Why do they both trip???

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winnie said:
Okay, really dumb question here: Are the breakers tripped, or are they off?

I mean do you know that the breakers are actually tripping, and not being flipped off by someone for unknown reasons?

-Jon
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When I have responded the breakers where in the intermediate tripped position.

However with these breakers that does not rule out someone push the 'Push to Trip' button located on the face of the breaker.
 
So, the breakers (so far) have never tripped while being monitored.

Is is possible to start keeping a written log of the trips? Track day, date, time, temp, humidity, etc., in order to look for a pattern. So far, your only pattern time wise is that the breakers have only tripped while not being monitored.

I think this is a surge event rather than a short circuit, but a surge could be caused by a temporary short circuit.

Surge events do strange things to OCPD's. I had one event at a die cast facility that took out about 50-60 fuses. The fuses ranged from 1 amp to 20, and one 400 amp. None of the fuses in the 30 to 300 amp range blew, and that included a 100 and a 150. We never found out what caused the surge, and every machine worked fine after the fuses were replaced.

Whist collecting info, one important piece would be as much info about the very first time this problem occurred.

Another approach would be to leave the monitoring device on, which would either cause the problem never to re-occur, or after several months or years you would finally get a reading pre-trip. :p
 
interrupting rating

interrupting rating

I have wondered ,but have not had the opportunity to look into it, when this happens ,are the panels series rated? Meaning , are the branch breaker's interrupting rating lower than the main breaker's interrupting rating?
 
B.Bray said:
I have wondered ,but have not had the opportunity to look into it, when this happens ,are the panels series rated? Meaning , are the branch breaker's interrupting rating lower than the main breaker's interrupting rating?
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That would only be an issue if the current was in the range of a bolted fault (e.g. there was some mis-wiring involved).
 
gar said:
170316-1713 EDT

This is one of those threads where there is insufficient information of the type needed to get a useful hint as to the cause. Fast response measurements need to be made that record data around the time of breaker tripping. Time correlation with what happens around the trip time is important.
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With all due respect to your abilities and knowledge this is not a fair criticism gar. We all come here with questions and are limited by our abilities, skills, knowledge and experience as well as the testing equipment we have access to and, just as importantly, understanding of.

iwire has said that there has been no tripping when power has been applied to the transformers. If power has been applied many times without tripping, then it is unlikely that transformer inrush is the cause of the breaker problem.
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No doubt, and no need for a super duper testing rig to come to that conclusion

On transformer inrush current. I have previously discussed this several times. Unless you have studied magnetic circuit theory, and the characteristics of various ferromagnetic materials, then you probably have no real understanding of what happens when voltage is applied to a transformer. The shape of the magnetization curve for the core material and how far up this curve it is driven in a normal cycle, the magnetization level at the time of turn off, the resultant residual magnetization, and the point in the voltage cycle when power is reapplied determines inrush current which is mostly of 1/2 cycle duration. But it does take many cycles to reach a steady state condition. But only that first half cycle is of significance relative to typical circuit protection,

For a view of transformer inrush current see my photos P6, P7, and P8 at http://beta-a2.com/EE-photos.html .

The transformer used in my experiment probably used a core material like U.S.S. Transformer 72-29 from circa 1950. More efficient transformers today are probably more square loop in shape and would have higher peak inrush currents.
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This is all good information but has no effect on what any of us working in the electrical field day to day has any control over. All of what you are talking about is the kind good work that is done by brilliant people who deserve a tip of the hat from those of us that work in the field. Without this kind of work thousands of us could not do our jobs safely and efficiently. I think this is true for most electricians and engineers. Further to that point, I could pursue a course of study that would increase my understanding of what is happening inside a transformer to the greatest understanding my intelligence can handle but that won't change anything inside of any transformer I work on when I go back to work on Monday.

I think instrumentation of the proper capability is needed to monitor the problem iwire has.
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He has been monitoring and testing and even using an outside testing company. Its not enough to set up some test equipment hoping to record the one moment when the problem occurs and continue that indefinitely. Few paying customers budget for that and even when they do they don't have the patience.
 
B.Bray said:
I have wondered ,but have not had the opportunity to look into it, when this happens ,are the panels series rated? Meaning , are the branch breaker's interrupting rating lower than the main breaker's interrupting rating?
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Like I mentioned a couple times already, those breakers with adjustable magnetic trip settings may very well be lower then the non adjustable breakers in the panel (main included here) when set at the lowest setting.

Interrupt rating does need to be greater then the available fault current, but that is so it don't blow up under a fault.

If you want the branch breaker(s) to trip before a main breaker, the trip curve of the instantaneous trip function is what needs looked into and select branch breakers or set adjustable ones to a level that trips faster then the main does under the same current conditions.
 
iwire said:
Here is the deal, for long time we have had a customer that has some breakers that have been tripping.

Here is the panel I am dealing with, it has a 200 amp main breaker at the top and down at the bottom you can see two - 3 pole breakers, a 70 and a 100.

The other night I went there and the 200 amp main, 100 amp feeder and 70 amp feeder were all in the tripped position.


One_zpsvjh8vrcb.jpg


Below is the main breaker.
Four_zpsbwpkkfce.jpg


Here are the two 3-pole breakers

Two_zpsocdl3rw0.jpg



The 200 amp breaker supplies the panel from an ATS right beside it. In turn the ATS is supplied from switch-gear very close by. I would say the supply is very stiff, over done in house engineering. (Not a complaint, just saying they use a lot more copper than is likely required)

The 100 amp breaker supplies a panel 400'-500' away in a separate structure. This is an underground run, around 500 Kcmil copper in PVC. The load in less than 20 amps on all three legs. The panel supplies LED egress and exit lighting, a fire alarm booster panel and other small loads.

The 70 amp breaker is the primary supplying a transformer directly above the panel, lets say 15' to 20' of conductor from breaker to transformer. I did not check but suspect the transformer is a 30-45 kVA unit. 480-208Y/120.


We all suspect the underground run is failing, each time there has been a trip over the course of maybe two years and five or six trips the ground has been wet or moist.

I did use a basic mega meter on it and it went to the end of the meters scale.

Monday night I am meeting a testing company on site to do some type of advanced testing on the conductors.

Now here is the real question I have.

Regardless of the fault being on the 100 amp breaker or the 70 amp breaker why are they both tripping?

I understand the main and one feeder going to the tripped position at the same time but why are two unrelated feeder breakers tripping at the same time?

This has happened each time, always both breakers tripped.

Grasping at straws while there the other night I decided to move one breaker away from the other on the thought one was somehow tripping the other?? Magnetic field?? Just the sharp rap of one breaker tripping causing the other to go??? I have no clue but I did move the breaker.

Anyone have some insight? A technical reason for this? Poltergeists?

Three_zps9weuzbeu.jpg
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I did not read all the replies so pls excuse me if someone already mentioned this
From what I see in the pics the instantaneous or STD dial ( bottom left corner) of all 3 breaker is set to minimum. This is unheard of in the real work and I would almost bet that the tripping is caused by the inrush currents of the loads cycling on and off
Crank that dial to 80 or 100% and I'll bet the problem disappears
If you are squeamish then hire a PE to do a coordinator study and he'll tell you the same thing
I was just on a trouble call last month for the exact same problem


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I was too late to edit this but meant " unheard of in the real world."
All breakers and protective relays are shipped out with all settings at minimum due to liability.
They are then suppose to be set according to the engineers Study during field startup when the breakers
are high current tested. A lot of testing companies dial down settings (they don't bring the proper size test set)in order to get them to trip on inst.; then FORGET to turn them back up:happysad:
 
ATSman said:
I did not read all the replies so pls excuse me if someone already mentioned this
From what I see in the pics the instantaneous or STD dial ( bottom left corner) of all 3 breaker is set to minimum. This is unheard of in the real work and I would almost bet that the tripping is caused by the inrush currents of the loads cycling on and off
Crank that dial to 80 or 100% and I'll bet the problem disappears
If you are squeamish then hire a PE to do a coordinator study and he'll tell you the same thing
I was just on a trouble call last month for the exact same problem


Sent from my iPhone using Tapatalk
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What you said has aready been mentioned, and it has been my though all along that those mag trip settings need adjustment, exactly where they should be set IDK, but I still think that is the problem. OP doesn't seem to want to do anything with that for liability reasons, so I guess they need to hire someone else to solve the problem?
 
mbrooke said:
Unless code specifically requires selective coordination nearly 100% of the time those dials are left as they were first received (being at minimum).
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Just a quick search:

http://forums.mikeholt.com/showthread.php?t=133840

http://www.eng-tips.com/viewthread.cfm?qid=266117

http://iaeimagazine.org/magazine/20...nation-for-critical-systems-per-the-2014-nec/

http://ecmweb.com/design/protective-device-coordination-study-part-1-3

Bottom Line: In my experience with electrical distribution systems, LV & MV it has always been a good engineering practice to have system coordination to localize a fault, regardless of what the code states. This results in the reduced risk in life safety and downtime $$$ to the customer.
And BTW, with the advent of all of these Arc Flash programs now being required by insurance companies (the ones that are forced to pay out after an accident) isn't a Power Systems, Coordination Study, updated Single Line Diagram required in order to paste those PPE stickers on equipment?
 
kwired said:
What you said has aready been mentioned, and it has been my though all along that those mag trip settings need adjustment, exactly where they should be set IDK, but I still think that is the problem. OP doesn't seem to want to do anything with that for liability reasons, so I guess they need to hire someone else to solve the problem?
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Yeah, being in the field engineering & testing business I can understand why people are reluctant to make any breaker setting changes without any direction from higher authority. To us this is an every day thing and after 47 yrs experience we are used to it and we have not been called on it as long as the breaker has been properly tested to trip at it's current amp setting and is functioning properly.
ZOG may be out there to reply??
 
Pg 6-47 https://www.geindustrial.com/catalog/buylog/06_BuyLog2013_MoldedCaseCircBrkrs.pdf

Instant trip setting range min/max ~300/1000%
do these have a thermal/toc element?

Current settings
200 590
100 295
70 ~340

the 70 likely trips on xfmr inrush, set it 9 x xfmr current 500 A, 700%
same for the 200 (plus other loads), set at 600% 1200 A
100, no idea, but setting at 600% or 600 A should be no issue

most i/t molded case don't get to the instant range 1000-1200 %
 
ATSman said:
I did not read all the replies so pls excuse me if someone already mentioned this
From what I see in the pics the instantaneous or STD dial ( bottom left corner) of all 3 breaker is set to minimum.
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It has been mentioned many times and that may well be the problem.

This is unheard of in the real work
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Say what?

We live in vastly different world then because at least 95% of the breakers I see like this with simple mag trip adjustments are set to minimum and they hold fine.

and I would almost bet that the tripping is caused by the inrush currents of the loads cycling on and off
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Take a look at the panel schedules, do you see a load that seems suspect to you?

The only cycling I know of is that some of the lighting circuits go one and off once in a 24 hour period.

Crank that dial to 80 or 100% and I'll bet the problem disappears
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My customer could just have their maintenance guy do my job then.
 
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ATSman said:
I was too late to edit this but meant " unheard of in the real world."
All breakers and protective relays are shipped out with all settings at minimum due to liability.
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For sure and that is the same reason the company I work for will not adjust them without engineering direction.

They are then suppose to be set according to the engineers Study during field startup when the breakers are high current tested.
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That would be idea but that simply does not happen on thousands of jobs.

A lot of testing companies dial down settings (they don't bring the proper size test set)in order to get them to trip on inst.; then FORGET to turn them back up:happysad:
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I have never run into this.
 
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