Series Vs. Fully rated

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coulter

Senior Member
Mike01 said:
... One last thing when looking at an existing installation in the field is there any easy way to tell if the existing system is series or fully rated??

Mike-
Check the available SCC and the rating of the next two inline CBs.

Check the UL listing. No guarentees on this one. NEC allows (has alllowed) unlisted, engineered combinations.

carl
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
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Electrical Contractor
Series-rated systems are supposed to be field-labeled so that proper fuse/breaker/parts replacements can be made while maintaining the required protection levels.
 

BAHTAH

Senior Member
Location
United States
Series Rating

Series Rating

What are some of the advantages / disadvantages to fully vs series rated why select one over the other? Just curious on your opinions...

You should take a look at 240.86, specifically (C). If you have an industrial installation then athe ability to Serie Rate may become an issue with respect to motor load contribution. Installations where motors may be added in the future could cause problems.

If you have an installation where it is possible that someone (???) may change out a breaker and void the series rating then I would say using series ratings would not be a good idea.

If you have an installation that is fixed in its design, such as an office where no expansion would cause an issue with the series rating, then I would say it would be ok to do so. In my opinion series rating between a main breaker and those in the same switchboard or between a feeder breaker and a main breaker in a panel would be the safest applications depending upon the installation conditions. I think the main problem is what may happen to the system after the initial installation and what possibilites there are for someone voiding the initial series rating by changing out a breaker without paying attention to what should be used as the replacement.
 

ryan_618

Senior Member
Mike01 said:
Ok, I am starting to understand the difference, does anyone know where I can find some good literature comparing the two system...
That is the tought part...do you want it with a biased circuit breaker slant, or a biased fuse slant?

It seems really difficult to me to find information that doesn't try to hype one and degrade the other.
 

roger

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ryan_618 said:
It seems really difficult to me to find information that doesn't try to hype one and degrade the other.

With the exception of discussions such as these, that has been my observation as well.

Roger
 

chris kennedy

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60 yr old tool twisting electrician
I've had a real problem in the past couple years both researching and understanding coordination. For what its worth and I'm sure a lot of you are familiar with Bussman's site. Here is a quote:
"The unlatching time indicates the point at which the breaker senses an overcurrent in the instantaneous region and releases the latch holding the contacts. However, the fault current continues to flow through the breaker and the circuit to the point of fault until the contacts can physically separate and extinguish the arc." " The relatively long time between unlatching and the actual interrupting of the overcurrent in the instantaneous region is the primary reason that molded case circuit are very difficult to coordinate."
So before breaker 1 unlatches breaker 2 can sense enough current to begin unlatching.
 

roger

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I think that thread just reinforces the breakers verses fuses (us against them) argument. Sq D provides their information and then your Bussman info seems to imply (with out directly saying it) that only fuses can acheive this. :)

Roger
 

davidr43229

Senior Member
Location
Columbus, Oh
think that thread just reinforces the breakers verses fuses (us against them) argument. Sq D provides their information and then your Bussman info seems to imply (with out directly saying it) that only fuses can acheive this
Roger, from a personal standpoint, not at all :smile: I read the Article and the point being, you MUST BE Carefull which system you choose and know all Systems are not created equal.
Bussman +n
Just my $.02 (ducks)
 

don_resqcapt19

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Bussman info seems to imply (with out directly saying it) that only fuses can acheive this.
That is the reason that they submitted the proposals that resulted in 700.27 and 701.18:grin:
 

davidr43229

Senior Member
Location
Columbus, Oh
That is the reason that they submitted the proposals that resulted in 700.27 and 701.18
Please don't forget 517.26, 700.4, 700.9(B), 700.9(C) and 700.16 The objective of these requirements is to ensure system uptime with a goal of safety of human life during emergencies or for essential heath care functions and a preparedness for any other 911 incident and panic control.
There was a flaw with the NFPA-110 article. Regardless of how you achieve this or what you assume to be the case, these code articles were long overdue and approved and embraced by the other panel members as well as the General Assembly. Would you fault Bussman+n for this also ?
We may take many different roads to achieve the same goal.
Just my $.02
 

jim dungar

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don_resqcapt19 said:
That is the reason that they submitted the proposals that resulted in 700.27 and 701.18:grin:

One word of warning when using fuse slectivity tables supplied by a manufacturer: they are only valid for the specific fuses in the table. If the customer decides to replace a fuse from brand XX with one from brand YY then the selective coordination may no longer exist.

In my gut, I feel that for branch circuits many facilities will eventually install a less expensive fuse or whatever breaker is "on the shelf". Because of this I do use series-ratings.
 

SoonerinNeb

New member
Location
Nebraska
QUOTE]In my gut, I feel that for branch circuits many facilities will eventually install a less expensive fuse or whatever breaker is "on the shelf". Because of this I do use series-ratings.[/QUOTE]

Jim, did you mean to say that you do not use series-ratings?
 

davidr43229

Senior Member
Location
Columbus, Oh
Jim,
In my gut, I feel that for branch circuits many facilities will eventually install a less expensive fuse or whatever breaker is "on the shelf". Because of this I do use series-ratings.
I suspect you meant to say "Not"...In the course of my daily travels I see this alot, in regards to Series Rating and Arc Flash. A different manufacturer will come in with a hot price and purchasing wants to change the brand & Maintainence says "ok", they have no clue what they have just done. Altered Series Rating, altered Arc Flash calcs (sometimes) and mucked up their overall coordination. I also see maintainence facilities stocking an RK-5 30 amp fuse along with a RK-1 30 amp fuse, right in the same bin.
Just my $.02
 

jim dungar

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SoonerinNeb said:
Jim, did you mean to say that you do not use series-ratings?

I do use series-ratings. I think they can prevent a lot of misapplications especially in residential and commercial settings. Most electricians do not bother to see if a panel is series-rated or fully-rated before they install a new branch breaker (I worked for an electrical distributor for many years, <10% of the time was AIC ever mentioned for replacement breakers). If I can, I engineer a series rating so that all of the L&A branch breakers (the ones most likely to be replaced) are of a "standard, off the shelf" AIC rating.
 

jim dungar

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There is no one right method. Each and every installation needs to be evaluated completely.

In general, there are only a few things that you can do to mess up a series rating that uses standard AIC breakers. One is to change the feeder/main device - not likely to happen, but possible. Another is to add motor loads that exceed 10% of the AIC rating of downstream breaker (100A for a 10kAIC breaker) - not likely to happen in a 200A panel. About the most likely occurence would be the use of a "classified" branch breaker or a design change by the original manufacturer.

But, it is very easy to mess up a fully rated system simply by putting in the wrong branch breaker. I would guess that more than 25% of the "arc flash" studies I have done, have found standard AIC breakers installed in panels alongside of high AIC devices.
 

davidr43229

Senior Member
Location
Columbus, Oh
Another is to add motor loads that exceed 10% of the AIC rating of downstream breaker
Series rated combinations shall not be used where the sum of motor full load currents exceeds 1% of the load side (protected) circuit breaker's individual interrupting rating.
Juts my $.02
 

jim dungar

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davidr43229 said:
Series rated combinations shall not be used where the sum of motor full load currents exceeds 1% of the load side (protected) circuit breaker's individual interrupting rating.
Juts my $.02

Major Oops.

You are correct at 1%, I had it in my head 100A max motor load for 10kAIC breaker.
 

MO_EE

Member
The statement "selective coordination can be probabilistic but cannot be guaranteed." should make you a little wary of this situation.

To be truely coordinated you cannot take the probabilites of fault locations and associated levels into consideration. The system must be analyzed as if the fault is directly on the load side of the downstream breaker. In this case the fault current is going to be greater than what the breaker is rated for (hence the series rating.) If the upstream device does not open then the downstream breaker will see more fault current than it's rated for and could result in failure. Fully Rated systems are the way to go if it is feasible, otherwise system selective coordination could be compromised.
 
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