# main breaker tripping



## BBQ (Nov 16, 2010)

Seeing as you already changed the breaker you know that it must be drawing more than 50 amps at times. 

So it seems like you may have an intermentent short or ground fault.


Is this a home?

Are underground runs part of it?


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## Split Bolt (Aug 30, 2010)

As BBQ said, there may be something drawing a lot more when you are not there. Or there could be a direct short causing the trip. Since you've already changed the breaker, that probably not it. For a 200A main to trip, I would look into a 240V load bucking phases. When the main trips, does another 2-pole breaker (or single-poles on different phases) trip as well?


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## whittom (Sep 20, 2010)

This is at my church. We have a 400 amp service. There is 2 200 amp HE panels. The other panel is working fine.


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## whittom (Sep 20, 2010)

No other breakers are tripping. Going right to the main breaker. GE panels


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## brian john (Mar 11, 2007)

Thermal issue?

Perform a Fall of Potential test (FOP)

Possibel that you had two defective CBs? (would be unusal)

Do you have a min-max amp clamp?


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## whittom (Sep 20, 2010)

Never heard of TOP test, what is that?


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## whittom (Sep 20, 2010)

I have a thermal meter. The A phase is reading 125 degree. B phase about 90 degree. I do have a clamp on amp meter. A phase pulling about. 45 amps. B phase about 50 amps


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## whittom (Sep 20, 2010)

Breakers at the top of B phase feel warm to the touch.


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## Tom45acp (Sep 6, 2011)

whittom said:


> I have a thermal meter. The A phase is reading 125 degree. B phase about 90 degree. I do have a clamp on amp meter. A phase pulling about. 45 amps. B phase about 50 amps


Did you look at the busbars when you changed the breaker? A loose bus connection or a bent stab would cause some heating and it could be your breaker is tripping due to the heat of a loose connection.


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## whittom (Sep 20, 2010)

I plan on taking some breakers out to examine the busbar next time I go to the church.


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## Zog (Apr 15, 2009)

whittom said:


> Never heard of TOP test, what is that?


He means a millivolt drop test. An alternative (However more dangerous because it is live) test to measuring contact resistance.


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## whittom (Sep 20, 2010)

I looked up FOP test. Same as a ground resistance test looks like to me. Never had to one of those in my 30 years of being a sparky.


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## T Healy (Aug 27, 2011)

Have you looked for loose connections, such as A/C compressor or anything that hasnt seen any maintenance in a while? Not much load on either phase.


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## Zog (Apr 15, 2009)

whittom said:


> I looked up FOP test. Same as a ground resistance test looks like to me. Never had to one of those in my 30 years of being a sparky.


That is because a FOP test is for ground resistance, like I said the correct term is mV drop.


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## whittom (Sep 20, 2010)

I will check for loose connections next time I get to the job. I just can't understand why the branch circuit breaker would not trip and go to the main breaker and trip it.


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## T Healy (Aug 27, 2011)

The main could have a lower instantaneous trip setting. That may cause it to trip first.


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## Bbsound (Dec 16, 2011)

A main reacting faster than a branch breaker is not that unusual at all.

That's not how it should be, but I have seen somebody working on a 277 ballast trip out an 800 amp main before.


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## brian john (Mar 11, 2007)

whittom said:


> Never heard of TOP test, what is that?


I have posted this before and too lazy to edit it down.


We are often called by electrical contractors to investigate why fuses are blowing or CBs are tripping. Many times the cause is a high resistance connections resulting in sufficient heat to effect the thermal element in the fuse or CB.

A simple method to isolate the high resistance connection and thus the source of the heat is the Fall of Potential Test Method, commonly referenced to as the FOP test. To perform this test, one simply needs a multimeter with a millivolt scale, and an amp clamp.

There needs to be a load on the device to be tested, preferably a balanced load or close to balanced load. In the case of a fused safety switch (FSS). One would measure current across all three phases, then measure from line to load of one pole/phase of the conductor strands (if exposed) for each pole of the FSS. If one phase has a higher that average millivolt measurement (actually the voltage drop across the device under test). Your next measurement would be from line conductor to line of the fuse, if all readings are close to equal move to the next components of the FSS, in this manner you an isolate the high resistance connection.

With an arranged outage repairs can be implemented and a repair FOP measurement taken to verify repairs.

Our thermographers perform this test as part of their IR Scan to isolate to high resistance issue. As sometimes it is not possible to determine from a picture if the issue is a CB connection to the bus or the CB. Additionally it is not feasible to use a DLRO (Digital Low Resistance Ohm Meter)/ Micro ohm-meter to take measurements on small CBs and FSS due to contact point spacing of the test instruments, so our technicians take pre-repair and post-repair measurement s to verify repairs.


An example we IR’d a 200 amp CB this weekend with 155 amps per phase (average), millivolt readings were 38mv, 91mv and 42 mv. The readings were taken from the bus stabs of the CB, negating any possible issue with the CB to bus connection or conductor termination connector to CB connection. B phase had an issue, when we replace the CB we will do further testing and open the CB to see if visual thermal damage has started.

This test can be performed on single pole CB, or any 3-pole devices, we have used this on 4000 amp bolted pressure switches.

As with any testing of exposed energized parts, all safety cautions must be observed, wearing of PPE, isolating the area to be worked in. One issue we have had over the years is customers taking FLASH photography as we are taking measurements. We no longer permit customers to take photos, without prior notice. This minimizes heart attacks.


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## nolabama (Oct 3, 2007)

T Healy said:


> The main could have a lower instantaneous trip setting. That may cause it to trip first.


I tripped a stove outlet once and shut down the main to a whole condo complex.


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## brian john (Mar 11, 2007)

Bbsound said:


> A main reacting faster than a branch breaker is not that unusual at all.
> 
> That's not how it should be, but I have seen somebody working on a 277 ballast trip out an 800 amp main before.


 

That is more than likely ground fault on the main (though not required at that amperage)

Worse case for a 20 amp CB would MIGHT BE 12-14 times (and I have never seen a 20 amp CB with 14X for instantaneous). At 14 that would be 280 amps. the lowest instantaneous setting for an 800 amp is 2X= 1600 amps, even if you had a setting of 1X =800 amps. Not likely the 20 amp could trip the CB.

Now ground fault relays come from 1 amp-1200 amp (standard GFP relay 100=1200 amps) and more feasible, this was the cause of the trip. Or an 800 with a defective trip unit or a defective 20 amp.


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## whittom (Sep 20, 2010)

I want to thank everybody who has responded to my problem with this issue. I hope I can return the favor to you guys someday.


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## brian john (Mar 11, 2007)

whittom said:


> I want to thank everybody who has responded to my problem with this issue. I hope I can return the favor to you guys someday.


 
Where are you in VA.?


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## Bbsound (Dec 16, 2011)

brian john said:


> That is more than likely ground fault on the main (though not required at that amperage)
> 
> Worse case for a 20 amp CB would MIGHT BE 12-14 times (and I have never seen a 20 amp CB with 14X for instantaneous). At 14 that would be 280 amps. the lowest instantaneous setting for an 800 amp is 2X= 1600 amps, even if you had a setting of 1X =800 amps. Not likely the 20 amp could trip the CB.
> 
> Now ground fault relays come from 1 amp-1200 amp (standard GFP relay 100=1200 amps) and more feasible, this was the cause of the trip. Or an 800 with a defective trip unit or a defective 20 amp.


I don't remember the details, but it was a Siemens, and all the dials on the trip pack were all the way down.


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## Bbsound (Dec 16, 2011)

brian john said:


> Where are you in VA.?


Yeah, where you at?


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## whittom (Sep 20, 2010)

I have a small Electrical Contracting buisness in Newport News, Va. I also work in Richmond Va with Dominion Power.


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## brian john (Mar 11, 2007)

bbsound said:


> yeah, where you at?


 
and you


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## DPshocknya (May 23, 2012)

How often does this happen? I would hang there for a while monitoring all possible scenarios. A/C with parking lot lights starting at the same time? check every branch circuit individualy for abnormal conditions. Two bad main breakers sounds very unlikely


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## whittom (Sep 20, 2010)

I was at church this weekend and the main breaker tripped twice. Once in the middle of the service. I went to the panel and put my clamp on meter on th B phase which was drawing 50 amps, while I was checking the amperage on B phase it tripped again. The main and 2 single pole breakers were warm to the touch.


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## Sparky J (May 17, 2011)

nolabama said:


> I tripped a stove outlet once and shut down the main to a whole condo complex.


It's funny I did this earlier today had a condo I a highrise where we were replacing old devices and I came across some colorful wiring. Thought I fixed it ended up popping the main breaker to the unit. Had to do the walk of shame to get the maintenance man to unlock the electric room.
Found out someone hit the BX with a cabinet screw.
Made for a fun afternoon.


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## Sparky J (May 17, 2011)

Whit it sounds like you may have answered your own question If the main and 2 others are warm. Or at least a good starting place.


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## brian john (Mar 11, 2007)

whittom said:


> I was at church this weekend and the main breaker tripped twice. Once in the middle of the service. I went to the panel and put my clamp on meter on th B phase which was drawing 50 amps, while I was checking the amperage on B phase it tripped again. The main and 2 single pole breakers were warm to the touch.


Perform the FOP/millivolt test.


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## Split Bolt (Aug 30, 2010)

I'm pushing my stack of chips in the pot and taking a stab. One of the 2-pole breakers at the top has gone bad over the years. (GE, after all!) That breaker feeds an AC condensing unit that is locking-up or something. Since the disconnect at the unit is not fusible, the breaker won't trip and the AC is trying to turn-on, the heat on the busbar (or the load, for that matter) is causing the main to trip.

Whittom, please let us know what you find-out!

Anybody else gonna try their luck?


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## Bbsound (Dec 16, 2011)

brian john said:


> and you


Based out of Norfolk
Serve Norfolk, Chesapeake, Virginia Beach, Primarily
Have been as far as Williamsburg, Smithfield for our regular national commercial service accounts


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## DPshocknya (May 23, 2012)

Start like sparkyj said


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## brian john (Mar 11, 2007)

Bbsound said:


> Based out of Norfolk
> Serve Norfolk, Chesapeake, Virginia Beach, Primarily
> Have been as far as Williamsburg, Smithfield for our regular national commercial service accounts


I am in Leesburg, but service primarily the Washington Metro area, though we have jobs in VA Beach, Harrisonburg, Richmond and points north and west.


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## DPshocknya (May 23, 2012)

it is so hard to say without being there.. hope you find it and i am curious of your solution


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## brian john (Mar 11, 2007)

DPshocknya said:


> it is so hard to say without being there.. hope you find it and i am curious of your solution


There are only a few things that can be causing this, with some basic testing this should be fairly simple to resolve.

Defective CB

Thermal Issue

Instantaneous over current issue (load or fault) If the fault is a load such as a compressor it may not be cycling all the time.


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## thoenew (Jan 17, 2012)

Apparently one of our customers has a 1000A breaker that is tripping when he runs a couple welders and the welders are fed from seperate sub panels.


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## brian john (Mar 11, 2007)

thoenew said:


> Apparently one of our customers has a 1000A breaker that is tripping when he runs a couple welders and the welders are fed from seperate sub panels.



480 VAC service?

How long has this been going on?

Does the swbd, have phase failure or GFP?

Does the CB have static trip OCP?


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## thoenew (Jan 17, 2012)

brian john said:


> 480 VAC service?
> 
> How long has this been going on?
> 
> ...


Yes, it's 480 VAC.

It is a ground fault breaker, per code. Has the digital readout and all the little dials.

My coworker was telling me about it and that we have to go and check it out. They installed it before I worked for them. 
I don't know much about it, although I am kind of excited to investigate.


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## brian john (Mar 11, 2007)

thoenew said:


> Yes, it's 480 VAC.
> 
> It is a ground fault breaker, per code. Has the digital readout and all the little dials.
> 
> ...


Get the make and manufacture along with settings. With a digital reading it sounds fairly new. Some older GFPs had issues with, loads that had voltage spikes as the GFP relay aged.

See if there is a phase failure or under voltage relay.


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## whittom (Sep 20, 2010)

This is 240 volt single phase 400 amp underground service with 2 200 amp panel. The panels are over 30 years old. I been going to church here for 20 years with no problems from these panels. I had to order the new main breaker online.


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## Zog (Apr 15, 2009)

brian john said:


> Get the make and manufacture along with settings. With a digital reading it sounds fairly new. Some older GFPs had issues with, loads that had voltage spikes as the GFP relay aged.
> 
> See if there is a phase failure or under voltage relay.


Also find out if it is a 3 or 4 wire GFP, unbalanced loads can cause false trips on 3 wire GFP's because they actually compare phase currents to sense GF's.


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## LARMGUY (Aug 22, 2010)

brian john said:


> One issue we have had over the years is customers taking FLASH photography as we are taking measurements. We no longer permit customers to take photos, without prior notice. This minimizes heart attacks.
> 
> __________________


 

:laughing: :laughing: 
God I hate that!


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