Breaker upgrade ? Do it with the cheapest ?

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Davebones

Senior Member
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North Of Tampa Fl
Had a arc flash study done on our facility last year . It showed two ( 2 ) 2000 amp main breakers that needed to be upgraded . This is in a 4000 amp SQ D switchgear . Sq d looked at this and gave us a quote to replace and also retro fit the bus to accommodate the new breakers . Being what this is I told my boss I would recommend going with Sq D as it is their type of switchgear . Purchasing is now involved and they want to go online to find someone to do it cheaper . Not thrilled to go with the cheapest when it comes to doing a upgrade like this . Wondered what we should consider when we get quotes to do it cheaper ??
 
Davebones said:
Had a arc flash study done on our facility last year . It showed two ( 2 ) 2000 amp main breakers that needed to be upgraded . This is in a 4000 amp SQ D switchgear . Sq d looked at this and gave us a quote to replace and also retro fit the bus to accommodate the new breakers . Being what this is I told my boss I would recommend going with Sq D as it is their type of switchgear . Purchasing is now involved and they want to go online to find someone to do it cheaper . Not thrilled to go with the cheapest when it comes to doing a upgrade like this . Wondered what we should consider when we get quotes to do it cheaper ??
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Upgraded due to interruption rating being too low? There may be another way, post the specifics of the gear, breaker model, and trip device.
 
The utility upgraded a 1500 kva transformer to 2500 kva . They said our AFC went from 32k to over 53k . These two breakers are only rated 50k ( P frame 2000 amp ) . The ones they recommend replacing them with are ( Power pact R-frame 2000 amp 65 AIC ) .
 
Davebones said:
Had a arc flash study done on our facility last year . It showed two ( 2 ) 2000 amp main breakers that needed to be upgraded . This is in a 4000 amp SQ D switchgear . Sq d looked at this and gave us a quote to replace and also retro fit the bus to accommodate the new breakers . Being what this is I told my boss I would recommend going with Sq D as it is their type of switchgear . Purchasing is now involved and they want to go online to find someone to do it cheaper . Not thrilled to go with the cheapest when it comes to doing a upgrade like this . Wondered what we should consider when we get quotes to do it cheaper ??
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I just saw you response to the previous ppst.
Arc flash? May it be a fault current issue where the KAIC ratings of the breakers in question have to be reconsidered? If so then it may be a bigger issue that is the ratings of the down stream devices where series ratings may be conidered. Just guessing now as changing the breakers I can't see where that would change arc flash as to my understanding an arc flash is as the result of an arcing fault and he hazards ot occurring. Wouldn't it then be a factor of the switchgear design to guard from person injury should one occur?
 
Davebones said:
They said our AFC went from 32k to over 53k .
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I would take a closer look at this information. Is the utility the one telling you its over 53kA? If so what does over 53kA mean (54kA, 59kA, 65kA etc...)?

I would guess that if the utility is providing you with this revised fault current value they are providing it at the secondary terminals of their transformer. If you take the impedance of the service entrance cables into consideration its likely that the available fault current at the switchgear is below 50kA if the secondary fault current at the utility transformer is only slightly above 50ka (IE...53kA).
 
Davebones said:
Sq D did the study . They were the ones that said the breakers now weren't rated for the available fault current at the switchgear .
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Maybe take a closer look at the distance of the service entrance cables to make sure the correct distance was used. Sometimes just a bit longer of a cable distance may bring your fault current down to below equip rating.

Does the facility have a good amount of motors that were considered for the fault analysis?
 
Davebones said:
Sq D did the study . They were the ones that said the breakers now weren't rated for the available fault current at the switchgear .
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Your OP refered to an "arc flash" study which mean sorting competely different to those of us who are familiar with industry. The term was misleading. From your description though it like we guessed that you were really referring to available fault current as compared to the KAIC ratings of the OCPDs.
Basically most should be able to find the worst possible case senario fault current availability are the device entrance by knowing the kva of the transformer based upon an unlimited fault current available at the primary of the transformer. You can get that figurre
If that figue is greater than the service entrance you know you are in deep dodo.
Then you must consider the next higher rated device in then the down sream devices.
If you are still in trouble with the next higher rated device but close it is at that you can get a professional to o a fault system study that would consider what he actual fault current avsilability is at he primary and then consider they fault current is based upon the cable from the transformer world o he device entrance. Such a study is only worth taking the time and expense in doing if here is a need to calculate the actual available fault current.
Then after replacing the main breaker you must evaluate all down stream devices for coordination. If you are blessed you may be we to series rate the down stream devices. Otherwise you will. Have to replace those device to be fully rated or continue. Your coordination study is also to include he down stream devices to see if you are trouble with those OCPDs or not.
 
philly said:
Maybe take a closer look at the distance of the service entrance cables to make sure the correct distance was used. Sometimes just a bit longer of a cable distance may bring your fault current down to below equip rating.

Does the facility have a good amount of motors that were considered for the fault analysis?
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This would seem the cheapest compliant solution. istm the new xrmf is also lower impedance than the old.

Not to be cynical, but would it be outside the realm of possibility that the AIC was calculated just over what the existing breakers are rated for the purpose of selling product?
 
templdl said:
Really?
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It all depends on what the calculated fault current was at each feeder and branch breaker.
If, for example, some were SquareD breakers rated at 10kAIC and the calculated fault current at that location was 15kA, then they might have been compliant originally only because of series rating with the 50kAIC SquareD main breaker upstream.
Replacing that SquareD breaker with one from a different manufacturer would technically invalidate the series rating of the downstream breakers even though they were not changed.
The specific higher AIC SquareD breaker would also have to be series rated with the specific downstream breakers, but there is a good chance that is the case. With a different manufacturer, there is no way that the series rating testing would have been done. However series rating with current limiting fuses is still a possibility.
 
templdl said:
Your OP refered to an "arc flash" study ...
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For Square D, a standard Arc Flash study would include a Short Circuit analysis, to determine the available fault current through out the facility and evaluate if the protective devices have been applied within their ratings. There would have also been a Time Current Coordination study to determine optimum protective device settings. Finally an Arc Flash analysis would have been performed using several different fault current values. assuming of course that the customer was willing to pay for this amount.
 
GoldDigger said:
It all depends on what the calculated fault current was at each feeder and branch breaker.
If, for example, some were SquareD breakers rated at 10kAIC and the calculated fault current at that location was 15kA, then they might have been compliant originally only because of series rating with the 50kAIC SquareD main breaker upstream.
Replacing that SquareD breaker with one from a different manufacturer would technically invalidate the series rating of the downstream breakers even though they were not changed.
The specific higher AIC SquareD breaker would also have to be series rated with the specific downstream breakers, but there is a good chance that is the case. With a different manufacturer, there is no way that the series rating testing would have been done. However series rating with current limiting fuses is still a possibility.
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I didn't realize that after 18 years as a sale and applications engineer for one of the largest molded case breaker manufactures that arc flash was related to fault currnt rating.
News flash, the only time that you have to be concerned ot arc flash is when the available fault current is greater than the kaic ratiing of the device and it tries to interrupt and it explodes.
This is the reason that implant to do a coordination study which should be done by a "qualified.person" such as a PE.
And to guard against an arc flash the electrical equipment has to be designed iwith guards and barriers that meet current arc flash standards.
 
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Davebones said:
The utility upgraded a 1500 kva transformer to 2500 kva . They said our AFC went from 32k to over 53k . These two breakers are only rated 50k ( P frame 2000 amp ) . The ones they recommend replacing them with are ( Power pact R-frame 2000 amp 65 AIC ) .
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If "AFC" means "available fault current", I guess 53kA is too far a stretch! The typical %Z of a 2500 kVA transformer is about 9%. With that percent impedance, you'll get an available fault current of around 45.4kA (including a 100% motor load fault contribution):
FLA = 3007A
Isc = 3007/0.9 = 33,411A
Mot. cont. = 3007/0.25 = 12,028
total = 45,439A ~ 45.4 kA.

With %Z = 8%, the AFC = 49.6 kA
Hope that helps.
 
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templdl said:
News flash, the only time that you have to be concerned ot arc flash is when the available fault current is greater than the kaic ratiing of the device and it tries to interrupt and it explodes.
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That is so incorrect.
 
The study we had done was ( Short - Circuit , Overcurrent Device coordination , & Arc Flash Harzard Analyses ) . These breakers were originally installed in 1984 . My understanding was if the utility hadn't up the size of the transformer from 1500 to 2500 kva we would not have had a issue . We have no issue with the study just concerned about purchasing thinking they can go online and find someone to replace these breakers cheaper . Being this is one of our main services I prefer to think we are better of with the equipment manufacture Sq D services doing this than just anyone that purchasing can get cheaper ...
 
It may be that the report is basing the short circuit value on an infinite bus not the available fault current. I say this because on a 2500kVA transformer the nominal impedance is 5.75% with a tolerance of +/-7.5%. This gives a fault current with an infinite bus a range of 48.6 to 56.7 kA. It may be possible that using the actual available fault current from the utility will result in a value much less than.

I would double check the report to see what value of fault current is being used to determine the overdutied equipment. This should be fairly easy as there should be a table in the report listing the overdutied equipment and the fault current seen by that equipment. This can then be compared to the bolted fault current used at that equipment for the arc flash study. Remember that for design purposes the maximum fault current is used (infinite bus) but for arc flash the actual available fault current from the utility is used. Using the actual fault current may show that the equipment is properly rated for that fault current.

I have seen this before on existing installations that were fine until the loading changed and a new transformer was installed.

For an arc flash study, if there is an overdutied protective device that is doing the interrupting for an arc flash event, that needs to be ignored and the next upstream device used. This usually results in a higher incident energy value than what would be present.
 
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