# Adjustable trip breakers



## NolaTigaBait (Oct 19, 2008)

Can someone explain the purpose of them?...When would you need to adjust them?


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## jwjrw (Jan 14, 2010)

I believe it is to aid in coordination of breakers.


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## brian john (Mar 11, 2007)

NolaTigaBait said:


> Can someone explain the purpose of them?...When would you need to adjust them?


Coordination between upstream and downstream circuit breakers, better protection, allow loads to come on line.

Assume a 1000 amp CB feeds only lighting loads the INSTANTANEOUS portion might be set at 4X or 4000 amps, the same CB feeding multiple transformers may be set at 12X or 12, 000 amps.

In addition a 1000 amp CB with a Long Time Setting of .4-1.0 can be a 400, 500, 600, 700, 800, 900 or 1000 amp CB (settings vary from manufacture to manufacture).

I did not fully read these articles.

http://smtp.miamibreaker.com/pdf/AMCCBGB.pdf

http://www.articlesnatch.com/Article/What-You-Need-To-Know-About-Circuit-Breakers-/928301


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## NolaTigaBait (Oct 19, 2008)

The reason I ask is that I installed a 150 siemens bqd breaker...It has a low to high adjustment that goes from 800 to 1500...


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## NolaTigaBait (Oct 19, 2008)

I read both, still not getting it:jester:


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## brian john (Mar 11, 2007)

NolaTigaBait said:


> The reason I ask is that I installed a 150 siemens bqd breaker...It has a low to high adjustment that goes from 800 to 1500...


This is an adjustable INSTANTANEOUS so the trip ranges are from 800 amps to 1500 amps or 5.33 times 150 amps to 10 times 150 amps. Typically an engineer should give you the settings for this CB.

This adjustment lets you determine the trip setting to over come instantaneous inrush typical of transformers and motors. At the low setting the CB might trip every time you tried to turn it on. So the adjustment allows you to account for this current. Yet there are times you might need the low setting such having this CB trip in lieu of the next upstream CB tripping. 

This depends on the curves as submitted by the manufactures. See Erics post about teaching OCP's.


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## Zog (Apr 15, 2009)

NolaTigaBait said:


> The reason I ask is that I installed a 150 siemens bqd breaker...It has a low to high adjustment that goes from 800 to 1500...


150A is your overload protection, the breaker will trip at 150A after a couple minutes, and faster at >150A. You find the exact times from a trip curve. 

Your 800-1500A setting is for your fault protection, it will trip very quickly at the set current. This adjustment allows you to protect different types of loads, for example a motor will have a high starting current and you do not want it to trip the breaker when it starts, so it would be set above the starting current. Linear loads generally would have lower settings. The proper setting is determined by a coordination study.


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## NolaTigaBait (Oct 19, 2008)

Thanks guys. I understand a little better now..This breaker is going to feed a group of 6 welders.


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## sparky.jp (May 1, 2009)

Well, an adjustable-trip circuit breaker allows you to modify one or more of the time-current characteristics of the device. The graphical way that the trip characteristics is shown is known as a time-current-characteristics (TCC) curve, which has amps on the horizontal axis and time on the vertical axis. In general, most devices have an inverse relationship between time and current, ie the more current flowing though the device, the shorter the time to trip.

With fixed-curve devices such as most smaller molded-case circuit breakers (MCCBs), you cannot adjust the time-current curve. In order to have coordination between overcurrent devices that are placed in series, it is often advantageous to be able to modify the parameters of the time-current curve on any given device in the string. Coordination refers to the desire to have only the overcurrent device closest to the fault trip, while the upstream devices stay on in order to minimize the electrical outage to the facility or system.

When you plot multiple time-current curves on the same chart, you will want the downstream trip device's curve to be the closest to the origin, and then have the TCCs "nest" as you go from the lower left to the upper right on the chart. That is the ideal situation and seldom does it work out that way in the real world. Coorination becomes more important at critical facilities (communication centers, oil refineries, large industrial sites, and so on) where the potential economic impact of a large system outage can be devastating not to mention life-threatening.

There are other reasons one might want to modify the time-current characteristics of a trip unit as well, such as to allow a motor to have a large inrush current during starting without nuisance tripping of the device.

In addition, the ability to be able to adjust the breaker trip characteristics gives the manufacturers much more flexibility in that they can offer just a few breaker frame sizes which will work for a very wide range of operating and interrupting currents. 

Typically the breaker settings are chosen by the engineer or designer to meet the needs of the design, based upon a fault-current and coordination study, and of course the settings must be done to meet the NEC requirements as well for proper conductor protection. 

Does this help any? There is a lifetime's worth of reading out on the internet regarding this topic, I would recommend the white (technical) papers at the Schneider Electric (Square-D) website for starters.

EDIT: wow, lots of others answered many items while I was entering this in a far simpler way, sorry for the long post.


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## brian john (Mar 11, 2007)

sparky.jp said:


> Typically the breaker settings are chosen by the engineer or designer to meet the needs of the design, based upon a fault-current and coordination study, and of course the settings must be done to meet the NEC requirements as well for proper conductor protection.


Unfortunately many times the engineers shuck their responsibility or the electricians have no clue to do with a coordination study and we find the settings all at minimum. And in worse case this happens on Sunday morning at 2:00 AM and there are multi-level CBs opened.


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## Zog (Apr 15, 2009)

brian john said:


> Unfortunately many times the engineers shuck their responsibility or the electricians have no clue to do with a coordination study and we find the settings all at minimum.


Then some yahoo "cranks them up" to the max settings thinking he resolved a problem


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## Zog (Apr 15, 2009)

sparky.jp said:


> EDIT: wow, lots of others answered many items while I was entering this in a far simpler way, sorry for the long post.


I tried to keep it basic. However Nola, Ihave tons of material on the topic (From my teaching days) if you have any more questions.


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## NolaTigaBait (Oct 19, 2008)

Zog said:


> I tried to keep it basic. However Nola, Ihave tons of material on the topic (From my teaching days) if you have any more questions.


Yeah, plenty of questions...you may be here all night though. The breaker in question feeds a group of welders and I doubt its the end of the world if they trip...I just would like to know the reason behind the settings.


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## nrp3 (Jan 24, 2009)

Sounds like adding a panel in say a hospital or maybe a manufacturing plant could be tricky if you don't know what you are doing. Thats to say not the physical aspect of it but gettting those breaker settings right. Adding a new load might affect the settings elsewhere?


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## Zog (Apr 15, 2009)

NolaTigaBait said:


> Yeah, plenty of questions...you may be here all night though. The breaker in question feeds a group of welders and I doubt its the end of the world if they trip...I just would like to know the reason behind the settings.


Then set them at the minimum setting as BJ mentioned. You can ask for coordination settings and when they stare at you like you have two heads mumble "Then I will set them to the default settings". 

Have you looked at a trip curve yet? Any questions about a trip curve? Look at the times and currents and see how they are logrithmic? That is the key to reading them right, knowing how to read a logrithmic scale.


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## Zog (Apr 15, 2009)

nrp3 said:


> Sounds like adding a panel in say a hospital or maybe a manufacturing plant could be tricky if you don't know what you are doing. Thats to say not the physical aspect of it but gettting those breaker settings right. Adding a new load might affect the settings elsewhere?


Always ask for the settings to be provided. Get blank stare, mumble as mentioned above. :001_huh:


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## brian john (Mar 11, 2007)

nrp3 said:


> Sounds like adding a panel in say a hospital or maybe a manufacturing plant could be tricky if you don't know what you are doing. Thats to say not the physical aspect of it but gettting those breaker settings right. Adding a new load might affect the settings elsewhere?


And that is were we come in (HOPEFULLY) we work with the engineers to obtain a coordination study and then set the CB and test it.


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## nrp3 (Jan 24, 2009)

How do you test something like that without potential damage or disrupting operations? Off hours?


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## NolaTigaBait (Oct 19, 2008)

Zog said:


> Then set them at the minimum setting as BJ mentioned. You can ask for coordination settings and when they stare at you like you have two heads mumble "Then I will set them to the default settings".
> 
> Have you looked at a trip curve yet? Any questions about a trip curve? Look at the times and currents and see how they are logrithmic? That is the key to reading them right, knowing how to read a logrithmic scale.


I haven't looked at a trip curve...I've seen one, but never actually studied it:jester:


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## sparky.jp (May 1, 2009)

nrp3 said:


> How do you test something like that without potential damage or disrupting operations? Off hours?


You utilize the services of a certified testing company which will come in with a circuit breaker test machine that will run (low-voltage but) high current through the breaker to verify that it trips when it is supposed to.

Typically done before a facility is started up - on an operational facility, yes, it is more difficult, off-hours during the midnight shift is not uncommon.


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## Zog (Apr 15, 2009)

NolaTigaBait said:


> I haven't looked at a trip curve...I've seen one, but never actually studied it:jester:


Well it is the first thing to learn to answer your question, anything I try to explain will reuire understanding of a trip curves, other guys provided links in earlier posts.


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## brian john (Mar 11, 2007)

sparky.jp said:


> Y, off-hours during the midnight shift is not uncommon.


Lots and Lots of Mid-Night Shifts.

Testing circuit breakers is easy, getting the test set to the job and connecting the CBs is 75% of the job.

That's why testing a single CB is so expensive, we try to talk the customer into letting us bring the CBs to our shop for a one or two CB job.


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## Zog (Apr 15, 2009)

brian john said:


> Lots and Lots of Mid-Night Shifts


Don't forget weekends and holidays. I had my 1st Thanksgixing dinner with my family in 10 years the year I left the NETA testing world.


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## brian john (Mar 11, 2007)

Zog said:


> Don't forget weekends and holidays. I had my 1st Thanksgixing dinner with my family in 10 years the year I left the NETA testing world.


I CHEAT, after 25 years of working every possible holiday I know tell customers that "Oh sorry we already have a job that day, maybe another day?" About 90% pick another day the others I recommend a friends firm.

Memorial Day, Labor Day, Thanksgiving, Christmas and News Year, we still (I) run emergency calls on those days.


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## NolaTigaBait (Oct 19, 2008)

Zog said:


> Well it is the first thing to learn to answer your question, anything I try to explain will reuire understanding of a trip curves, other guys provided links in earlier posts.


Is it a standard chart?..or does it change?


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## Zog (Apr 15, 2009)

NolaTigaBait said:


> Is it a standard chart?..or does it change?


Specific to every different trip unit, breaker, or fuse. For adustable breakers or trip units the curves shift when you change a setting. I can't explain it if you won't bother looking at some. Little effort on your part?


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## NolaTigaBait (Oct 19, 2008)

Zog said:


> Specific to every different trip unit, breaker, or fuse. For adustable breakers or trip units the curves shift when you change a setting. I can't explain it if you won't bother looking at some. Little effort on your part?


:laughing:..I'm not trying to be lazy...just making sure that it isn't a standard chart.


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## NolaTigaBait (Oct 19, 2008)

page 3 ...I believe that is the breaker in questions\:

http://www.sea.siemens.com/us/SiteC.../110607/110607_18/VL-TCC-DG_806992_525_TM.pdf


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## frenchelectrican (Mar 15, 2007)

NolaTigaBait said:


> page 3 ...I believe that is the breaker in questions\:
> 
> http://www.sea.siemens.com/us/SiteC.../110607/110607_18/VL-TCC-DG_806992_525_TM.pdf


 
Yep that one way it will show the ajustable range for that class of breaker.

And I don't know if you are aware or not but some of us are aware there are few diffrent class of trip curve breaker classes.

Something it is common in European side which we have 4 classes of breaker tripping curves they run from class A which it a super fast tripping on very light bolt fault circuit { common used with electronic or computer loads and some SCR drives } Class B is most common one we use in France and it basically the same as you have on your chart that is a run of mill with med surge load capaity and the trip curves are change a bit.
Class C is longer delay and higher insatist trip charasic that is common used with transfomer and motours load but the last one is class D some case they don't trip out very fast that used on welder or hard to start motour loads and very high inrush transfomer loads. { the class D trip fuse / breakers you have to becarefull with their o/l and fault curves }

So that one quick example you will see it.

And Oui., we do have adjustable breakers in Europe as well they are same as Americian counterparts.

Merci.
Marc


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## Zog (Apr 15, 2009)

NolaTigaBait said:


> page 3 ...I believe that is the breaker in questions\:
> 
> http://www.sea.siemens.com/us/SiteC.../110607/110607_18/VL-TCC-DG_806992_525_TM.pdf


So the curved part at the top is your Overload (Thermal/Long time) trip curve, it is an I2t function. At 1.0x your continous current rating (In) ot will trip around 10,000 seconds. At around 14x In it will trip around 10 seconds. To find a trip time you follow the current down until it crosses the line then go across to find your time. When we test these we test at 3xIn, so for this curve we would apply 3xIn and it should trip in 21-57 seconds (The grey area is the tollerance band). 

For the INST (Magnetic) portion of the curve, on the bottom half you see there is no "curve", it is linear because there is no intentional delay. There is a small curve at the bottom which is because this is magnetic and not an electronic trip unit that responds faster. The blue lines show the range of adjustment. To test this function we apply the test current in pulses, starting at -20% of the setting and see where it trips, looking for a current her, not time. 

This is about as simple as a curve gets, adjustable pickups and delays on LT, ST, and GF can make things more complex. But I hope you get the idea.

Now if you took that curve, and draw your load characteristics on that paper, steady state and starting currents versus time, you can see how adjusting them based on your loads can be benificial.


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## NolaTigaBait (Oct 19, 2008)

I'm starting to understand. Thanks, Zog and others. If I wanted to learn more, is there any books that I can buy that will help me..?


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## NolaTigaBait (Oct 19, 2008)

When you say 1x the continuous current rating...you mean if it is a 150 amp breaker, then 1x that?....What does the 800(low) mean on the trip dial?


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## Zog (Apr 15, 2009)

NolaTigaBait said:


> When you say 1x the continuous current rating...you mean if it is a 150 amp breaker, then 1x that?....


In this case yes, In is just the frame size of the breaker. But when you have CT's and/or rating plugs involved that can change. Or when you have adjustable Long Time trips, it will also change. If you have a 1600A breaker with 800A Ct's and LTPU set to 0.8 In=800x0.8=640A. 



NolaTigaBait said:


> What does the 800(low) mean on the trip dial?


 That is your INST trip, in this case your magnetic pickup. Again, when you add CT's and/or rating plugs that would be listed as a multiplier on the trip unit and you need to calulate what current it relates to.


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## Zog (Apr 15, 2009)

NolaTigaBait said:


> I'm starting to understand. Thanks, Zog and others. If I wanted to learn more, is there any books that I can buy that will help me..?


There are plenty, depends on what you want to learn, in the testing world this is our bible
http://search.barnesandnoble.com/El...ce-and-Testing/Paul-Gill/e/9780824799076/#TOC


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## NolaTigaBait (Oct 19, 2008)

Zog said:


> In this case yes, In is just the frame size of the breaker. But when you have CT's and/or rating plugs involved that can change. Or when you have adjustable Long Time trips, it will also change. If you have a 1600A breaker with 800A Ct's and LTPU set to 0.8 In=800x0.8=640A.
> 
> That is your INST trip, in this case your magnetic pickup. Again, when you add CT's and/or rating plugs that would be listed as a multiplier on the trip unit and you need to calulate what current it relates to.


I went back and read some of your posts from yesterday(where you said this already):jester:....It makes more sense now.


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