400A Main turns off by itself

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big john

Senior Member
Location
Portland, ME
Guys please. There is no one physically turning the breaker off.
What makes you say that?

I agree with many of the other posters here: Eliminate the human variable. You're still checking electrical things despite all your electrical tests coming up negative, and unless you've physically watched it turn itself off, there's a huge possibility a disgruntled employee is doing this.

You've done your due diligence testing all the electrical possibilities:
- You've ruled out defective breaker by replacing it.
- You've ruled out overcurrent with your power recorder.
- You've checked for wiring faults with a megger.
- The only thing you haven't done is look for hot-spots with IR, but there's nothing to suggest it might be necessary.

If the breaker is turning completely off and the OEM says that the breaker ain't designed to do that without human intervention, well....
 

brian john

Senior Member
Location
Leesburg, VA
I have talked to two other electrical testers that have tested more CB's than I have and both say that to be in the reset/off position from a trip is not something they have ever seen in all their years of testing.
 

kwired

Electron manager
Location
NE Nebraska
If the breaker is turning completely off and the OEM says that the breaker ain't designed to do that without human intervention, well....
But he never asked about divine intervention:)

I thought he did mention one of his last posts that he did personally witness it trip yesterday? Making this one even more mysterious at this point.
 

charlie b

Moderator
Staff member
Location
Seattle, WA
Occupation
Electrical Engineer
I remained there for another hour or so, then as I watched it, the 400A main again simply turned off by itself. Absolutely no one else in the room with me.
In case anyone missed this part.
Well, obviously RTL is doing it himself! :lol:

I would suggest taking one of the breakers that you had removed (during your three replacements) and have it tested. I would be curious to know how it behaves when you subject it to an overload. Does it go into the "Trip Free" position or to the "Off" position. Several members, and the manufacturer, have stated that the symptom being described is impossible. Yet the OP has personally witnessed it. That leaves us with the Sherlock Holmes statement, something to the effect of,
When you eliminate the impossible, whatever remains, however unlikely, must be the truth.
So then, what remains? All I can offer is the possibility that the breaker was not, in fact, made by the company whose name is on the label, that it is a fake.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
off and tripped are two different things. I can't see any way that a functioning breaker would go from the closed to the open position on its own, short of some really bizarre failure or design flaw. For multiple units to do so, seems extremely remote.

the fact that the poster states that he saw it happen suggests one of three possibilities - that he is a troll, that he is mistaken and it is actually tripped, or that there is something really strange going on.

I would point out though that the poster is brand new.

Occam's razor suggests the most likely answer is not the third possibility, although the idea of divine intervention may have some merit. :)
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
All I can offer is the possibility that the breaker was not, in fact, made by the company whose name is on the label, that it is a fake.
I might buy that for a single unit but the OP claims he replaced it multiple times. The chances of getting a fake CB multiple times seems remote, unless the supply house he is using is engaged in some serious fraud.

OP - did you acquire all the replacement breakers from the same supply house?
 
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petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
I am led to believe there is a floating neutral somewhere. I spent the entire day Saturday isolating all grounds/neutrals (aside from main bonding jumper), I removed all feeders/branch and tested/meggered bussing on the panel, I then unplugged all equipment and tested/meggered all branch to the equipment. My tests showed no faults on my wiring at all.
I don't see how a floating neutral would cause a CB to switch from the on to the off position even it was a GFCI.
 
Might a floating neutral explain the 120v branch circuit trips, if those three breakers are on the same phase?

OP, were they? Or were they vertically adjacent, so that a heat problem would unite them?

Perhaps the main breaker's woes are an independent problem. If all three (four?) of those came from the same source, they might all share a defect, or might all be counterfeit.

Any chance that physical shock/vibration is affecting these breakers? Is there a source near the panel of a powerful magnetic field?
 

kwired

Electron manager
Location
NE Nebraska
Might a floating neutral explain the 120v branch circuit trips, if those three breakers are on the same phase?

OP, were they? Or were they vertically adjacent, so that a heat problem would unite them?

Perhaps the main breaker's woes are an independent problem. If all three (four?) of those came from the same source, they might all share a defect, or might all be counterfeit.

Any chance that physical shock/vibration is affecting these breakers? Is there a source near the panel of a powerful magnetic field?
Floating neutral only causes imbalanced voltages across phases with phase to neutral loads. This can and does result in increased current, but often not enough to cause instantaneous trip level currents, and by the time thermal overload trip happens some damage has usually resulted to the load subjected to it. If it makes it through and is operable afterward, it only keeps working on that damage every time it happens, sooner or later something will completely fail if this is what is happening.
 

big john

Senior Member
Location
Portland, ME
In case anyone missed this part.
I remained there for another hour or so, then as I watched it, the 400A main again simply turned off by itself. Absolutely no one else in the room with me.
Thanks, I did miss that.

What was the model of recorder, did it have a fast-capture setting? It's not uncommon for them to only sample every couple of seconds which means an instantaneous fault would easily be missed.

I think you need to re-record the load-side of the 400A main and given that this apparently isn't human-intervention and you claim you're having difficulty with multiple breakers, I think thermography is warranted.
 

brian john

Senior Member
Location
Leesburg, VA
Might a floating neutral explain the 120v branch circuit trips, if those three breakers are on the same phase?
Are you referencing a ungrounded neutral? A ungrounded system would not trip on the first phase to ground fault, after that it would depend on what phase the the second fault as on if a CB would trip or not.

If the OP has one of the replaced CBs in his possession I will test them for free if he sends them to me.
 

iceworm

Curmudgeon still using printed IEEE Color Books
Location
North of the 65 parallel
Occupation
EE (Field - as little design as possible)
... Then the employees told me about 5 minutes after those tripped the 400A went down. Again, it went into the off position.
... I remained there for another hour or so, then as I watched it, the 400A main again simply turned off by itself. Absolutely no one else in the room with me. ....
RTL -
As others have said:
A floating neutral is not going to make a CB turn its self OFF.
An OC trip is not going to turn a CB OFF.
OV is not going to turn the CB OFF
A shunt trip won't either.

Megering is not going to find the issue.

A disturbance analyzer is not going to find it.

SQD confirmed that. The CB is not designed to turn itself OFF - TRIP yes, OFF no.

Just on the off chance you are not trolling us and all the things you said you observed are absolutely true/correct: Then you are missing something. The two I would pick are;
The CB is actually going to the TRIP position as opposed to OFF position.
There is an electric operator installed​

You never did give us the CB cat number. Seriously, has it got an electrical operator?

You have a real Sherlock Homes, locked room murder. Probably time to hire an expert - cause we are not going to get it without the rest of the story.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
I never thought about some kind of operator that might be on it. But that would not account for the branch breakers shutting down unless they also had some kind of operator that is not mentioned in the OP.
 

kwired

Electron manager
Location
NE Nebraska
A typical through the door type of operator will still allow the breaker to trip. If it has mechanical latch that doesn't let you open the door unless the operator is in the off position, then placing the operator in off position will reset the breaker to the off position before you get the door open to see the breaker.

This not so common on panelboards but would be on switchboard or motor control center or some other industrial control cabinets.
 

iceworm

Curmudgeon still using printed IEEE Color Books
Location
North of the 65 parallel
Occupation
EE (Field - as little design as possible)
I never thought about some kind of operator that might be on it. But that would not account for the branch breakers shutting down unless they also had some kind of operator that is not mentioned in the OP.
Nope, it would not. Possibly more than one problem/issue

A typical through the door type of operator will still allow the breaker to trip. If it has mechanical latch that doesn't let you open the door unless the operator is in the off position, then placing the operator in off position will reset the breaker to the off position before you get the door open to see the breaker.

This not so common on panelboards but would be on switchboard or motor control center or some other industrial control cabinets.
Why guess? Wait until we get a cat number and accessory list.
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
Having worked for both Sq. D and Siemens, I can attest to the fact that the breaker CANNOT move from On to Off on its own, doing so would violate NEMA design standards. Even with a shunt trip or under voltage release, the device operates the TRIP bar, so the breaker moves to the Tripped (center) position, not Off. Even the mechanical force of opening a dead short at the maximum interrupt capacity of the breaker is not allowed to over travel the handle mechanism to the full Off position. There must be a distinctly different Tripped position.

It's possible that there was a defective breaker. Siemens had a recall a decade ago on some 400A frame Sentron breakers because of a similar issue, having to do with a small plastic part in the handle that was out of spec and could break off, which could interfere with the proper handle operation, one possible outcome of which was reported to be the lack of a trip position. But 3 defective breakers with the exact same defect that Sq. D is unaware of? Not likely.

POSSIBLY there is a motor operator on this breaker that the OP is unaware of. It might be tied to some sort of energy or power quality monitoring system and when it sees something going wrong, is MOTORING the main breaker open on purpose. Something like a Sq. D Powerlink MVP system. For all we know, this could be completely normal, the OP has never reported back a part number for the breaker.
 

JFletcher

Senior Member
Location
Williamsburg, VA
Hello. I have an extremely unusual situation occurring in a recently wired building and I'm at my wits end with trying to figure this out.
Did you recently wire it, or someone else?

It is a 400A 3phase jawed meter UG service supplying power to a coffee joint.
How big/fancy a coffee joint? Those commercial grade espresso machines draw a LOT of power.

The facility was up and running flawlessly for 2 months, then I started getting calls saying multiple GFI circuits would trip simultaneously.
wag, but the equipment isnt being cleaned correctly.

Please note all the branch 120v circuits were installed with separate neutrals.
How do you know this?

I've since changed that main breaker 3 times as each one did the same thing.
Are these new breakers from a supply house or remfg/used ones?

What are your load readings coming into the main? It's possible that the majority of the load is on one phase.

I remember reading a while ago re: some fancy coffee machines that did not play nice with GFCI. I dont remember the name, but getting a listing of all the equipment might not hurt... certainly would be faster than tearing the building apart and rewiring it.
 

big john

Senior Member
Location
Portland, ME
...POSSIBLY there is a motor operator on this breaker that the OP is unaware of....
You ever heard of one being concealed in the breaker so it wasn't obvious? I would wager no such animal exists.

Call me cynical but I have read a number of cases on threads like these were people have claimed to see dumb MCCBs turning off or tripping in big groups, and I don't recall ever hearing an explanation for any of those events. It's one of those things I chock up to electrician folklore.
 
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