April 25, 2012
Mr. Dean Wemmer
Pikes Peak Regional Building Department
2880 International Circle
Colorado Springs, CO 80910
Subject: Colorado Springs Utilities change to require a minimum rating of 22 kAIC on service entrance
equipment for residential single phase services.
Dear Mr Dean Wemmer,
Colorado Springs Utilities is making a change to our Electric Line Extension and Service
Standards to require a minimum rating of 22 kAIC (22,000 amps interrupting capability) on service
entrance equipment for all residential single phase electric services. This change is requested to take
effect as soon as practicable, and will be required by January 1, 2013. Please convey this information to
electrical contractors through the Pikes Peak Regional Building Department website if possible.
Fault Current Design Constraints:
The available fault current to service disconnect equipment has been increasing over the years,
exceeding 10 kA (10,000 amps) in many cases, for the following reasons:
 Colorado Springs Utilities typically requires the installation of #4/0 AL triplex secondary
conductor, from the lot corner to the meter, for all new services up to a 200 amp service.
This is a larger size conductor than that used in previous years to accommodate larger
loads and to avoid Voltage Flicker problems.
 We have recently changed our design practices to typically install a 50 kVA transformer
when possible due to the cost savings and increased loading.
 In the past, a typical service drop would have enough impedance to reduce the fault
current to below 10 kA, however, this is no longer the case as shown in the examples
below:
 With the combination of a run of new #4/0 AL triplex secondary conductor, less than forty
feet in total length, and a 50 kVA transformer, the maximum available fault current for a
240 volt phase to phase fault can exceed 10 kA RMS symmetrical.
 If Utilities upgrades an existing 50 kVA transformer to a 75 kVA transformer and the
secondary conductor is a #4/0 AL triplex secondary conductor that is less than sixty five
feet in total length then the maximum available fault current for a 240 volt phase to phase
fault can exceed 10 kA RMS symmetrical.
 Upgrades are frequently required due to increased loading, from improvements such as
air conditioning, hot tubs, PV systems, EV charging stations, etc.
Manufacturer AIC ratings:
From researching manufacturer’s literature, it is apparent that most manufacturers are
standardizing on at least 22 kA ratings for service entrance equipment, and discontinuing products with
the 10 kA rating. All new Square D, Siemens and GE single phase typical residential main circuit breakers
and main breaker load centers come with a minimum 22 kAIC (22,000 amp interrupting capability) rated
main breaker that is series rated with the 10 kAIC branch breakers. Eaton (Cutler Hammer) main circuit
breakers and main breaker load centers still have 10 kAIC, rated versions available, in addition to 22
kAIC and 25 kAIC rated units. Eaton’s BR and CH series have 100A to 125A rated at 10 kAIC, an
optional 100A rated at 22 kAIC, and 150A to 225A rated at minimum 22 kAIC.
Local supply and availability of 22 kAIC main breakers:
A sampling of the electric supply businesses within Colorado Springs were contacted regarding
this issue, and they stock either all 22 kAIC or can easily order 22 kAIC main breakers or main breaker
load centers:
- Quality Electric Distribution sells Siemens with all 22 kAIC main breakers and main breaker load
centers.
- Blazer Electric Supply Co sells GE with a majority of 22 kAIC main breakers and main breaker
load centers. (Modular Metering and Generator panel units are rated at 10 kAIC)
- American Electric Company sells Square D with all 22 kAIC main breakers and main breaker load
centers.
- All Phase Electric sells Eaton (Cutler Hammer) 100A to 125A panels with 10 kAIC, or optional
100A panels with 22 kAIC and 150A to 225A panels with 22 (BR Series) to 35 kAIC (CH Series).
- Graybar sells Square D with all 22 kAIC main breakers and main breaker load centers. Greybar
also sells Midwest Electric Products with 100A to 125A panels with 10 kAIC and 150A to 200A
panels with both 10 kAIC and 22 kAIC.
- Home Depot mainly sells Siemens, GE, Square D, Eaton (Cutler Hammer) and Murray-Siemens
with a majority of 22 kAIC main breakers and main breaker load centers.
- Lowes mainly sells Siemens, GE, Square D, Eaton (Cutler Hammer) and Murray-Siemens with a
majority of 22 kAIC main breakers and main breaker load centers.
10 kAIC vs 22 kAIC price comparison:
The prices are roughly the same for the same type of product between an Eaton 100A main
breaker load centers (10 kAIC) vs Square D, GE and Siemens equivalent versions.
Considerations:
The change from 10 kAIC to 22 kAIC with the manufacturers Square D and Eaton has happened
within the last few years. There are still obsolete 10 kAIC main breakers and main breaker load centers
available for purchase. This change will make 10 kAIC main breakers unacceptable for use, so existing
stock should be used up by the date above on suitable applications.
Other utilities also require the 22 kAIC rating. This insures that service equipment is capable of
handling a short circuit situation, and allows for potential future upgrades. This change also simplifies the
selection of service equipment for electricians, since the 22 kAIC rating is adequate for all 15 through 50
kVA transformer services.
The following table can be used to determine the minimum length of conductor needed for service
entrance cable (#4, #2, and #1/0 are typically used for overhead services, #4/0 and 350 on underground)
when used with 22 kAIC rated equipment:
Meter Sockets are generally not required to be labeled, and one major manufacturer indicated their
product is able to withstand up to 30 kA. Therefore, we do not believe meter sockets are affected by this
change.
Please contact me at 668-4951 with any questions.
Sincerely,
Jonathon O'Donoghue
Colorado Springs Utilities
Engineering Support Coordinator
Engineering Standards
1521 Hancock Expressway, mail code 1812
Colorado Springs, CO 80903
(719) 668-4951