600-Amp Breaker Tripped

[Ravenvalor]

Hello,

On Saturday at about 10:00AM a restaurant customer of mine called and reported to me that a 600-amp, 208-volt breaker had tripped. They immediately turned it back on without any problem. It feeds a panel that feeds 7 - AC condensing units, a lighting panel, a dishwasher booster heater and a toaster conveyor. I went to the restaurant and measured the current at the breaker and it was only A-100-amps, B-150-amps, and C-200-amps (per each leg). The breaker is only 11 years old. I checked the AC units with the HVAC tech and we found nothing. I noticed that the trip settings were rather low on this breaker though. Two of the three were set all the way down to minimum. Could these low settings help explain why the breaker tripped?

Thank you,

 

[templdl]

Hello,

On Saturday at about 10:00AM a restaurant customer of mine called and reported to me that a 600-amp, 208-volt breaker had tripped. They immediately turned it back on without any problem. It feeds a panel that feeds 7 - AC condensing units, a lighting panel, a dishwasher booster heater and a toaster conveyor. I went to the restaurant and measured the current at the breaker and it was only A-100-amps, B-150-amps, and C-200-amps (per each leg). The breaker is only 11 years old. I checked the AC units with the HVAC tech and we found nothing. I noticed that the trip settings were rather low on this breaker though. Two of the three were set all the way down to minimum. Could these low settings help explain why the breaker tripped?

Thank you,

Interesting settings. The first thing that I would ask is is the settings were specifically specified be someone for coordination. If not they could be the factory settings and just left there which is not all that unusual.
The first thing that I would do is set that inst. up to 10x. The others two settings are often adjusted for coordination with down stream breakers which they probably are not anyway.
I would put my money on the inst. as the cause of trip though.

 

[Ravenvalor]

Interesting settings. The first thing that I would ask is is the settings were specifically specified be someone for coordination. If not they could be the factory settings and just left there which is not all that unusual.
The first thing that I would do is set that inst. up to 10x. The others two settings are often adjusted for coordination with down stream breakers which they probably are not anyway.
I would put my money on the inst. as the cause of trip though.

This is nice to hear, thanks. The customer was looking at renting a breaker so we could carry this one to a shop to have inspected. He sounded relieved when I told him it may be just a factory setting on the breaker.
Thank you,

 

[big john]

...I would put my money on the inst. as the cause of trip though.

Agreed. There are almost no circumstances I would expect to see an instantaneous of 1.5x, that's just inviting nuisance tripping during a hard compressor start or something similar.

 

[Cow]

I have a hard time believing a restaurant with a 600 amp breaker set to a 900 amp instantaneous trip is going down due to a hard compressor start. This being a restaurant with multiple smaller AC units, rather than one large AC unit. Now one big unit trying to start, I could believe.

I'd be inclined to do a FOP test and a thermal scan of the breaker. Since it reset right away, it doesn't sound like a ground fault, so I don't see any reason to meg anything. Yet.

 

[jbelectric777]

breaker tripped

breaker tripped

wow that's low.

 

[Ravenvalor]

I probably should have interjected this earlier but I did not want to overcomplicate the description.

At the same time the breaker tripped one of the smoke detectors in one of the HVAC units set off the fire alarm system and notified the fire department. It reset itself afterwards.

 

[Ravenvalor]

I probably should have interjected this earlier but I did not want to overcomplicate the description.

At the same time the breaker tripped one of the smoke detectors in one of the HVAC units set off the fire alarm system and notified the fire department. It reset itself afterwards.

Also, this is not a shunt trip breaker.

 

[big john]

I have a hard time believing a restaurant with a 600 amp breaker set to a 900 amp instantaneous trip is going down due to a hard compressor start.

I could see it: If he's running nominal load of ~200A he only needs to make up 700A of inrush to dump that breaker, even a 35HP load might be enough to do that.

That said, I didn't see the bit about a bunch of little condensers, so I agree, not likely to see a large motor load in there.

...At the same time the breaker tripped one of the smoke detectors in one of the HVAC units set off the fire alarm system and notified the fire department. It reset itself afterwards.

The plot thickens. That HVAC unit still running?

 

[Ravenvalor]

I could see it: If he's running nominal load of ~200A he only needs to make up 700A of inrush to dump that breaker, even a 35HP load might be enough to do that.

That said, I didn't see the bit about a bunch of little condensers, so I agree, not likely to see a large motor load in there. The plot thickens. That HVAC unit still running?

All of the HVAC units are on the same zone so we could not identify which one of the seven set off the alarm. The one that tripped did reset itself so we could not physically find it either.

 

[beefeater]

My bet is that something faulted and then cleared itself. Good chance that it was a resistive heating element in the booster, toaster or one of the HVAC systems. Was it possibly the first cool morning of the season? Chances are one of those is running but not performing at full capacity.

 

[templdl]

All of the HVAC units are on the same zone so we could not identify which one of the seven set off the alarm. The one that tripped did reset itself so we could not physically find it either.

See once it's an electronic trip breaker how old is it? If it is old enough it may be asnd older technology peak sensing breaker. The newer technology used microprocessor technology which incorporates RMS sensing technology. The older technology is more prone to nuisance trips which are caused by voltage spikes.
It is interesting to note the various and amusing guesses that have been suggested here as there is no way of telling if trip was thermal or magnetic. In addition in most cases you get there some time after the even and if the breaker doesn't have an indicator showing how it triped there in nothing but to guess at its cause.
As I pointed out in my first post I opted for theminimum setting of the instantaneous trip which most likely was as supplied from the factory that way. There is NO REASON for it to have Ben left in that position. That incident regarding the HVAC may have lead to a trip.
But one thing that you do learn is there is no way that the crime can be recreated in most cases.
I had a main 400at electronic trip breaker of the older peak sensing type at a sewrage lift station that was habitually tripping at 5am. It was getting a bit old with the city that they were called out frequently to reset and close the breaker. 5am in the morning probably cause by the power company switching a PFC bank to correct power factor the resulting voltage spike caused a current spick tripping there breaker instantaneously. After a meeting at the Waste water treatment plant office sitting around a very big oval table with 10 people attending with their attention directed toward me I told them that I had a solution which I would work with my customer with. Knowing that there really wasn't anything wrong with that breaker I asked my warranty manager for as favor asking him for a 400a breaker of the older type with a physically thermal magnetic trip and gave it to my customer to replace. Problem solved.
I could have gone through a bunch of crap putting a recorder of the system but making a simply observation was more practical.

 

[mayanees]

Inst

Inst

I concur that the Instantaneous setting at 1.5X is the likely culprit, and that it should be increased. But be aware of arc flash considerations. That inst increase will likely cause a significant increase in the arc flash incident energy level, and if it's currently labeled, will negate the reported results.

 

[steve66]

So its been this way for 11 years, and hasn't tripped before.

I agree the instantaneous could be raised a little, but setting it to 3 would be 1800 amps. That should be enough to prevent any tripping unless there is a real problem.

But since this has never tripped before, my guess is there is something else going on, and my money is on a bad condensing unit or RTU.

I know of one CU that was on a 70A breaker, but it tripped an 800 A main several times over the span of about a week, and the 70A never tripped. The CU also had internal overloads that also tripped (and were reset) several times. But this place had a large maintenance dept, and the two never seemed to trip at the same time. One guy would respond to the tripped 800A, and another guy was resetting the CU. It took a while for them to put 2 and 2 together.

 

[zog]

This is nice to hear, thanks. The customer was looking at renting a breaker so we could carry this one to a shop to have inspected. He sounded relieved when I told him it may be just a factory setting on the breaker.
Thank you,

Besides the trip unit there isn't much to inspect, that breaker can be tested in place via secondary injection to determine if it is a problem with the trip unit. Quick easy job if you have the right test set.

 

[jim dungar]

See once it's an electronic trip breaker how old is it? If it is old enough it may be asnd older technology peak sensing breaker. The newer technology used microprocessor technology which incorporates RMS sensing technology. The older technology is more prone to nuisance trips which are caused by voltage spikes.

The OP breaker said the breaker was only 11 years old. I know of no major manufacturer of breakers that did not stop using Peak Sensing technology some 25-30 years ago.

It also doesn't make much difference whether the breaker tripped on long time (roughly 130%) or instantaneous (150% per the dial).
The simple fact is; no one ever performed any type of coordination study for this main breaker and its feeders.

This main breaker is a 'backfed' I-Line breaker, therefore it does not offer any arc flash protection to the panel it is installed in.

Now the correct question is; which branch/feeder should have tripped, and why?

 

[Jraef]

...Now the correct question is; which branch/feeder should have tripped, and why?

Ding ding ding! Winner!

Sounds to me as though a coordination study is in order. You want the protective device CLOSEST to the fault to be the first thing that trips. Had that been the case, you would KNOW which piece of equipment caused it.

I suggest they contact a NETA certified testing agency with a PE on staff (or separately) in their area to not only test that breaker in situ, but to look at the system as a whole with regard to trip coordination, called a "Coordination Study". Any facility should have one, and ESPECIALLY if a nuisance trip of a main breaker will cost them money in down time and lost revenue. They likely have ALREADY lost the money they would have spent on a Coordination Study, so tell them to do it now before it happens AGAIN. If you guess and set something for them, and it DOES trip again and costs them money, they are going to blame YOU.

 

[jim dungar]

.... test that breaker in situ...

This is pretty much a waste of money. They first need to coordinate the breakers. The coordination can likely be done using the naked eye and published trip curves.
This system has been in place for some 11 years, it is probably not an incident waiting to happen.

 

[Jraef]

This is pretty much a waste of money. They first need to coordinate the breakers. The coordination can likely be done using the naked eye and published trip curves.
This system has been in place for some 11 years, it is probably not an incident waiting to happen.

I only mentioned the testing in situ because he was speaking of buying a new 600A breaker and sending the old one out to be tested. It would be far cheaper to have someone come there and test it, because it's most likely fine.

If he doesn't know what a coordination study is, it's unlikely he is capable of doing it on his own...

 

[Ravenvalor]

The OP breaker said the breaker was only 11 years old. I know of no major manufacturer of breakers that did not stop using Peak Sensing technology some 25-30 years ago.

It also doesn't make much difference whether the breaker tripped on long time (roughly 130%) or instantaneous (150% per the dial).
The simple fact is; no one ever performed any type of coordination study for this main breaker and its feeders.

This main breaker is a 'backfed' I-Line breaker, therefore it does not offer any arc flash protection to the panel it is installed in.

Now the correct question is; which branch/feeder should have tripped, and why?

Just to reclarify, The breaker is not a main breaker. Someone had labeled that breaker by mistake. It front feeds from bus. Conductors leave the breaker and travel about 3' to another panel.

Thank you for the help.