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JYOTI BHUSHAN
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Explain The Fault Level And Braking Capacity Of Breaker

05/27/2011 1:13 PM

suppose short ckt level for plant is provided 40 KA. what will happen if i use 30 KA circuit breaker for protection? please explain what is the importance of breaking capacity of fuse as each fuse rated in terms of cut off current and breaking current..
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samsam_sam45
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#1

Re: explain the fault level and braking capacity of breaker...

05/27/2011 1:26 PM

My total running load is 1000A , What size do i select for Bus Bar rating

can you reply for this comment jyoti bhusan. please
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WJMFIRE
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#4
In reply to #1

Re: explain the fault level and braking capacity of breaker...

05/27/2011 4:10 PM

My total running load is 165 pounds. If I'm running with a beer, it jumps to 165 pounds, 12 ounces.

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lyn
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#5
In reply to #4

Re: explain the fault level and braking capacity of breaker...

05/27/2011 4:59 PM

CAUTION!

Never run with a full beer. The risk of foam increases exponentially with each step taken.
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JYOTI BHUSHAN
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#13
In reply to #1

Re: explain the fault level and braking capacity of breaker...

05/28/2011 1:50 PM

sorry, i cannot answer it..
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AHMAD REZA CHANGIZ
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#17
In reply to #13

Re: explain the fault level and braking capacity of breaker...

11/21/2012 5:01 AM

BREAKING CAPACITY IN BREAKERS IS SIGNIFICANT FACTOR.IT CAN DEFINE COST OF SWITCH.WHEN A FAULT OCCUR IN CIRCUIT, CAPABILITY OF SWITCH DURING OF SHORT CIRCUIT THAT ENABLE SWITCH TO BE STABLE WITHSTAND HIGH CURRENT AND MAKES IT TO BE ABLE FOR NEW COMMISSIONING DEPEND ON QUALITY OF CONTACTS AND STRUCTURE OF BODY ,DISTANCE BETWEEN CONDUCTORS AND INSULATORS.

REGARDS

CHANGIZ

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TonyS
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#2

Re: explain the fault level and braking capacity of breaker...

05/27/2011 1:43 PM

My god! The blind leading the blind!

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lyn
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#3
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Re: explain the fault level and braking capacity of breaker...

05/27/2011 1:59 PM

Scares me to think there are people out there like this.
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msamad
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#6

Re: Explain The Fault Level And Braking Capacity Of Breaker

05/27/2011 5:41 PM

Every short circuit interrupting device (such as breaker, fuse etc.) is rated for the short circuit capacity. When short circuit occurs and passes through the device, the device interrupts short circuit current by opening the circuit path. When the breaker opens or the fuse blows, there occurs tremendous arc within it and the severity of arc depends on the amount of short circuit current flowing through it. The interrupting device should be capable of extinguishing the arc. This is one of the main reasons the device is rated with the short circuit current. A breaker or fuse rated short circuit current of 30kA must be capable of extinguish the arc of 30kA current within the device and safely interrupt a short circuit current path but is not able to extinguish the arc of 40kA short circuit current. Now if you use a 30kA rated device in a system of 40kA short circuit level and the short circuit occurs, think what may happen. In this case, 40kA may flow through the device and it will not be able to extinguish the arc and open the short circuit path and there will be a severe disaster.

Hope it helps.

- MS

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lyn
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#7
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Re: Explain The Fault Level And Braking Capacity Of Breaker

05/27/2011 6:21 PM

Well put. I think the OP should now have a full understanding of the subject.
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JYOTI BHUSHAN
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#12
In reply to #6

Re: Explain The Fault Level And Braking Capacity Of Breaker

05/28/2011 6:42 AM

Thanks for answer...
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JRaef
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#8

Re: Explain The Fault Level And Braking Capacity Of Breaker

05/27/2011 7:07 PM

I think in the case of circuit breakers there is also the issue of the physical forces expressed on the mechanical components during the fault interruption. The higher the current, the higher the magnetic repulsion between phases and using a breaker rated for less than the Available Fault Current runs the risk of the breaker becoming shrapnel.That's no so much an issue with fuses.

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TonyS
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#9

Re: Explain The Fault Level And Braking Capacity Of Breaker

05/27/2011 8:16 PM

This is what happens

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kvsridhar
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#10

Re: Explain The Fault Level And Braking Capacity Of Breaker

05/27/2011 10:52 PM

The Fuse is a current-limiting device. It means that the short-circuit current is not allowed to reach its maximum value, the fuse cuts it off well before that. Something like this....

The system may have a fault level of 30 kA, but the fuse may cut-off at a much lower value.

Of course, if you use a 30kA fuse in a 40kA system, better go far away before something explodes !

Please get a good overview of fuse technology from this document:

cooper bussmann

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Tornado
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#11
In reply to #10

Re: Explain The Fault Level And Braking Capacity Of Breaker

05/28/2011 4:00 AM

Good reference. Cooper-Bussmann also has (or used to have) an excellent video on this. (Fuses feeding a bus-bar short circuit with a tiny puff of smoke, versus a two-pole circuit breaker feeding a 4-foot loop of nominal cable, and blowing across the room.)

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kvsridhar
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#14
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Re: Explain The Fault Level And Braking Capacity Of Breaker

05/29/2011 10:43 PM

i knew i had something, but for the life of me, couldn't find it in any of my hard disks. Then, voila ! searched for Ferraz, and here it is...similar to the one you mention, but from Ferraz Shawmut.

http://www.youtube.com/watch?v=qcB6CY90f5A

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Tornado
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#15
In reply to #14

Re: Explain The Fault Level And Braking Capacity Of Breaker

05/29/2011 11:09 PM

That's not the same video I was thinking of, but it covers the same idea just as well. Good find!

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JRaef
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#16

Re: Explain The Fault Level And Braking Capacity Of Breaker

05/30/2011 8:39 PM

This is what I was referring to when I said that the breakers can potentially explode if not rated for the available fault current.

Breaker explosion video

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Users who posted comments:

AHMAD REZA CHANGIZ (1); JRaef (2); JYOTI BHUSHAN (2); kvsridhar (2); lyn (3); msamad (1); samsam_sam45 (1); TonyS (2); Tornado (2); WJMFIRE (1)

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