampere or 62 Ampere. It spare for future additional of mcb.October 4, 35 Comments. Some parameters are important but some parameters are confusing and mislead to wrong selection of MCCB. Some parameters are directly affected on cost of MCCB. D Accessories:. Filed under Uncategorized. About Jignesh. Parmar B. Tech Power System ControlB.

E Electrical. Membership No:M He is Presently associate with one of the leading business group as a Deputy Manager at Ahmedabad,India. Thank you, a very good clarification. Hi sir, Hope your doing good. Sir I have ordered your electrical notes and I have a question which is not cleared yet. On what basis the cable is selected? Please let me know with its Calculation and not by thumb rule. Thanks in advance.

mcb selection chart

Dear Sir, This article is so helpful and many thanks for sharing to enrich our knowledge. With best regards R S Babji Hyderabad.

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Hi Jignesh ,it was very useful and helpful note. Thanks a lot to share the such kind of information. It is the maximum possible fault current that the MCCB can clear.

If the fault current exceeds Ics value, the MCCB will be unable to trip and another protection mechanism must operate. If a fault above the Ics but below the Icu occurs, the MCCB can interrupt it successfully but will need a replacement due to the damage suffered.

Sir i confused with the above points in your article. Kindly clarify the main difference between Ics and Icu. Please clarify.

Icu Ultimate Braking Capacity means Circuit breaker can remove the fault and remain usable but Ics Service Braking Capacity means Circuit breaker can remove the fault, but it may not be usable afterward. Point 3 and 4 under Voltage related heading are having contradictory statements. Please rectify if this is still a live thread and post.

Ex 25hp 3p motor- what do i select current. Dear its good information. Please check and inform me if i wrong. You are commenting using your WordPress.

mcb selection chart

You are commenting using your Google account.How To Do. House Wiring Guide: Today we are going to discuss the house wiring. This article for those students who are interested to know about the house wiring. In this article, I will help you to understand how to select the rating of MCB, how to connect all loads of a house properly. In this article, the wiring diagram for a house which I have given is not proper as an electrical drawing. But the all the connections of the diagram are proper.

We know that when we apply for electricity, an energy meter is installed in our home by the electricity distribution company. After the energy meterwe need to wiring. First of all, we will do wiring in Rooms. I have explained the wiring of a single room. As you see in the above diagram the room has two lights, one fan.

Wiring Diagram for House with MCB Rating Selection Guide

A switchboard is used for distributing power. You can see the switchboard has three one-way switches, one two-way switch, one fan regulator, one five pin socket. The connection of neutral for all loads is connected by a common wire which is indicated by the Black color.

Mainly the wire of black color is used for the neutral connection. The connection of earth for all loads are also connected by a common wire which is indicated by the green color. Mainly the wire of green color is used for the earthing. According to the above diagram the light 1 is connected through a one-way switch. The Fan is connected through a one-way switch and a regulator.

A five pin socket is placed in the switchboard to connect the external temporary load. Read also:. Current calculation of the Room: The calculation of current is very important because the selection of MCB depends on it.

As you see in the above diagram, we assumed the light 1 draws 0. Also, assume the maximum 1 Amp load can be connected to the socket. So the total load of the room is 2 Amp. Now we discuss the power distribution from the energy meter to all rooms.

As you see in the below diagram, a two pole MCB is connected after the energy meter.Hi Jignesh, I am working in a project where there are 12 nos. There are LCS located near the motors.

MCB SELECTION CHART FOR APPLICANCES

Kindly advise some mitigation measures in this kind of situation to avoid mal-operation. Regards Debmalya. Would you like to send me a table for these symbol. I hope your reply soon.

How to select MCB / MCCB (Part:1)

Thanks and best regards. The Selection of MCCB spreadsheet I can not select more than sq mm cable sizeso please update this sheet for other size of cable. I have downloaded this excel worksheet but I cannot access to it as it is being protected by a password can I have the password so I can start to use this excel work sheet?

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mcb selection chart

More Information. Electrical Software. Related EEP's content with sponsored links. It helps you to shape up your technical skills in your everyday life as an electrical engineer.

Debmalya Dasgupta Sep 27, Abdelkawy Almasry Sep 26, Patrick Weerasinghe Feb 10, Edvard Nov 27, Leave a Comment Cancel Reply. Subscribe to Weekly Digest Get email alert whenever we publish new electrical guides and articles.

The content is copyrighted to EEP and may not be reproduced on other websites. Facebook Linkedin Linkedin Twitter.The general procedure for the selection of correctly rated circuit breaker follows the following scheme of seven major questions you should answer.

Will it be used for the protection of connecting leads, protection of installation, group-protection or motor protection? Select the appropriate circuit breaker typewith or without the thermal overload protection. Decide which type of protective characteristic cable or motor protection. Do the setting ranges of the thermal and the magnetic release cover the requirements of the particular application protection of transformer or generator?

The setting ranges of the various sizes of circuit breakers are overlapping. The cross-section of the connecting leads to the motors are to be selected on the basis of the current setting of the thermal overload release of the circuit breaker. Eventually, the maximum permissible length of the connection is to be considered shock hazard due to touch potential in the case of a short-circuit.

Standardized characteristics indicated on the rating plate of Compact NSX circuit breaker:. While choosing CBs rated voltage, current and short circuit capacity of the system is must. This is very important while choose main incomer called upstream. Sometimes in smaller circuts short circuit capacity lesser in downstream circuit compared to upstream to reduce cost.

Safer side short circuit capacity must be uniform all over circuit to avoid nuisance trip of main income. Could I choose or order a Circuit breaker without knowing the value of the Short Circuit current?

And after choosing, to receive a preselected Short Circuit current value information from the Breaker maker? Respected sir please upload techique for fault finding in panel circuit at site of work and repairing and connection diagrame of amp control panel with air circuit breaker. Hi James, just follow the manual and setting accordingly follow the nameplate of motor specification. Edvard, When selecting a circuit breaker, I suggest that we sometimes need to consider mechanical as well as electrical ratings.

For instance many breakers will hardly ever be switched in the absence of a faultbut others may need to be routinely operated, say, twice a day, and not all devices are designed for that level of usage. Search for:. Premium Membership. More Information. Selection of rated circuit breaker The general procedure for the selection of correctly rated circuit breaker follows the following scheme of seven major questions you should answer. Learn here. Related EEP's content with sponsored links.

It helps you to shape up your technical skills in your everyday life as an electrical engineer. Professional in AutoCAD programming. Leave a Comment Cancel Reply. Subscribe to Weekly Digest Get email alert whenever we publish new electrical guides and articles.

The content is copyrighted to EEP and may not be reproduced on other websites.

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Facebook Linkedin Linkedin Twitter.Then start dividing them into different electrical branches on the basis of your wire size calculations and cost effectiveness. Now the branch has current less than 6 amps, MCB required will be 6 amp. NC- Non continuous load -Loads which are switched not on for full day. C — Continuous load — Loads which are in work full day like fridge, ac etc. Result Will be. It is not chargeable.

mcb selection chart

For JOB Application, please mail at pratham gmail. I have a question to ask that to prepare a complete line diagram is main db is fix with mcb and from there to rccb is required? Thanks for the info, it is really helpful. Is it a 3 Phase Hot Water Generator? See, the current rating changes abruptly for three phase system. Your email address will not be published. Save my name, email, and website in this browser for the next time I comment. Skip to content. Example 01 For example, suppose one building has 07 rooms with following equipment in each room.

C of Non Continues Load. NC- Non continuous load -Loads which are switched not on for full day C — Continuous load — Loads which are in work full day like fridge, ac etc. For MCB class, refer table 2. Gopiraj For AC system. Leave a Reply Cancel reply Your email address will not be published.MCBs or Miniature Circuit Breakers are intended to give protection against overloads and short circuits, which can cause damage to cables and equipment. MCBs have current ratings 6A, 10A etc.

The first characteristic is the overload which is intended to prevent the accidental overloading of the cable in a no fault situation. The speed of the MCB tripping will vary with the degree of the overload. This is usually achieved by the use of a thermal device in the MCB. The second characteristic is the magnetic fault protection, which is intended to operate when the fault reaches a predetermined level and to trip the MCB within one tenth of a second.

The level of this magnetic trip gives the MCB its type characteristic as follows:. Apart from compliance with the Wiring Regulations, which is the subject of another sheet, the importance of the "types" is to ensure that the MCB does not give unwanted tripping when a device it is protecting is started up.

For instance, for electric motors or low voltage lighting the use of a type B MCB may give unwanted tripping and the choice of a type C MCB will probably solve the problem. In some instances the type D MCB may have to be selected but in this case it may be advisable to discuss with a qualified engineer before there may be other problems created. The third characteristic is the short circuit protection, which is intended to protect against heavy faults maybe in thousands of amps caused by short circuit faults.

The capability of the MCB to operate under these conditions gives its short circuit rating in kiloamps kA. In general for consumer units a 6kA fault level is adequate whereas for industrial boards 10kA fault capabilities or above may be required. Where normal resistive loads are being fed the type B characteristic may be sufficient but in many industrial application motors and special lighting and data equipment is being fed which may adversely affect the MCBs during starting and it will be necessary to use type C characteristic breakers.

How to Calculate Circuit-Breaker Rating -- Circuit breaker amp size

However, caution should be practised because the characteristics for these MCBs may make compliance with the Wiring Regulation difficult without a change in the specifications of the other equipment. Ohms Laws Calculator.

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The level of this magnetic trip gives the MCB its type characteristic as follows: Type B - trips between 3 and 5 time full load current Type C - trips between 5 and 10 times full load current Type D - trips between 10 and 20 times full load current Apart from compliance with the Wiring Regulations, which is the subject of another sheet, the importance of the "types" is to ensure that the MCB does not give unwanted tripping when a device it is protecting is started up.


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