AIC ratings
- Thread starter jociha
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websparky
Senior Member
- Location
- Cleveland, Ohio
Re: AIC ratings
Hi John,
I'm not sure anyone can!
The AIC or AIR ratings are usually determined by the POCO. Currently, there is much debate and back-peddleing over these ratings concerning their acuracy and how it relates to the liability of the "quoted" current.
Hi John,
I'm not sure anyone can!
The AIC or AIR ratings are usually determined by the POCO. Currently, there is much debate and back-peddleing over these ratings concerning their acuracy and how it relates to the liability of the "quoted" current.
- Location
- Illinois
- Occupation
- retired electrician
Re: AIC ratings
You must get the actual KAIC value from the power company. If it's at the service entrance that is where you start, i.e.' 10kaic is quite common for residences and, with the more robust residential distribution systems that are being install be the power companies may be up to 22kaic. Commercial and industrials can be 65-100kaic and possibly more.
But, be that as it may, you must know what the KAIC is at the service entrance first. If your distribution sytem is to be "fully rated" than all of the downstream devices must be rated the same as that of the service entrance.
Should a coordination study be done by a qualified person, the impedance of that distribution system is used to calculate the actual fault current available at a give point in that distribution system and , as such, a device with a lower kaic rating may be applied at that point. That would be a coordinated system as it wouldn't be required to be fully rated. This does save money because devices with lower kaic rating are often less expensive.
If that service entrance feeds a transformer, with the value of the kaic on the primary of the transformer known, the available fault current at the secondary is determined by the KVA of the transformer and its impedance with consideration to motor load contribution. Again, if a coordination study is not done, all of the components must be fully rated for the available fault current available of the secondary of the transformer.
However, in any even, fully rated or coordinated, one must be carefull as a future change in the service entrance or kva of a transformer may result in a change in the available fault current.
You must get the actual KAIC value from the power company. If it's at the service entrance that is where you start, i.e.' 10kaic is quite common for residences and, with the more robust residential distribution systems that are being install be the power companies may be up to 22kaic. Commercial and industrials can be 65-100kaic and possibly more.
But, be that as it may, you must know what the KAIC is at the service entrance first. If your distribution sytem is to be "fully rated" than all of the downstream devices must be rated the same as that of the service entrance.
Should a coordination study be done by a qualified person, the impedance of that distribution system is used to calculate the actual fault current available at a give point in that distribution system and , as such, a device with a lower kaic rating may be applied at that point. That would be a coordinated system as it wouldn't be required to be fully rated. This does save money because devices with lower kaic rating are often less expensive.
If that service entrance feeds a transformer, with the value of the kaic on the primary of the transformer known, the available fault current at the secondary is determined by the KVA of the transformer and its impedance with consideration to motor load contribution. Again, if a coordination study is not done, all of the components must be fully rated for the available fault current available of the secondary of the transformer.
However, in any even, fully rated or coordinated, one must be carefull as a future change in the service entrance or kva of a transformer may result in a change in the available fault current.
ron
Senior Member
- Location
- New York, 40.7514,-73.9925
Re: AIC ratings
Fully rated system means that each device (breaker, fuse etc.) is rated to interrupt or withstand the amount of fault current calculated to be available at that point in the system. Not necessarily rated the same as the transformer secondary available, as that would be a waste of money.
Series rated systems use two devices that have been tested together to create the AIC rating for both devices. Which must be higher than the calculated available fault current at that point in the distribution system.
The pamphlet Don recommended is great for doing manual calcs, although they have you start with an infinite primary calculation for the transformer.
[ April 02, 2004, 09:53 PM: Message edited by: ron ]
Fully rated system means that each device (breaker, fuse etc.) is rated to interrupt or withstand the amount of fault current calculated to be available at that point in the system. Not necessarily rated the same as the transformer secondary available, as that would be a waste of money.
Series rated systems use two devices that have been tested together to create the AIC rating for both devices. Which must be higher than the calculated available fault current at that point in the distribution system.
The pamphlet Don recommended is great for doing manual calcs, although they have you start with an infinite primary calculation for the transformer.
[ April 02, 2004, 09:53 PM: Message edited by: ron ]
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