Breaker Sizing

Refer to the local Wiring Regulations applicable to the country of use.

In the absence of a local standard, use the Institution of Electrical Engineers' current edition of the Wiring Regulations applicable in the UK as a guide to good practice.

Incomming circuit breaker. Pls give some more in formation about: phase, rated current, protection type, voltage,etc.

i dont think all those info is required to get calculatation procedure, i have not ask for rating of breaker, what i want to know how to calculate not the resulte of calculation, any way the info is as below

phase :3

rated voltage: 440

rated frequency: 50 Hz

Rated current: 800 A

Thanx Mr. vinod

I appreciate ur effort to put the light from technical point of view and that's prove ur tecnitiality while other people just have an argument to kill the time. ur shareing of Knowledge will be gr8 help to me.

Is it clear you can not have MCB

The batter alternate is Air Circuit Breaker for the rating of 800 Amps.

nascon

Dear

As the breaker names indicate , The MCB is miniature Circuit Breaker., i.e breaking capacity limited for short circuit / fault level .

MCCB i.e Moulded case Circuit Breaker., not limited to miniature SC.

The MCB sizing is limited up to lower short circuit / fault level say @ 63 Amp., due to product designed limitation of short circuit level / fault current @ 10 KA recently available on request for 80 / 100 Amp.

The MCCB sizing for the fault level are for higher breaking capacity ., i.e short circuit for more than 10 KA and up to 143 KA amp rating up to 1600 Amp.

nascon

Dear

you are talking about difference B/W MCB and MCCB, but discussion is not intendent to that.

Dear

Breaker sizing , if not discreamination of falut ? not amp and SC ? what do youmean over all dimension?

nascon

dear

breaker sizing is not fault calculation but it definitely amps but not SC

Dear

You must know the basic, when you are sizing the breaker with Amp ., it is rate Amp. And, the said rated amp must withstand the required SC / Falut current for the system it is connected to.

Hope, you will understand the what the sizing of breaker means ?

nascon

exactly, now the question is if you are saying withstanding, then it is not only SC but also time which is relavent, am not sure about it.

What's the load on the circuit? FTLOG, without that all questions are meaningless!

What is the criteria in selecting ACB, MCCB, OCB, VCB etc. in both LT & HT distribution. In other words, how is the / in what basis the selction of breaker is made? can some one explain??

HT , two more type of breakers are available i.e MOCB (Minimum Oil Circuit Breaker ) and SF 6 (Sulphur Hexa Fluoride)

nascon

MCCB & ACB are used in LT side. MCCB for low rating (It is safe upto 400 Amp) & ACB for more than 400 Amp.

OCB: OCBs comes just above ACB for highier rating. Earlier days it was used both in LT & low level HT side. Later it was used only in low level HT side. But now days OCBs are slowly getting replaced by VCBs. This is because of OCBs need more maintenance, maintenance cost is high & not environment friendly.

VCB & SF6: These are used in HT side. They is more relaible & efficient. For some special applications like very high making & breaking currents, VCBs are also used in LT side.

Note: The above said are the classifications & some what related to selection also. Other than this, selection includes Breaking capacity, Short circuit current, Load current capacity, Earth leakage current level, No of poles required, Protections required, Voltage level etc.

Regards,

Vinod.P (Asst Mgr-Engg),

SCJPPL, HP,India.

Email Id- vinod29mar@gmail.com

thanks vinoth,

though it was posted long back, you have replied with some valuable datas.

For calculating Breaking capacity of CB downlaod excel base program from

www.jiguparmar.com

Superb website....hats off to you Jiguparmar.

Ok...having seen and studied the replies, may i mention that you need to look at circuit breakers in series mode...discrimination and cascading. An excellent paper on this is available from Schneider, please visit ...

http://www.schneider-electric.com/documents/technical-publications/en/shared/electrical-engineering/dependability-availability-safety/low-voltage-minus-1kv/ect167.pdf