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#195572 - 08/11/10 01:54 PM Need help learning about KAIC ratings and calcs.
wewire2 Offline
Member

Registered: 11/14/02
Posts: 246
Loc: California
I'm looking for "Understanding everything there is to know about KAIC ratings and calculations for dummies." Any good suggestions on where to find some help learning this stuff
without having to be a rocket scientist? (which I'm not!)
Thx!

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#195576 - 08/12/10 09:19 AM Re: Need help learning about KAIC ratings and calcs. [Re: wewire2]
sabrown Offline
Member

Registered: 12/12/02
Posts: 297
Loc: Ogden, Utah, USA
Cooper Busmann has/had a bulletin EPR-1 called "Electrical Plan Review Short-Circuit Currents, Interupting Ratings, and Current Limitation" which goes through a simplified method. Mike Holt also has/had an excel spreadsheet that used the same or similar method.

Neither of these methods is great but will get you ballpark often and if you are well within the rating of the equipment you are likely OK. Neither are good for ArcFault studies. The Rocket Scientist method also takes into account the inductance of the source each step of the way (not just the inductance of that point your are studying)and results in higher levels of fault current available. To learn about this bettter method you could take a course from www.brainfiller.com. Another option is purchasing expensive software, which I have neve bothered with due to budget.

Shane

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#195578 - 08/12/10 12:50 PM Re: Need help learning about KAIC ratings and calcs. [Re: sabrown]
HotLine1 Online   content

Member

Registered: 04/03/02
Posts: 6804
Loc: Brick, NJ USA
Ditto on what Shane said about Bussmann info. It's available at there website, & I use it within my courses at Vo-Tech. It's not 'perfect' by EE/PE standards but works basically good enough to be acceptable in a lot of jurisdictions.
_________________________
John

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#195579 - 08/12/10 01:00 PM Re: Need help learning about KAIC ratings and calcs. [Re: sabrown]
wewire2 Offline
Member

Registered: 11/14/02
Posts: 246
Loc: California
I found the link.
http://www.bussmann.com/library/docs/EPR_Booklet.pdf
Seems like a great start and better than anything I
have found so far. Stay tuned for a zillion questions!
Haha Kidding! Thanks for the input!

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#195583 - 08/12/10 04:36 PM Re: Need help learning about KAIC ratings and calcs. [Re: wewire2]
JBD Offline
Member

Registered: 07/12/01
Posts: 599
Loc: WI, USA
The Bussmann literature is extremely good for the basic of short circuits, however it is very biased against circuit breakers.

Most of their examples involve relatively high fault currents. In the real world many circuits, other than service entrances, often do not have enough SCA (especially during arcing faults)to have fuses operate in their current limiting region.

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#195586 - 08/12/10 07:10 PM Re: Need help learning about KAIC ratings and calcs. [Re: JBD]
HotLine1 Online   content

Member

Registered: 04/03/02
Posts: 6804
Loc: Brick, NJ USA
JBD:
Yes, Bussmann 'favors' fuses, because that is their business, and of the high AIC ratings.

That said, I have to express the following, regarding Bussmann.

Here in NJ, two (2) of Bussmanns PEs are instructors that do NJ DCA CEU seminars for us AHJs. They tag team a in-depth presentation using PowerPoint based on the 'Plan Review' booklet, the 'Point to Point' calculations, and other company literature. This is a 6 hour CEU course, and most AHJ's that I know thought it was good+ to excellent.

The book (Plan Review) and other related literature used to be available for 'free', but within the last year or so required either a download, or purchase a hard copy.

They also have a program called 'Safety Basics' which is available to qualified trade instructors, including PowerPoint and DVD video. I find that to be a useful tool for my entry level Vo-tech classes, as it shows some very interesting faults, and the results.

As I said above, there business is fuses. They show CB's within the Safety video, and discuss the cost differences between CB's and fuses based on the AIC ratings.



Edited by HotLine1 (08/12/10 07:12 PM)
_________________________
John

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#195644 - 08/16/10 10:16 AM Re: Need help learning about KAIC ratings and calcs. [Re: HotLine1]
Scott35 Offline

Broom Pusher and
Member

Registered: 10/19/00
Posts: 2724
Loc: Anaheim, CA. USA
wewire2;

The Bussman Literature is very helpful, and will assist you greatly in covering the Basics per SCA Rocket Sciences.
(SCA = Short Circuit Amperes)

Even though Bussman is quite biased towards Fuses, the Documents contain lots of good data - including time-Trip Current Curves, and of course, SCA Calcs.

The SCA Document describes three methods of Fault Level Calcs:
Ohmic, Per-Unit, and Point-To-Point.
Point-To-Point method is least accurate, but is simple to use, and accepted by most DBS (Building Departments).

Abridged description for any Fault calcs...

  1. Obtain Fault Quote from Utility Service Engineers. This will give you the Base level of SCA available at the Service Equipment - or, more precisely, at the Line Side of the Service Disconnect.
    (more on this later).
  2. Motor Contributions to Faults... Add all Motors' LRA (Locked Rotor Amperes) to the available SCA at the Service Equipment.
    This adjusted level is what you use as the "Total Available SCA" on the "Load Side" of the Service Disconnect.
    Designate the Switchboard directly connected to the Service Section as the "Main Switchboard", or "MSB".
  3. Using the Total SCA Available (per line #2 above), Fault Levels "Downstream" from the Main Switchboard are figured per run types, lengths and Conductor Reactance (X) / Resistance (R).
  4. For Transformers (Separately Derived Systems), the SCA available at the Primary is figured; then that value is used to compile the SCA available at the Secondary.
    Afterward, the new SCA (available at the Secondary) is used to figure "Downstream" Fault Levels, similar to that described in #3 above.


Notes per Line #1:

a: Optional SCA from Utility - if no quote may be obtained, obtain Transformer Capacity + %Z (Impedance) per Nameplate Data, determine SCA at Secondary Terminals, apply this to the Service Feeders' data (Conductor type, length, X/R).
Best to request Fault Quote from the Utility Service Engineers / Planning Staff.

b: Motor LRA Contributions may be added in where their Circuits derive (at Panelboards, Transformer Secondary Feeders, etc.), or at the MSB.

c: The AIC (Interrupting Capacity) of all devices in the Service Section + MSB needs to be no less than the available SCA.
For example, if the available SCA is 10,100 Amps, the minimum AIC for the Devices will be 14,000 Amps.

..............................................

When compiling a Series Rated System:

All Devices will be listed per the Manufacture's Series Rating Compatibility listings.
Combinations will be given per "Upstream" device type, protecting "Downstream" device types, with a maximum Interrupting Rating (AIR) -vs- System Voltage and Phases.

This allows a Downstream Device with an AIC rating lower than what is available, to be protected by an Upstream device with an AIC rating above the available SCA at the Upstream device.

Fully Rated Systems use devices with AIC / AIR ratings, which are greater than or equal to the available SCA at the device.

Good luck, and feel free to ask any questions that surface!

Scott
_________________________
Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

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#195665 - 08/17/10 11:03 AM Re: Need help learning about KAIC ratings and calcs. [Re: Scott35]
wewire2 Offline
Member

Registered: 11/14/02
Posts: 246
Loc: California
Thanks Scott. Very helpful tips! Getting the info from the utility in a timely manner is usually an issue. Rarely do the EE's calc the system out on the plans. The inspectors rarely if ever even pay attention to the SCA when inspecting. If there is an accident (Murphy's law) down the road there's a good chance the installer is likely to get hit along with the designer by the lawyers. Should be the EE's responsiblity since they don't pay us to design. Also, it's amazing how many mistakes some EE's make on the plans. You ever notice that?

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#195667 - 08/17/10 11:30 AM Re: Need help learning about KAIC ratings and calcs. [Re: wewire2]
HotLine1 Online   content

Member

Registered: 04/03/02
Posts: 6804
Loc: Brick, NJ USA
Yes, errors do happen in the best set of Plans submitted for Plan Review/Plan Check. My SOP for errors is a written rejection letter to the EE/PE &/or Architect of record.

Missing calcs & typo's are common.

BTW, back on track of this thread, there are 'common' transformer AIC's within the Bussmann literature for the point-to-point calcs.
_________________________
John

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#195708 - 08/18/10 10:08 PM Re: Need help learning about KAIC ratings and calcs. [Re: HotLine1]
JBD Offline
Member

Registered: 07/12/01
Posts: 599
Loc: WI, USA
Originally Posted By: HotLine1
BTW, back on track of this thread, there are 'common' transformer AIC's within the Bussmann literature for the point-to-point calcs.


I am sure you meant to say 'there are common transformer SCA's'. AIC is an abreviation of Amps Interrupting Capacity and only applies to protective devices which clear fault currents.

Of course Bussmann's business is fuses, but some of their information on circuit breakers borders on the edge of being misleading. I just wanted the OP to be aware of this issue.

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