AIC vs AIR Rating

[stretched2thin]

What is the difference between a magnetic circuit breaker AIC and AIR rating. I see both listed, though I never see them listed together. Is it the same thing?

 

[rbulsara]

yes.

Ampere Interrupting Capacity or Ampere Interrupting Rating.

AIC (or kAIC) is more commonly used in the USA.

 

[jbartos]

Suggestion to stretched2thin (Electrical) Mar 19, 2004 marked ///\\What is the difference between a magnetic circuit breaker AIC
///Supposed to be used for medium voltage circuit breaker or switchgear, e.g. per ANSI C37 series standards.\\ and AIR rating.
///Supposed to be used for low voltage circuit breakers, e.g. per ANSI C37 series standards.\\ I see both listed, though I never see them listed together. Is it the same thing?
///No, it is not. See my comments above. However, many electrical working people often use them interchangeably in the every day electrical parlance, either because of a slip of the tongue or in anticipation that the listener will sort things out on her/his own (not that bad idea to assume other people smarter).\\\

 

[jbartos]

Small encore: Reference: IEEE Std 100-2000 Dictionary
Interrupting rating (protection and coordination of industrial and commercial power systems): A rating based on the highest root-mean-square (RMS) alternating current that the fuse (circuit breaker is forgotten in here) is required to interrupt under the condition specified. The interrupting rating, in itself, has no direct bearing on any current-limiting effect of the fuse.
Interrupting Capacity (packaging machinery). The highest current at rated voltage that the device can interrupt.

 

[rbulsara]

How does a packaging or any other machinery interrupt a current??

A machinary or switchboard or an electrical equipment has what was previously known as short circuit withstand rating or capacity. Now accepted term is SCCR, Short Circuit Current Rating. The amount of short circuit current that the equipment will safely withstand, provided it is protected by a fuse or breaker rated for the Interrunpting Rating of the same amperes.

 

[jbartos]

Comment: The main distinction between Interrupting Rating (IR) and Interrupting Capacity (IC) is in type of current waveforms and associated time instances they are related to by their definitions.
IR is related to the current rms values that cover asymmetry.
IC covers current rms values including asymmetry and peaks, e.g. close and latch. The peak values start being important at medium voltage when the equipment must be able to interrupt and withstand high current peaks without being shattered into pieces by electromagnetic forces. This is beyond the contact current rating since it addresses the mechanical design strength of the device suitable to withstand electromagnetic forces without any damages.

 

[rbulsara]

While I respect some of the above posts trying to differentiate between AIR and AIC based on ‘definitions’ but it must be accepted that in the industry (in the USA), the both terms are used interchangeably and even together. Just look up catalogs of leading manufactures such as Square D, Cutler Hammer or Square D. While term Interrupting Rating is more frequently used for breakers and even defined by NEC, terms such as Interrupting Capacity Rating are also found. Now this may not be acceptable to purists, the point is the answer to the original question is ‘Yes’ for all ‘practical’ purposes as it specifically refers to circuit breakers.

The term AIC (or kAIC) usually been used for specifying Short Circuit withstand rating now being replaced by SCCR in the USA. You will find the ‘AIC’ in abundance in the specifications and shop drawings of the switchboards, bus bracings, etc. and is well accepted by contractors, engineers and manufacturers. Mind you I am only talking about the practices in the USA in the A/E consulting engineering firms.

Please don't get me wrong, I do appreciate all attempts to promote technical 'correctness' in our business but can't be adamant about it.

(Recall 3-way switch? Try specifying a 'single pole double throw' switch and see how many RFI , (Request for Infromation)' you get from the contractors in the USA).

 

[jbartos]

Comment: IR and IC can be used interchangeably on low voltage devices, e.g. fuses, circuit breakers, switches since they are rated on maximum IR rms and the peaks withstand capabilities are built-in by the manufacturer.
Medium and high voltage devices differentiation between rated values and related required capabilities is mandatory. See for example ANSI C37.06-1979, where
current values were discerned for:
1. Max symmetrical Interrupting Capability
2. 3-Second Short-time Current Carrying Capability
3. Closing and Latching Capability 1.6K times Rated Short-Circuit Current.
These ANSI standard practices proliferated into books such as:
Robert W. Smeaton "Switchgear and Control Handbook," 2nd Edition, McGraw-Hill Book Co., 1987.