main breaker tripping

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JES2727

Senior Member
Location
NJ
Last spring I was called about a problem with a main breaker tripping. It was in an unoccupied building that was previously used as a pharmaceutical research & manufacturing facility. One of the breakers in the main switchgear would occasionally trip for no apparent reason, and half the building would be in the dark. I checked for any obvious causes of the problem and found nothing. I walked through the facility and shed as much of the load as I could. For example, there was a small power conditioner that was buzzing like hell, so I shut it down. Turned off the disconnects for some high-tech research equipment. Pretty much left nothing on except lights and HVAC. About a week later I get the call, it tripped again. The breaker is a Westinghouse DSL-206, and I found an Amptector Tester in the maintenance office. I contacted the manufacturer and obtained the manual for the tester, as well as the curves for the breaker. None of this was really useful to me, as I have no experience with this type of stuff. In the past, once the wire is pulled and terminated, the tech shows up to set up the breaker. But now I'm working for myself, so here I am. Anyway, I plugged in the tester and went through the steps. I wrote the numbers down and looked at the curves. And the curves were exactly that: a page of curved lines and some numbers I couldn't read. I couldn't make heads or tails out of it, but I think my daughter would enjoy coloring them in. So I just tweaked all the settings on the breaker. Turned everything up one notch. Long delay, short delay, etc. I know thats not the right way to solve the problem, but the building is unoccupied and the owner doesn't care to call in a team of experts. He just needs to keep the power on so the mag locks stay energized. I checked the building every week for 8 weeks, and the breaker did not trip. Until this past Monday (four months later). Also, there is a digital IQ meter on the gear which shows an overvoltage alarm every time I go there. About 505 volts line to neutral. Any advice would be appreciated. Is my next step to contact the utility, tweak the breaker settings a little more, or swap out the breaker with the spare that happens to be in an adjacent cabinet?
Thanks,
John
 

hurk27

Senior Member
Re: main breaker tripping

Sounds like a bad neutral bond some where from the main service transformer XO connection to this switch gear, A loose connection could send the electronics in the breaker off scale causing the tripping. you will need to trace the neutral connection to the service point then have the POCO check there side. It can be a bad connection on buss bars within the equipment cabinets. can be a major pain to track down if not happing all the time. Look for signs of heating at connections.
The 505 volts to neutral doesn't make sense as on a 480 volt system the max it can read with a lost neutral should only be 480 volts.
 

George Stolz

Moderator
Staff member
Location
Windsor, CO NEC: 2017
Occupation
Service Manager
Re: main breaker tripping

Originally posted by hurk27:
The 505 volts to neutral doesn't make sense as on a 480 volt system the max it can read with a lost neutral should only be 480 volts.
But the utility voltage can be higher than 480 volts. At a lumber milling operation I was at once, the nominal voltage was 480 and the actual voltage was 499, with most of the equipment at rest.

Considering the line-to-neutral voltage was equal to the normal line-to-line voltage at the service, that narrows your problem down a bunch. As Wayne said, the connections and wiring between the service and utility transformer, or the transformer itself are at fault. Unless the system is a corner-grounded delta supply, in which case this reading would be perfectly normal. But that's not a common configuration.

If it is a normal 480/277 system, I hope any 277 loads that were connected are okay. :)
 

hurk27

Senior Member
Re: main breaker tripping

George, Yes primary voltage most often is higher than the secondary voltage, But to get the higher primary voltage on the secondary line and neutral terminals would alter physics as we know it. :D
 

JES2727

Senior Member
Location
NJ
Re: main breaker tripping

Well it looks like I've made a mistake. The meter shows an overvoltage of 505 volts phase to phase . I apologize for my error. Line to neutral voltage is about 293 volts. These are not steady voltage readings, just the display of the alarm conditions. The voltage has always been within normal parameters when I've been present at the site.
I have found some of my notes from the breaker test I did. Here's what I have, though they don't mean much to me right now as I don't have the manual with me.
I think these are settings :
I-n : 800
I-s : 800
I n/s : 1
I pu : 5
Test results:
Long delay P/U : A - 4.9, B - 5.5, C - 4.7
Short delay P/U : did not trip
Ground fault P/U : 3.3A, which I calculated to be equivalent to 528. The ground fault setting was on "D" (320).
These results might be total nonsense, as I was pretty much guessing my way through the whole process, and my notes are not very thorough, but thanks for any help.
I am leaving in the morning for Pennsylvania ( deer season opens on Monday). When I return I will revisit the site and write down the meter readings, and see about checking the incoming connections. I'm sure I will be getting plenty of pressure to get this resolved. Thanks to everyone for the advice.

John
 

George Stolz

Moderator
Staff member
Location
Windsor, CO NEC: 2017
Occupation
Service Manager
Re: main breaker tripping

Originally posted by hurk27:
George, Yes primary voltage most often is higher than the secondary voltage...
When were we discussing that?

I said that in a nominal 480/277 system the actual voltage could readily be, as in this case, 505 volts line to line. For him to get that reading line-to-neutral (as I kinda suspected wasn't the case), that would involve misconnections (either by man or natural deterioration) solely on the secondary side of the transformer, perhaps including the transformer itself.

The primary is more than a couple thousand volts in this case.
 

George Stolz

Moderator
Staff member
Location
Windsor, CO NEC: 2017
Occupation
Service Manager
Re: main breaker tripping

Originally posted by hurk27:
The 505 volts to neutral doesn't make sense as on a 480 volt system the max it can read with a lost neutral should only be 480 volts.
Originally posted by georgestolz:
But the utility voltage can be higher than 480 volts
George, Yes primary voltage most often is higher than the secondary voltage, But to get the higher primary voltage on the secondary line and neutral terminals would alter physics as we know it.
Okay, I get what you were thinking. I may be dumb, but do you think I am that dumb? :(

I guess I should have worded it "But the voltage the utility supplies to the service normally can be higher than 480 volts."

Edit to add:

I remember that 499 volt event explicitly, which is why I chimed in. It was funny, because my boss asked if I had a meter handy, and I handed him my $10 special with "500VAC" on the dial. He looked at it, and handed it back, saying "The voltage here is really close to 500 volts, it could be over right now. I don't want to fry your meter." And then I joked with him that he was jealous that my "high" earnings were being spent on such expensive equipment. :D

Can you appreciate how bizarre, what a combination of events and resistances would have to intersect to create a line-to-line voltage from a regularly grounded 3? system with an open neutral? I can only comprehend the way single-phase open neutrals behave, I can only guess that 3? would be an act of Algebra I am not worthy to even guess at. But for a single-phase service to display these symptoms:

1. There would have to be basically no loads connected on one phase, and many connected on the other.

2. He would have had to take a reading from solely the overvoltage phase and not the zero-voltage phase to not immediately see this data and report it - it would be the highlight of the post, not the tripping.

[ November 26, 2005, 11:07 AM: Message edited by: georgestolz ]
 

jbwhite

Senior Member
Re: main breaker tripping

a long time ago i was working on a building under construction. the hvac tech told me that the supply voltage to the building was too high, causing his equipment to not work properly.

i called the utility and they came out to look. the tech told me that they had tapped the transformer based on the intended use of the building, and that because the building was not under full load at the time, the higher readings were normal.

the L to L voltage was between 504 and 508 at this time. averaging that on a 480v system and they were still within thier 5% rule for within tolerance.

after the building was under load i checked again and sure enough the readings were closer to 490.
 

hurk27

Senior Member
Re: main breaker tripping

BY George: Okay, I get what you were thinking. I may be dumb, but do you think I am that dumb?
Never George. :)

I was just pointing out that having that high of a reading between the line and neutral conductors would almost be impossible to be from the primary side of the transformer.
To many coincidence would have to take place to make it happen, As we found out it was a line to line reading, which would not be to out of the normal if the service transformers was high taped to adjust for voltage drop,
and at some time the load dropped off which will cause the voltage to rise to the set tap max level. This is more of what I think he's seeing and may need to contact the POCO to see if they can lower the tap if they don't plan to have the original load that the service was set for. as far as the breaker tripping? I'm not sure, not enough info.

[ November 27, 2005, 02:12 AM: Message edited by: hurk27 ]
 

zog

Senior Member
Location
Charlotte, NC
Re: main breaker tripping

JES2727 - OK those are you pickups but what were the delays? How much current were you using for each test, what were the delay settings on the breaker and how long did each test take to trip?
 

pwhite

Senior Member
Re: main breaker tripping

i worked for a pronting company years ago and we had a similar experience.

the main breaker tripped and shut the plsnt down.
the main would not reset.

we finally turned off the 2 breakers after the main and was able to reset the main.
we then turned on 1 of the 2 breakers and nothing happened. the 2nd breaker tripped the main.

there were 7 sub breakers. and we located the breaker creating the problem.

we kept dividing the circuits and found a line wire cut almost on half. we repaired it and got the plant up and running.

the senior electrician said the plant was not grounded properly.

i was just out of school and was in maintenance.

hope this trouble shooting method helps.

p white
 

ashtrak

Senior Member
Location
Maryland
Re: main breaker tripping

Have had a similar problem with a main breaker at one of our Rail Road maint. bases.(Westinghouse breaker, 400 amp.After repeated outages and resets, much trouble shooting, etc., etc., opening of manhole covers, a lot of meggering,input from everyone within a hundred mile radius,we discovered the breaker lug was loose on the breaker. Just a thought.
 

charlie tuna

Senior Member
Location
Florida
Re: main breaker tripping

i had a westinghouse breaker feeding an elevator machine room--think it was a 400 amp--- the normal load never exceeded 200 amps and it would just trip about every three or four weeks --different times of the day or night??? first call i installed a data logger and found out it tripped at a time when the voltage and amperage were normal. our spec for power company power is 10 per cent --so the high end would be 528 volts and the low end was 432 volts. during a infrared scan we found a bad contact in the transfer which feeds the breaker and thought that was the problem. but after a few months, it tripped!!! i ordered a new trip unit from westinghouse and replaced it ---nope ---tripped again. repaced breaker and reused new trip unity---no more problems-------been a year now---no trips!!! westinghouse!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
 

JES2727

Senior Member
Location
NJ
Re: main breaker tripping

The consensus here seems to confirm my suspicions : the problem could be just about anything! Thanks everyone for the replies, and thanks Zog for trying to help me with my test results. I can't find any more of my notes from the test I did.
Sounds like I should get my hands on some infrared test equipment and take a closer look at the connections. Or replace the breaker with the spare. This is one of those hard-to-solve problems that will probably continue to come back and bite me in the a## until I get it right.
 

nicknorth

Senior Member
Re: main breaker tripping

I had the excat same problem. I switched in the internal trip unit. I think the internal unit cost almost $1000 just for the part. I think the time we got done the company charge $2500.
 
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