Can I select a breaker considering rated voltage and maximum current flow only? What are the other specification needs to consider? Do I have to consider Short time withstand current also. If so How to calculate it?

Most manufacturers of breaker do provide the guide for selection of breakers. You can look up their websites or get in touch with their marketing offices near you.

Regards
Chris Chew

Temperature factor is also a paramount factor.

Chris

Please any info link to manufacturers site? I think it will help.


Regards

Sam

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samchinnus

You need to consider following for breaker selection:
1. Rated continous current 2. Rated Voltage 3. Frequency (because it will tell you how fast breaker action you need?) 4. The Symmetrical & Asymmetrical short circuit current. 5. Peak make & break currents 6. Ambient teperature where you need to install breaker 7. the Recovery Voltage (if HV breaker is to be selected) 8.IP rating required etc

You can calculate the short circuit currents using any modern software that will automatically follow IEC and/or ANSI standards as you selected for your calculations.

Once you get above basic data for the system where breaker is to be connected then decide the type of CB you need that is SF6, Vaccum, ACB etc. After that you can look into manufacturers catalogs to select the best model that meet requirements.

Hope this clarifies.

Musa

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Musa Shah

I have listed below some websites on the topic.

http://www.abb.com/cawp/seitp2...1212F008D6C1257131005

http://www.electrical-installa...hneider-electric.com/

http://www2.sea.siemens.com/Pr...ical_Publications.htm

To search for more simply type 'selection of circuit breakers' in any browser.

Regards
Chris Chew

Calculate how much %dc your circuit breaker requires to break.This is one of the important aspect.If circuit breaker opening time is too short it will encounter large DC component stressing it.As opening time gets delayed %dc get's reduced.

Capacitors connected like power factor correction capacitors require under rating of the circuit breaker.

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Best wishes & regards
N P NAIR, MSc (Engg), C Eng, FIE(I), MIEE,Sr MIEEE.

Please give an example of how to provide 'under rating' of a circuit breaker for a 3-phase 300kVAr power factor capacitor unit.

I calculated the maximum continuous line current of the capacitor is about 435A per line. Does it mean I can use a 400A circuit breaker rather than a 500A rated unit?

You would use the 500A or even a 630A MCCB, a rule of thumb when selecting PFC protection is twice the KVAr in amps 100KVAr-200A, 150KVAr-315A and so on.

Others may disagree.....

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James