I installed 175A new breaker and the next day I had to uninstall it and install new 175A breaker and when I asked why, the PM says because the first one is serie breaker. Is this correct?what serie breaker means? Can someone clarify this concep and pros and cons to use serie breaker?
Series breakers?
- Thread starter marcosgue
- Start date
Series ratings are one way to address available fault current. Series ratings requires specific breakers. There are many links the help explain series ratings. I would suggest "Eaton series rating guide"
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Thank you @augie47 but if still the series breaker can be able to support the load and protect the cable, in this case what do you consider the reason to change the breaker?something in relation with the coordination studies? This breaker 175A is feeding the chiller equipment with MCA=164A, 480V, 3Ph.
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
I believe that if there are not two breakers in series (i.e., the 175 amp and one other between the power panel and the chiller), then the 175 amp breaker having a series rating is irrelevant. It would have been acceptable.
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
A breaker has many ratings: its trip current, its maximum voltage, and its maximum fault current interrupting capacity, among others.
Imagine that you'd installed a 175A 240V breaker. Correct trip rating but the voltage rating is too low for the job. The breaker would likely fail just when it was most needed: as it was trying to trip.
All electrical systems have a maximum available short circuit value, essentially what the transformer can push through the wires into a perfect dead short. The breaker(s) must be able to withstand and open if this maximum possible short circuit is flowing. If the breaker can't handle the available short circuit current, it might fail just when it was most needed.
A fully rated breaker is one that can open against the maximum available short circuit current on its own.
A series rated breaker is _not_ rated to withstand the maximum available short circuit current on its own, but can be used in combination with an upstream breaker or fuse to function with high available short circuit current. The combination of two OCPDs in series is able to open against the fault current.
Imagine that you'd installed a 175A 240V breaker. Correct trip rating but the voltage rating is too low for the job. The breaker would likely fail just when it was most needed: as it was trying to trip.
All electrical systems have a maximum available short circuit value, essentially what the transformer can push through the wires into a perfect dead short. The breaker(s) must be able to withstand and open if this maximum possible short circuit is flowing. If the breaker can't handle the available short circuit current, it might fail just when it was most needed.
A fully rated breaker is one that can open against the maximum available short circuit current on its own.
A series rated breaker is _not_ rated to withstand the maximum available short circuit current on its own, but can be used in combination with an upstream breaker or fuse to function with high available short circuit current. The combination of two OCPDs in series is able to open against the fault current.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Yes.
Many coordination studies also have a short circuit component to look at fault currents to see if the installed equipment has adequate AIC and SCCR ratings.
As Winnie said, the replacement breaker was likely due to it providing a series-rating with down stream equipment.
This type of replacement happens often as the studies are not completed until the equipment has been installed. It is usually cheaper to go back and fix a few items rather than delay the project.
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Strathead
Senior Member
- Location
- Ocala, Florida, USA
- Occupation
- Electrician/Estimator/Project Manager/Superintendent
First, in general, series rating or fully rated (the two options) are generally applies to entire distribution systems when first installed. As Augie said, you would need to do some of your own research and understand the concepts of series and full rating before any of us go to deep here, because it is too complex to explain in a few paragraphs. A couple things that any qualified electrician should know (and MANY don't) when doing service and repair work are: Look in a panel before installing a breaker. Makes sure any new breaker you put in has a AIC rating that is equal to are greater than the lowest AIC breaker in the panel. If you are installing a new breaker downstream from an existing panel it needs to be the same brand as the upstream panel and with an equal or higher AIC rating. If it is a different brand, you generally NEED to have a study done to determine short circuit ratings.
mayanees
Senior Member
- Location
- Westminster, MD
- Occupation
- Electrical Engineer and Master Electrician
The breaker is likely in a fault current environment that exceeds the ratings listed on the breaker. I highlighted the 480V, 25kA rating. In order to series-rate that breaker there is a fuse or breaker that is in series with that breaker that gives it a higher rating than 25kA.
There will be a series-rating chart that lists that breaker with some other device.
There will be a series-rating chart that lists that breaker with some other device.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Can you post a photo of the replacement circuit breaker?
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
You can get some clues from the breaker itself, but need more information to determine if a series rating is being used. Do you have a picture of the new breaker you put in?
If you look at the upper left of your picture, you will see a table that says 'Interrupting Rating'. This tells you the maximum short circuit current that the breaker is capable of interrupting. If you know the available short circuit current at the panel where the breaker was installed, you compare the interrupting rating to that number. You can't figure out the available short circuit current from the breaker itself; it is a characteristic of the electrical system installed. You compare the two numbers. If the available short circuit current is less than the interrupting rating, then the breaker is 'fully rated' for the application.
Now let's say that the available short circuit current is greater than the interrupting rating: then you need to investigate further. You need to check the upstream breaker or fuse, and look at the data sheet for the breaker. If the datasheet says that the breaker you have plus the upstream breaker you have has been tested for your available short circuit current, even though it is greater than the interrupting rating, then you have a 'series rating' situation. Note that the breaker is not a 'series rating', rather all breakers have interrupting ratings, and some of those interrupting ratings are 'series ratings'
Finally if the available short circuit current is greater than the interrupting rating and greater than what the datasheet allows, you have a mis-applied breaker that is not suitable for the application.
If you look at the upper left of your picture, you will see a table that says 'Interrupting Rating'. This tells you the maximum short circuit current that the breaker is capable of interrupting. If you know the available short circuit current at the panel where the breaker was installed, you compare the interrupting rating to that number. You can't figure out the available short circuit current from the breaker itself; it is a characteristic of the electrical system installed. You compare the two numbers. If the available short circuit current is less than the interrupting rating, then the breaker is 'fully rated' for the application.
Now let's say that the available short circuit current is greater than the interrupting rating: then you need to investigate further. You need to check the upstream breaker or fuse, and look at the data sheet for the breaker. If the datasheet says that the breaker you have plus the upstream breaker you have has been tested for your available short circuit current, even though it is greater than the interrupting rating, then you have a 'series rating' situation. Note that the breaker is not a 'series rating', rather all breakers have interrupting ratings, and some of those interrupting ratings are 'series ratings'
Finally if the available short circuit current is greater than the interrupting rating and greater than what the datasheet allows, you have a mis-applied breaker that is not suitable for the application.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Series ratings involve two breakers, one upstream and one downstream, as well as the available fault current the downstream breakers.
There is not much that can be said about a single piece of data.
Series ratings are found in tables not on breaker labels. Either go to the breaker manufacturer's tables on the internet or look for a label in the downstream panel.
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
You changed from a breaker with a 25,000 Amp rating to a 35,000 Amp rating. So if the available fault current is more than 25K and less than 35K, that means you now have a fully rated breaker.
Another possibility is that the fault current is even higher than 35K, and you still have a series rating, but now have a 'correct' one. As @jim dungar says, we can't really tell without more information. But you did up the interrupting rating quite a bit, so that is a strong clue.
Separate issue: In the picture it sure looks like the center conductor is severely heat damaged. That probably needs some looking into.
-Jonathan
So for residential panels, where the main breaker is 22 KAIC and the branch breakers are 10KAIC, is that a series rated system?
If you have a fault with say, 20K amps flowing, is the idea that the main breaker will also open, protecting the branch breaker that can only handle 10K amps?
If you have a fault with say, 20K amps flowing, is the idea that the main breaker will also open, protecting the branch breaker that can only handle 10K amps?
Normally that would be a series rated system but you would need to confirm the exact breakers installed to be sure (the manufacture provides lists showing catalog numbers & amperages). The scenerio you mention is correct.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Actually there is no guarantee that the higher rated breaker clears the fault even if it greater than the AIC rating of the downstream breaker. UL allows either or both breakers to open.
For example: say the downstream breaker has manufacturer test value of 18kAIC but that is not a UL recognized value so the breaker is labeled as only 10kAIC. In a series rating test this breaker could easily clear a fault upto 18kA while the upstream device stays closed.
So what happens if the 10K rated breaker, which can handle 18K opens on a 20K fault and the 22K main breaker does not open?
Does the 18K breaker get, or risk getting, damaged? If the contacts get welded closed the main breaker will open and clear the fault.
Could the branch breaker fail in a catastrophic way? Does series rated breakers guarantee they will not fail clearing a fault, or only that
the fault will be cleared?
Does the 18K breaker get, or risk getting, damaged? If the contacts get welded closed the main breaker will open and clear the fault.
Could the branch breaker fail in a catastrophic way? Does series rated breakers guarantee they will not fail clearing a fault, or only that
the fault will be cleared?
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
UL Series ratings tests do not care which breaker(s) actually clears the fault. Often both breakers open, but that does not mean the fault was actually broken by both.
For true series ratings the breakers do not fail and can be reset.
Strathead
Senior Member
- Location
- Ocala, Florida, USA
- Occupation
- Electrician/Estimator/Project Manager/Superintendent
It is all about the science. As earlier stated, a transformer has a maximum number of amps it can theoretically provide before it physically (scientifically) can't provide any more. Code requires the downstream breakers to be able to handle interrupting this short circuit amps. If a breaker isn't capable, it can explode, or weld together failing to open the circuit, either of which could be seen as a little problem. Any breaker beyond that first breaker must be able to open at the short circuit amps available at it as well. This value goes down relatively quickly because of the resistance of the wire in between. These are requirements.
In many cases, the upstream breaker is able to limit the amount of short circuit current available to downstream breakers to less than the calculated value, because it opens before the value gest that high. In order to be allowed to use this feature in our installation, the manufacturer must have the breakers tested for this function and prove that they are capable of working.
All that said, in your above scenario, there are several different possibilities and we can't just know which is true. First it could be series rating. But the 22KAIC breaker could just have been what was provided and all that was needed was 10KAIC. Or someone could have put the wrong breaker or breakers in the panel.