Series rating dilemma

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ghpham

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Hi all. This is my first post so please take it easy on a newbie :smile:

I'm currently working on a small retail shop and experiencing a problem. The main switchboard (existing) has an AIC rating of 57 KAIC. Using this figure, I arrived at 39KAIC at my 100A, 277/480V panel. Using the calcs., I spec'd the panel with an AIC rating of 42 KAIC. Now, our specifications allowed the panels to be series rated. I recently found out that the contractor has installed a 14 KAIC rated panel. At first glance, I don't believe this will work (not only that, it's not conforming to my design). Unless I can come up with supporting documentation, I believe the project will get red tagged by the electrical inspector. How do I go about checking if this will work or not? (I'm not familiar with series rating).
 
series rating

series rating

If you are depending on series ratings, the panels (breakers) must be of the same manufcturer. If they are, then the supplier (manufacturer) should have the data available to show if the particular style and ampere ratings you have are series rated and to what level.
(for example and EHB 3 pole 50 might siries rate with a KA 3 pole 200, where a EHB 2 pole 100 might no {random numbers})
 
ghpham said:
The main switchboard (existing) has an AIC rating of 57 KAIC. Using this figure, I arrived at 39KAIC at my 100A, 277/480V panel. Using the calcs., I spec'd the panel with an AIC rating of 42 KAIC. [...]the contractor has installed a 14 KAIC rated panel. [...] How do I go about checking if this will work or not? (I'm not familiar with series rating).
Click to expand...

(Please take the below with a large grain of salt. My familiarity with short circuit current and series ratings is all web gathered and _not_ confirmed by professional experience.)

1) The main switchboard should have an AIC rating that _exceeds_ the available short circuit current. You first need to find out the actual available short circuit current available at the panel in question.

2) Series ratings are arrived at by _test_. This means that the particular combination of upstream OCPD and downstream OCPD has actually been tested in a lab to meet certain criteria. You can get series ratings from the various manufacturers, where they will provide lists of the combinations which they've had tested and approved.

3) In addition to the option of replacing the panel, you can add impedance to the panel feeder, for example by running a longer feeder.

-Jon
 
panel

panel

(borrowing Jon's disclaimer, also)
I made no mention of possible remedies, however, since Jon did; I might add to his helpful informantion that the introduction of current-limiting fuses is another possibility to having to replace the panel.
 
augie47 said:
(borrowing Jon's disclaimer, also)
I made no mention of possible remedies, however, since Jon did; I might add to his helpful informantion that the introduction of current-limiting fuses is another possibility to having to replace the panel.
Click to expand...

Unfortunately, no. Current limiting fuses must be used as part of a series rated combination. However the fuse manufacturers want to be able to sell in just this fashion, and so often generate series ratings with downstream breakers from other manufacturers.

-Jon
 
fuses

fuses

and this is prohibited ? reference please
(we just had a major plant inspection with fusible buss plugs used to limit current to the panels..engineered drawings, mfg. submittals..etc....is there a problem?)
 
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Keeping in mind my disclaimer above, my understanding is that current limiting fuses _may_ be used to protect downstream panels, in exactly the fashion that you describe, but that this must be _tested_ as a series rated combination.

The reason for this testing is that fuses and circuit breakers are devices with dynamic impedance that changes in response to an over-current condition. If the downstream device is 'faster' than the upstream device, then it might in some sense 'see' the higher current which it is not capable of interrupting.

This discussion quickly exceeds my training, so I would need to refer you to past discussions and other board members with greater expertise: (I've participated in some of the below, and present my understanding of the situation at the time, but I've learned lots from these discussions:)
http://forums.mikeholt.com/showthread.php?t=87880
http://forums.mikeholt.com/showthread.php?t=86837
http://forums.mikeholt.com/showthread.php?t=85209
http://forums.mikeholt.com/showthread.php?t=83722

-Jon
 
ghpham said:
I'm currently working on a small retail shop and experiencing a problem. The main switchboard (existing) has an AIC rating of 57 KAIC.
Click to expand...
That Information is worthless. The contractor may have have that panel
available and used it. You need the available fault current from the utility.

augie47 said:
and this is prohibited ? reference please
(we just had a major plant inspection with fusible buss plugs used to limit current to the panels..engineered drawings, mfg. submittals..etc....is there a problem?)
Click to expand...
This method may protect the panels but not the breakers in the panel. If you have a down stream fault, the fuse and breaker will attempt to interrupt the fault at the same time. The fuse and breakers must both be series rated.
 
augie47,
(we just had a major plant inspection with fusible buss plugs used to limit current to the panels..engineered drawings, mfg. submittals..etc....is there a problem?)
Click to expand...
240.86(A) would permit this, but in many plants there would be a problem with 240.86(C).
Don
 
thanks for the reply all. Perhaps I should clarify the best I can.

1. The building shell engineered did the calculation and figured the available ISC at the main switchboard is 57KAIC. The switchboard should then be 65KAIC (the next level). However, to continue my calculation, should I not use 57KAIC?

2. The OCPD at the switchboard to the panel is a fuse. The plan checker indicates he will not allow let thru as part of the calc. so then should I use 57KAIC at the fuse and continue my calc.?

3. The panel downstream is MLO, so if the contractor chose 14KAIC as the rating for the breaker, I would need to: ascertain that main switchboard, fuse, panel and breaker is from the same manufacturer.

4. If I choose to use series rating in the future, I then would need to specify specific manufacturer products for all components? In a bidding situation, that would not be the case. What would I need to submit to the city if they ask for cut sheets etc. if the project is still in bid.

thanks all.
 
ghpham said:
1. The building shell engineered did the calculation and figured the available ISC at the main switchboard is 57KAIC. The switchboard should then be 65KAIC (the next level). However, to continue my calculation, should I not use 57KAIC?
Click to expand...

Numerically correct. I believe that you have a terminology confusion here. The available short circuit current is 57KA, and you should use that in your calculations. The interrupting rating is 65KA.

ghpham said:
2. The OCPD at the switchboard to the panel is a fuse. The plan checker indicates he will not allow let thru as part of the calc. so then should I use 57KAIC at the fuse and continue my calc.?
Click to expand...

Again correct.

ghpham said:
3. The panel downstream is MLO, so if the contractor chose 14KAIC as the rating for the breaker, I would need to: ascertain that main switchboard, fuse, panel and breaker is from the same manufacturer.
Click to expand...

Not quite correct but often the case.

You would need to ascertain that they were part of a recognized series rating. Series ratings require actual _testing_ of the equipment. Because series ratings are paid for by manufacturers who want to sell their equipment, it is _generally_ the case that the components of a series rated set would be from a single manufacturer.

But this is not necessarily the case. In particular, fuse manufacturers want to sell fuses for just this application, and I recall seeing a lists of series rated equipment where the upstream device was from a fuse manufacturer and the downstream devices were from a circuit breaker manufacturer. Also in theory you could pay UL or some other testing lab to test out the exact combination of devices that you have to demonstrate a proper series rating.

-Jon
 
For you to determine if you already have Series Rating, you need to get the model & amperage of the breaker & fuse.
http://www.cooperbussmann.com/2/SeriesRatings.html
If I choose to use series rating in the future, I then would need to specify specific manufacturer products for all components? In a bidding situation, that would not be the case. What would I need to submit to the city if they ask for cut sheets etc. if the project is still in bid
Click to expand...
You would need to specify the manufacturers for the breaker and the fuse, only.
In a bidding situation, you can NOT substitute either manufacturer and yes cut sheets are acceptable.
Just my $.02
 
did your spec allow for series rating as long as the contractor provided sufficient documentation that all the equipment is listed as a series rated system?
 
UL testing for series combinations of fuse and circuit breaker are independent of the fuse manufacturer. These fuse-breaker tests must be performed using a generic "umbrella" fuse.

UL testing for series combinations of circuit breakers requires the exact models of breakers to be tested. For this reason very few (if any) manufacturers have tested their breakers with those of other manufacturers.

Your specs allowed series ratings. You just need the contractor to provide a copy of the series tested ratings for the panel involved. Almost every panelboard manufacturer has some of this infomation in their normal catalog.
 
Thanks all, for your help. I have another question. What is the interpretation of the following:

"Motor circuit protectors shall not be used as part of a series combination interrupting rating."
 
Sorry I forgot to post this origionally. In addition to all the above posts, remember you can NOT use Series Rating if the sum of motor full load currents exceeds 1% of the load side (protected) circuit breaker?s individual interrupting rating.
Just my $.02
 
davidr43229 said:
The NEC does require it within sections 430.40, 430.52, 430.53 & 430.55
Just my $.02
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I don't see it in any of those sections. Maybe you can point out just where you think single phasing protection is required in any of them.
 
davidr43229 said:
In a single phase condition the other 2 legs go up 197% in current, which is an overload. These sections address overloads or OCPD sizing to prevent damage in just this sort of event.

Just my $.02
Click to expand...

I have seen them run single phase for hours without tripping anything if they are lightly loaded. you are not describing a requirement, more like a side benefit. I like the IEC overloads because normally single phasing protection is built in to those units.
 
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