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Discussion Starter #1
Does anyone have any experience with setting an adjustable trip circuit breaker? I’m having problems with one of the branch circuits in the panel in the picture but it’s tripping an upstream breaker that’s taking the lights out in half the building.

I’m sure there’s a way to adjust the sensitivity so this MB will trip before it gets upstream but I’m not sure what each dial in the picture means. When I first looked I saw all the dials set to 10 so I just figured I should set them to 5 but I’m sure it’s more involved than that.

Thanks

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One point of order, do not make changes under a load. Open the breaker then make your adjustments. This will be the time your project should have a coordination study done.
You will need to get out your current measuring tool. Once you measure the load you can adjust the breaker. The dials are current per phase. Some of the Eaton product line the dials are long,short , instantaneous and ground.
 

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One point of order, do not make changes under a load. Open the breaker then make your adjustments. This will be the time your project should have a coordination study done.
You will need to get out your current measuring tool. Once you measure the load you can adjust the breaker. The dials are current per phase. Some of the Eaton product line the dials are long,short , instantaneous and ground.
Learned that after adjusting about 40 breakers between 800-4000amps on a job with no issues until the last one tripped on me. It was an old 1600 amp ITE for a chiller that was running at the time. As soon as I touched the short time setting I **** my pants. Loud and the concrete basement floor shook as it tripped.


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Chief Flunky
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Here are the curves:


As you can see it’s a 3 pole breaker. I didn’t look to see if the long term trip can be adjusted with a rating plug but essentially the long term is fixed. The “instantaneous” is fixed. All you can adjust is the short time trip. So basically useless. All three dials do exactly the same thing just on different phases.

The way that you have to coordinate with upstream breakers is three fold. First you need to know the available short circuit current. We just need to know the maximum because then you know you don’t need to coordinate above that current. If you don’t know we go to step 2. In this step if the short circuit current is in the instantaneous range of more than one device then you need to know the series rating. You find this by looking up both devices in tables provided by the manufacturers. So if you have an Eaton breaker and say a GR breaker then what? You are out of luck. Instantaneous tripping must be tested, not calculated. There are too many unknown variables. If you are not in that region you are in luck. Plot each device on the same time-current chart using either engineering software costing thousands or hand sketch them. As long as the curves “stack” (no crossing) at every point below the maximum short circuit current, it coordinates.

With the engineering software (SKM, ETap, etc.) in the hands of someone trained to do it you can do these in minutes as long as the devices are in the libraries (with typically thousands of devices). You can also use “Coordinaide” from S&C for FREE as long as your devices are in their database, mostly medium voltage only but I’ve done some non-medium voltage with it too.

Not trying to be intimidating here but the fact is that there is no practical way short of working strictly from series ratings tables or training on power system studies to do coordination studies. It’s typically done by engineers that supply you with the exact settings that work.
 

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Does anyone have any experience with setting an adjustable trip circuit breaker? I’m having problems with one of the branch circuits in the panel in the picture but it’s tripping an upstream breaker that’s taking the lights out in half the building.

I’m sure there’s a way to adjust the sensitivity so this MB will trip before it gets upstream but I’m not sure what each dial in the picture means. When I first looked I saw all the dials set to 10 so I just figured I should set them to 5 but I’m sure it’s more involved than that.

Thanks
If you have a light circuit that's tripping a breaker and throwing the main then adjusting the dials will not make any difference as that is a instantaneous trip.

Speed the breaker trips can tell us a lot about what is going on, Also which breakers trip.

p.s... breakers are only rated to open once instantaneous. Keep throwing it in with out finding/fixing the problem and it can get nasty and cost a small fortune to replace the magic smoke or the real smoke where ever that short is located. instantaneous is probably over 1000 amps.
 

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I had a job where closing a light switch with 12 -277v light fixtures would trip the 3000 amp main.
Only switch in the whole building that would do it. Took GE 3 days with 2 guys to fix the problem.
To long ago to remember what the fix was.

Coordination is a wonderful thing. I used to get tasked to go collect the informaiton for some of PE's in the Chess offices. So that they could do a study. At least you could stay clean for a few days collecting data.
 

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Discussion Starter #8
Thanks guys for the responses, this whole topic is a little over my head I guess. When I saw the three dials I figured I could tune the breaker so it would trip before the ones upstream, I didn’t realize that each dial was specifically for each phase. The panel is for outdoor lighting only and actually has two issues. Circuit #21 is for some ground floodlights that tripped the 200 amp breaker on the main switchgear, it made sense to me because that is the only breaker in that had GFCI protection and I could measure continuity from the hot at the floodlight to the dirt. So I isolated that circuit for future repair and two days later the 200 amp main on the distribution panel between the switchgear and outdoor lighting panel tripped. I couldn’t find anything with the meter but after a few resets it turns out that circuit 2 and 4 are the problem. They go to some pole lights in an area of the parking lot, I’m guessing they are shorting to each other after they heat up and since it’s not actually a ground fault it trips at the distribution panel main. It’s kinda frustrating though because the fault is getting through the main breaker in this panel and the 125amp feeder breaker in the dist. panel.

My bosses decided that after I correct the current problems, I’m going to re-feed the outdoor lighting panel directly from the a spare 100 amp breaker on the switchgear and bypass the lighting distribution panel. Every time the fault happened, it was late in the evening, mostly everyone went home and the CEO was in high level meetings in the board room when all of the lights went out. Twice in three days so my bosses didn’t look so good last week, amazing how fast that overtime budget opened up for me.
 

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Just when you get comfortable in the trade something rears its head and there is an whole another level to learn. Ain't it wonderful.!
 

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Fuses are your friends when it comes to outside lights. Buy a bunch of inline fuses with the rubber covers. Better to pop a fuse and take out one light then to pop the gfci and take them all out.
 

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Discussion Starter #12
Fuses are your friends when it comes to outside lights. Buy a bunch of inline fuses with the rubber covers. Better to pop a fuse and take out one light then to pop the gfci and take them all out.
That’s a good idea.
 

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Chief Flunky
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If you have a light circuit that's tripping a breaker and throwing the main then adjusting the dials will not make any difference as that is a instantaneous trip.

Speed the breaker trips can tell us a lot about what is going on, Also which breakers trip.

p.s... breakers are only rated to open once instantaneous. Keep throwing it in with out finding/fixing the problem and it can get nasty and cost a small fortune to replace the magic smoke or the real smoke where ever that short is located. instantaneous is probably over 1000 amps.
It’s 225 A times the dial so 1125-2250 A.
 

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Does anyone have any experience with setting an adjustable trip circuit breaker? I’m having problems with one of the branch circuits in the panel in the picture but it’s tripping an upstream breaker that’s taking the lights out in half the building.

I’m sure there’s a way to adjust the sensitivity so this MB will trip before it gets upstream but I’m not sure what each dial in the picture means. When I first looked I saw all the dials set to 10 so I just figured I should set them to 5 but I’m sure it’s more involved than that.

Thanks

View attachment 155101
View attachment 155102
Joe,
The solution lies in the adjustments of the upstream breakers. And the issue is that you really need all of the upstream breakers, all the way to the Utility source. If you can provide pics of the upstream breakers as far up as you can get I'll send you the settings to optimize coordination. It should start with a one-line diagram that goes back to the service-entrance in order to optimize the settings. It should also include a closer view of the 120 Volt single-pole breaker that you said started the fault in order to include it in a TCC. Your adjustment of the magnetic (INST) pickup from 10X to 5X needs to be gauged against the upstream breaker's instantaneous response, which is probably a low instantaneous pickup level. It's a 5-10 minute task, and I'd be happy to plot it out if you're interested.
John
 

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Discussion Starter #16
Joe,
The solution lies in the adjustments of the upstream breakers. And the issue is that you really need all of the upstream breakers, all the way to the Utility source. If you can provide pics of the upstream breakers as far up as you can get I'll send you the settings to optimize coordination. It should start with a one-line diagram that goes back to the service-entrance in order to optimize the settings. It should also include a closer view of the 120 Volt single-pole breaker that you said started the fault in order to include it in a TCC. Your adjustment of the magnetic (INST) pickup from 10X to 5X needs to be gauged against the upstream breaker's instantaneous response, which is probably a low instantaneous pickup level. It's a 5-10 minute task, and I'd be happy to plot it out if you're interested.
John
Thanks John! I appreciate the offer but I don’t think they’re going to allow me to adjust the upstream breakers. I found the compromised feed underground so now they want me to focus on correcting that and then work on refeeding this whole panel from another upstream breaker that won’t take out all of the interior lights if it trips. If I can get a chance to remove the cover of the panel upstream I’ll grab a picture of it though because I’d be curious for my own knowledge on how it should be set.

Thanks again!
 
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