Series Ratings on Equipment and Breakers

[TALO]

Hello all,

I have a couple questions on the series rated equipment...

If we have a transformer feeding a building with an available fault current of 18,000 amps and wanted to go with a series-rated system rather than fully-rated, is it acceptable to use a disconnect with fuses rated at 200kAIC feeding a main breaker rated at 25kAIC, where the rest of the breakers in the panel are only rated 14kAIC?

The way I understand it, the panel guts would also need to be rated above the available 18k (so as not to explode before hitting the main breaker), but I'm having some difficulties finding this rating on any guts.

Another note, the fuses (rated at 200kAIC) have a peak let through current of 9k amps, so would this mean I don't have to worry about the rating on my panel (assuming it can withstand at least the 14k my branch circuit breakers are rated for)?

Lastly, the NEC says that a series rated system must either be engineered, or the equipment tested and marked for such use. Would this be a testing facility that I literally send my equipment in to be tested, or are the kAIC ratings on the fuses/breakers sufficient?

Thanks in advance for your responses!

 

[augie47]

Series rated installations are very common. 240.86 sets the requirements for such a system.
Commonly one can use the manufacturers data to show a series rated system is in compliance.
The manufacturers can provide data to show an individual breaker is ratwed to a certain point provided it is in series with a specific breaker or fuse,
In you post, the 14k breakers would need to be series rated by use of the specific 25k main or the fuse ahead of the panel.
Beyond using manufacturers data you can use the services of a professional engineer to show the system is properly rated and such services are required when you have such things as large motor contributions.

 

[TALO]

Thanks for the reply. I apologize for posting my question before thoroughly searching through old posts. I was able to find some very useful information in the archives.

I found the Eaton series rating information manual and I understand this much better now.

Thanks again!

 

[templdl]

Thanks for the reply. I apologize for posting my question before thoroughly searching through old posts. I was able to find some very useful information in the archives.

I found the Eaton series rating information manual and I understand this much better now.

Thanks again!

Yes, you located the mother load. EATON has an excellent number of charts that show what combination of their breakers have a listed series tasting as well as with fusesd. One thing to keep in mind is that you can not mix manufacturers breakers and expect to end up with series ratings.

 

[GoldDigger]

One thing to keep in mind is that you can not mix manufacturers breakers and expect to end up with series ratings.

Not that there would be any intrinsic problem with the operation, of course, but there is less than zero motivation to perform the hundreds or thousands of expensive tests required for listing with another manufacturer's equipment.

 

[templdl]

Not that there would be any intrinsic problem with the operation, of course, b

Is this asn opinion or what basis do you make this statement? It could be misleading. Series rating must me tested and to assume that tthere would not be any intrinsic problem who would assume the liability based upon this opinion? I personally would not want to rely on theory and stick with UL listed series rated devices.

 

[GoldDigger]

Is this asn opinion or what basis do you make this statement? It could be misleading. Series rating must me tested and to assume that tthere would not be any intrinsic problem who would assume the liability based upon this opinion? I personally would not want to rely on theory and stick with UL listed series rated devices.

It is an opinion, of course.
My real point was that whether it would be safe or not, the NEC will not allow it without tests.
It is, IMHO, also true that the interaction between time curves and construction details is so complex that it is definitely not good enough just to say that an untested combination is "equivalent to" a tested combo based only on nominal specs.

 

[topgone]

It is an opinion, of course.
My real point was that whether it would be safe or not, the NEC will not allow it without tests.
It is, IMHO, also true that the interaction between time curves and construction details is so complex that it is definitely not good enough just to say that an untested combination is "equivalent to" a tested combo based only on nominal specs.

If my memory serves me right, the provision on "series-rating" was included in the NEC to provide a workable solution to load centers with available fault currents exceeding the original design levels (addition of motor loads; current carrying capacities are within the feeder capacities but the fault levels are higher).

The basic assumption is that the under-rated equipment must remain passive during the fault and the equipment with higher fault current rating will clear the fault. The only thing those criteria will be assured is for combo-testings to be done. Breaker manufacturers list breaker combinations that they have "tested". But if you are in the design stage, why go for "series-rated" when you can "design" properly? It's not there yet, that is!

 

[Haji]

If you are in the design stage, why go for "series-rated" ?!

Potential cost saving of series rated breakers over fully rated breakers.:happyyes:

 

[GoldDigger]

Potential cost saving of series rated breakers over fully rated breakers.:happyyes:

And also just availability in the size and shape you need.

 

[Haji]

Manufacturers such as GE are the best people to consult for all that.

 

[templdl]

If my memory serves me right, the provision on "series-rating" was included in the NEC to provide a workable solution to load centers with available fault currents exceeding the original design levels (addition of motor loads; current carrying capacities are within the feeder capacities but the fault levels are higher).

The basic assumption is that the under-rated equipment must remain passive during the fault and the equipment with higher fault current rating will clear the fault. The only thing those criteria will be assured is for combo-testings to be done. Breaker manufacturers list breaker combinations that they have "tested". But if you are in the design stage, why go for "series-rated" when you can "design" properly? It's not there yet, that is!

Yes, it comes down to a breakers current limiting capability. All breasker have as ome degree of current limiting caspability which relates to the speed at which the contacts oped amnd clear an arc limiting the let through current to down stream devices. It is this characteristic that allows for them to be series rated but only when an actual series rating test is done that incorporate the devices to be used in series. The use of TC curves to determine let through current may provide information that would lead to an assumption but that does not substitute for an actual series test. TC curves often provide data that ican be used to determine if a device is suitable to pass an actual series test.

 

[TALO]

But if you are in the design stage, why go for "series-rated" when you can "design" properly? It's not there yet, that is!

In this case (200a 480v panel) going with a series rated system is saving thousands of dollars. My quote for fully-rated panelboard and breakers was around $4500, built by the manufacturer 4-6 weeks out (to get it next week, the price goes up to $10k). Where as the series-rated equipment is in stock at my supply house.

 

[topgone]

In this case (200a 480v panel) going with a series rated system is saving thousands of dollars. My quote for fully-rated panelboard and breakers was around $4500, built by the manufacturer 4-6 weeks out (to get it next week, the price goes up to $10k). Where as the series-rated equipment is in stock at my supply house.

IMO, it all boils down on whether or not that $5000 savings can offset possible foregone income should your panelboard be used in a process control environment and the series-rated breakers do not selectively coordinate. Using series-rated breakers means you are designing the upstream breaker to protect the lower-rated downstream breaker's load when fault happens on that feeder. It's safe but not desirable. Been there, got burned with series-rated decisions. Sometimes, customers are not so forgiving when it comes to losing money. But it's still your call.

 

[mayanees]

240.86(C)

240.86(C)

Make sure the panel CAN be used in a series-rated application and isn't excluded due to motor contributions. The amount of motors allowed on the panel is less than 1 percent of the lower-rated device, so at 10kA, that's only 100 amps of motor load. I guess that's probably a lot on a 200-amp panel!