# main trips



## blueheels2 (Apr 22, 2009)

Years a go I was working at NC State in their textiles building. This place is massive (city block big). I was finishing up for the day and I noticed the breaker didnt seat properly in the panel. Rather than take the cover off I put my screw driver on the breaker and gave it a tap to try to get it to seat. It broke and the screwdriver hit the energized terminal on the breaker and shorted out the panel. I looked for 2 hours for the breaker to reset the panel. I found Electrical rooms A and c but couldn’t find B. As all of the students left and it got quiet I was walking down the hall and passed the janitors closet. And surprise I could hear the hum of transformers through the door. Found a janitor and had the door unlocked to Janitors Closet/Electrica Room B. Sorry that’s a long story to tell you I have no idea why your main tripped but I do feel your pain.


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## Quickservice (Apr 23, 2020)

crw16 said:


> I had an incident where a fault in a panel branch circuit, 3 floor commercial apartment bldg, 277v heat circuit. instead of branch breaker tripping out near fault the main breaker in the distribution equip tripped instead. Any input as to why branch brkr didnot trip?


I have seen that a few times. Usually the branch breaker had gone bad, but in one instance the (Up stream) main was way too sensitive. One time I actually encountered (In an apartment complex) a Murray main that was tripping before the Square D branch breaker down stream from it... blew my mind. I jumped the Square D rep about it (Which pi**ed him off), and he claimed that the old Murray's were 100% magnetic which often made them super sensitive.


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## radio208 (Aug 27, 2014)

Had the same problem at school I was at. Fault in lighting circuit in a classroom took out the main breaker feed. Turns out the fault adjuster was set WAY to low in the main service.


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## gpop (May 14, 2018)

For a honest response you would have to tell us the brand and model number of the main breaker. If the breaker is a smart breaker we will also need to know where the dials are set.


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## SWDweller (Dec 9, 2020)

crw16 said:


> I had an incident where a fault in a panel branch circuit, 3 floor commercial apartment bldg, 277v heat circuit. instead of branch breaker tripping out near fault the main breaker in the distribution equip tripped instead. Any input as to why branch brkr didnot trip?


The short answer is no fault study done. Meaning no coordination. Coordination in this sense means the smallest breaker trips. Does not cause a cascade affect. 

Some jobs require a fault/coordination study to be done. This means using the settings created by the PE that is signing the study. I know enough about the math to be dangerous.

I once did a shop building for a school being fed by 3000 amp 480v 3 phase service. One light switch in a class room with 11 4 lamp 277v ballasts would trip the 3000 amp main. Took GE 2 days of reprogramming their ground fault scheme in their breaker. This was decades before the RMS sensing equipment we use today.


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## micromind (Aug 11, 2007)

If the main breaker is 1000 amps or more, it has ground fault sensing. If the fault was phase to ground, almost certainly the main tripped on ground fault.

In my experience, coordination study or not, the ground fault in the main will trip before a 20 amp branch breaker.


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## SteveBayshore (Apr 7, 2013)

We stopped installing 277 volt lighting on the plants we work on years ago because of shorted ballasts tripping the 1000 to 3000 amp ground fault sensors in the mains.


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## Tonedeaf (Nov 26, 2012)

The trip settings on the big breaker are not coordinated with the downstream breakers......I don't know the type of breaker but either the instantaneous trip, ground fault trip curves are faster than the 1 pole 277V breaker.

If the big breaker has settings either dials or some times programable chips you need to adjust the settings.

lots of times the big breakers never get set right at the initial installation. Usually the engineer will put the correct setting the drawings.


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## Quickservice (Apr 23, 2020)

Tonedeaf said:


> The trip settings on the big breaker are not coordinated with the downstream breakers......I don't know the type of breaker but either the instantaneous trip, ground fault trip curves are faster than the 1 pole 277V breaker.
> 
> If the big breaker has settings either dials or some times programable chips you need to adjust the settings.
> 
> *lots of times the big breakers never get set right* at the initial installation. Usually the engineer will put the correct setting the drawings.


Yes, and at times I have wondered if the maintenance people have messed with the settings.


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## micromind (Aug 11, 2007)

Quickservice said:


> Yes, and at times I have wondered if the maintenance people have messed with the settings.


I've seen that more than once.......one time all the settings were turned all the way down in an effort to impress the resident safety nazi. Only trouble was that the long-term trip was adjustable and it was turned down below that actual current..........that's when I got involved.


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## Elec-Tech (Oct 10, 2009)

SteveBayshore said:


> We stopped installing 277 volt lighting on the plants we work on years ago because of shorted ballasts tripping the 1000 to 3000 amp ground fault sensors in the mains.


Easy fix is to fuse the fixtures.


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## SWDweller (Dec 9, 2020)

I disagree about just adding in fuses. Every time I have seen fuses used with breakers It took an smart PE to get the settings on the breakers and fuses correct. Most distribution systems I have work on or near are all breakers. No I have not done much line work in the last decades.


To Steve Bayshore, I submit there was something else wrong with your electrical system if a shorted ballast was tripping the GF on distribution breaker. I do remember an ice cream push cart for a stadium that was tripping the GF on a 1200 amp 480v main. Took several hours to find it. Once found I placed a BO tag and cut the cord flush with the tank. There were lots of screams from the vendor just before the game. the end zone power stayed on for the event. 
BO= bad order for those that may not know the short hand.


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## JRaef (Mar 23, 2009)

Quickservice said:


> Yes, and at times I have wondered if the maintenance people have messed with the settings.


“Breaker tripped on the lighting boss!”
“Is there a dial on it?”
“Yes boss.”
“Well then, crank it up and get back to work…”


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## micromind (Aug 11, 2007)

JRaef said:


> “Breaker tripped on the lighting boss!”
> “Is there a dial on it?”
> “Yes boss.”
> “Well then, crank it up and get back to work…”


This is the standard for IEC motor O/Ls too.........

And sometimes, after the motor burns up it's like 'ok, put it back to where it was so we can blame that dumb electrician'.


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## Scubahigh97 (Aug 18, 2021)

crw16 said:


> I had an incident where a fault in a panel branch circuit, 3 floor commercial apartment bldg, 277v heat circuit. instead of branch breaker tripping out near fault the main breaker in the distribution equip tripped instead. Any input as to why branch brkr didnot trip?


Curve set to low


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## paulengr (Oct 8, 2017)

crw16 said:


> I had an incident where a fault in a panel branch circuit, 3 floor commercial apartment bldg, 277v heat circuit. instead of branch breaker tripping out near fault the main breaker in the distribution equip tripped instead. Any input as to why branch brkr didnot trip?


1. Bad breaker either not tripping or spuriously tripping.
2. Coordination issue…both are working correctly but not working together.

Generally with breakers they can be tested but it’s very expensive for just a couple breakers.

On UL 489 breakers first step is check their series rating (if any). If there is no series rating no guarantee they will coordinate. Google manufacturer and series rating.

Next is check the trip curves (tine current curves). If they do not overlap, that’s good. If they cross, you have a coordination issue at certain fault currents. Again it’s all published data, Google it.

If this is all correct then either the main is tripping early or the branch is late or not tripping at all. There is no way short of testing to prove which one is malfunctioning but I’d replace the branch breaker since it’s the cheaper of the two,


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## Majewski (Jan 8, 2016)

Quickservice said:


> Yes, and at times I have wondered if the maintenance people have messed with the settings.


A maintenance tech messing with it? Oh no that NEVER happens


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## taglicious (Feb 8, 2020)

Found a KO seal in a jbox trippin out new 1200 gfi main. Took 4 of us to find it. Lol i said ok listen for the pop, we'll find it eventually 🤣 it would happen an hour after startup


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## brian john (Mar 11, 2007)

taglicious said:


> Found a KO seal in a jbox trippin out new 1200 gfi main. Took 4 of us to find it. Lol i said ok listen for the pop, we'll find it eventually 🤣 it would happen an hour after startup





taglicious said:


> Found a KO seal in a jbox trippin out new 1200 gfi main. Took 4 of us to find it. Lol i said ok listen for the pop, we'll find it eventually 🤣 it would happen an hour after startup


Thats why they make meggers so you do not find faults by "tripping ANY circuit breaker"


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## taglicious (Feb 8, 2020)

Short of the long. Found the ckt. Isolated the sound. Hopped above tgrid on a lift.


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## Mbit (Feb 28, 2020)

Assuming the dials were ever set correctly.

8 out of ten time when testing breakers I would ask the electricians for the settings and they would look at us cross eyed.

I would just leave them how I found them and not it in my report. There are a ton of breakers out there set to minimums even though a study was done.


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## Spark Master (Jul 3, 2012)

Every breaker has a Fault current rating.... as well as the 20 amps or 15 amps or whatever.


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