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AA039
Associate

Join Date: Apr 2012
Posts: 37

Circuit Breaker Tripping

08/26/2012 2:24 AM

Dear All, We have an office feeding from breaker.last week it tripped. We checked the cable and found some damaging on one of the core. We repaired it but while repairing we got 15 V ac earthing in neutral and felt that. We checked the grounding and 15 V ac reduced to just 3 volts. We finally repaired the cable using LT kit. When we put the breaker ON it tripped again. Kindly give suggestions. The cable is 70 mm2 4 core and 100 A breaker is used to feed the office having some lighting and fans load. The cable is buried in the ground at the depth of 1 feet. Ur urgent response is needed.
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tcmtech
Guru

Join Date: Jun 2009
Location: South of Minot North Dakota
Posts: 8376
Good Answers: 775
#1

Re: Circuit Breaker tripping

08/26/2012 2:59 AM

It would appear that you have more than one short and damaged place in your cable.

If it was me I would unhook everything at the load end and see if it still trips the breaker. If so there is still a short circuit in the line set. If not you either have a overload someplace or a bad breaker that is weak.
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santosh zingurde
Associate

Join Date: Nov 2011
Location: mumbai
Posts: 28
#6
In reply to #1

Re: Circuit Breaker tripping

08/26/2012 11:09 PM

Additionally check IR value of circuit breaker itself.
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Circuit Breaker
Guru

Join Date: Jul 2006
Location: CA (Central Arkansas, USA)
Posts: 599
Good Answers: 10
#11
In reply to #1

Re: Circuit Breaker tripping

08/27/2012 5:56 PM

Or at least if there is any current flowing with the load end disconnected. That would lead me to recommending replacement of the cable. -- JHF

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Joshi
Guru

Join Date: Oct 2007
Location: India
Posts: 1246
Good Answers: 34
#2

Re: Circuit Breaker tripping

08/26/2012 3:08 AM

Obviously there is a short circuit somewhere post incoming feeder in your office. Isolate the live supply, megger all LT distribution points to various loads for short circuit. This is a job for the professionals. Caution is the watchword.
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engr.
Participant

Join Date: Jun 2012
Posts: 4
#3

Re: Circuit Breaker tripping

08/26/2012 6:14 AM

I suggest you close all the branch circuits and try to open the main which is 100A, and then open the branches one at a time, if you happen to open the branch that causes the tripping then thats it...BINGO...you now found the culprit....ELIMINATION METHOD....
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TonyS
Guru
United Kingdom - Member - New Member

Join Date: Aug 2010
Location: Resting under the Major Oak
Posts: 4347
Good Answers: 181
#4

Re: Circuit Breaker tripping

08/26/2012 6:59 AM

Buried at only one foot down the liable culprit will be mechanical damage. Happy digging!

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lyn
Guru

Join Date: Oct 2008
Posts: 42355
Good Answers: 1693
#5

Re: Circuit Breaker tripping

08/26/2012 10:05 AM

Hire a qualified electrician to find/fix the problem.

It sounds like you are qualified for something, but just not this.

So, send all the amateurs back to their real jobs, go back to your office and call a real electrician to come fix the problem.

The people who depend on the power, and your insurance carrier, will thank you.
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pnaban
Guru

Join Date: Jun 2010
Location: srilanka
Posts: 2725
Good Answers: 5
#7

Re: Circuit Breaker Tripping

08/26/2012 11:54 PM

Is there any indicator in the CB to see why it tripped-OC,SC,EF etc?. Did you megger the cable?. What is the type/amperes of load?.

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Anonymous Poster #1
#8

Re: Circuit Breaker Tripping

08/27/2012 2:03 AM

there is a short circuit somewhere post incoming feeder in your office. Isolate the live supply, megger all LT distribution points to various loads for short circuit. ans also checked insulation value of in coming cable.
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joseph sithole
Active Contributor

Join Date: Oct 2009
Posts: 24
#9

Re: Circuit Breaker Tripping

08/27/2012 2:16 AM

Disconnect load end then try to reset breaker, if it trips -Disconnect cable at both ends and check insulation resistance(phase-phase;phase-earth;phase-neutral) then use a cable fault locator to locate point of fault and repair.

JS
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brettj1au
Power-User

Join Date: Feb 2009
Posts: 176
Good Answers: 6
#10

Re: Circuit Breaker Tripping

08/27/2012 2:21 AM

Well if you have turned off all the circuits connected to this cable & there is no load on it & the breaker still trips then the cable is damaged in another place.

That being understood I don't know where you are in the world but in Australia minimum depth was 2 foot (we're metric now & it has been revised to only 50cm instead of 60cm) under the ground, so as another member said you are most likely to have damage to the cable in multiple places. What are the conditions that the cable was laid? is it directly in the ground or enclosed in conduit is it laid in a bed of sand?

If it is buried direct with no conduit or sand with rocks in the trench then as the dirt has compacted into the trench there is a possibility that the cable has been damaged. This would be even worse if it is in an area where vehicles can drive over the trench. Even if it is in conduit only 1 foot in the ground the rocks can easily damage the conduit & cable when vehicles drive across the trench.

I would suggest that you get the cable dug up & relay it in a manor that meets local regulations if it was originally laid to local regulations I would think that you should replace the cable bury it deeper in the ground with conduit with a bed of sand around the conduit.

I would strongly urge you to get a qualified electrician to do the work to the local regulations for everyones safety & to reduce the chances of this happening again
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Geoffrey36
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United Kingdom - Member - Not quite retired Member

Join Date: Aug 2012
Location: Up an araucaria araucana tree, South London, United Kingdom
Posts: 132
Good Answers: 7
#12

Re: Circuit Breaker Tripping

08/28/2012 7:53 AM

If we are talking about Earth Leakage protection, there used to be both Voltage and Current (Residual Current) Circuit breakers. The Voltage Sensitive type a) is prone to operate in the absence of fault when the distance to the earthed neutral point is great enough to create a detectable 'neutral' volt drop and b) is dangerous if the earth connection is lost.

Voltage Operated Circuit Breakers are obsolete and dangerous and should be replaced with Residual Current Circuit Breakers (RCCB) without delay.

To AA039: What type of breaker do you have installed?
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KWASI BIMPONG
Associate

Join Date: Jan 2012
Location: Tema
Posts: 25
#13

Re: Circuit Breaker Tripping

08/28/2012 4:30 PM

Fellow, i think you have more shorts. But i will suggest you go on by doing further checks such as

1 Meggering the cables to groung and phase to phase as well

2 Check if no part of the breaker is not grounding

3 Calibrate the breaker
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Users who posted comments:

Anonymous Poster (1); brettj1au (1); Circuit Breaker (1); engr. (1); Geoffrey36 (1); joseph sithole (1); Joshi (1); KWASI BIMPONG (1); lyn (1); pnaban (1); santosh zingurde (1); tcmtech (1); TonyS (1)

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