EASA’s “Recommended Practice for the Repair of Rotating Electrical Apparatus” is designated ANSI/EASA AR100 and was first approved as an American National standard in 1998. Since then, it has been revised and approved five more times, in 2001, 2006, 2010, 2015, 2020 and now in 2025.
ANSI/EASA AR100 is a must-have guide to the repair of rotating electrical machines. Its purpose is to establish recommended practices in each step of the rotating electrical apparatus rewinding and rebuilding processes.
The scope of this document describes record keeping, tests, analysis and general guidelines for the repair of induction, synchronous and direct current rotating electrical apparatus. It is not intended to take the place of the customer's or the machine manufacturer's specific instructions or specifications or specific accepted and applicable industry standards or recommended practices.
This document should be supplemented by additional requirements applicable to specialized rotating electrical apparatus including, but not limited to, listed explosion-proof, dust-ignition proof, and other listed machines for hazardous locations; and specific or additional requirements for hermetic motors, hydrogen-cooled machines, submersible motors, traction motors, or Class 1E nuclear service motors.
ANSI recognizes only one standard on a topic; therefore, ANSI/EASA AR100 is the American standard for repair of rotating electrical apparatus.The Recommended Practice is an important publication to distribute both internally and to customers.
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Approval Process
The EASA Technical Services Committee (TSC) reviews the recommended practice and proposes changes; a consensus body group (formerly termed a canvass group) approves and often comments on the TSC proposals. The consensus body group has representation from service centers (producers), end users and those with a general interest. Per American National Standards Institute (ANSI) requirements, there must be balanced representation among the consensus body group representatives. After the consensus body group and the TSC find consensus agreement, the revised document is approved by the EASA Board of Directors. Following Board approval, ANSI is requested to approve the revision as an American National Standard. The entire process must be completed within five years following the previous revision.
What’s New in 2025?
The 2025 edition of AR100 contains 72 revisions, 48 substantive (technical) and 24 editorial. Here, we will focus on the more significant changes, noted in clause order, and some of the reasons for making these changes.
The only revision to AR100 that affected the Accreditation Program Checklist
was to clause 3.11. |
1.1 Purpose
Added the sentence “Although repairs are normally performed in a service center, this document also applies to onsite repairs.” This clarifies that AR100 applies to onsite as well as service center repairs.
1.4 Condition Assessment and Failure Investigation
The use of photography was added with the sentence “Photographs of all sides of the equipment can be useful in recording the general condition of the equipment as received, the placement of accessories and machine configuration for records and for comparison during the final inspection of the completed repair.” This not only acknowledges that photography should be used, it provides rationale for using it.
1.8 Terminal Leads
Added a sentence describing what to do if customer lead markings differ from NEMA or IEC standards. This is also the first location in the document with reference to the standard NEMA MG 00001, the successor to NEMA MG 1.
2.1.2 Permissible Runout
Permissible shaft extension runout tolerance Tables 2-3 (NEMA machines) and 2-4 (IEC machines) replaced with Table 2-3 “RPM versus Allowable Total Indicated Runout. The runout tables from NEMA and IEC were based on shaft dimensions, and the replacement table is more practical and simpler to use, with tolerances based on shaft speed.
2.2.2.1 Sleeve Bearing End-Thrust
Expanded on the topic of sleeve bearing end-thrust to include use of limited end float couplings and added a new table with tolerances for end play and rotor float designated Table 2-8 “End Play and Rotor Float for Coupled Sleeve Bearing Horizontal Motors”.
2.5 Laminated Cores
A good practice action item was provided by adding the sentence “If evidence of hot spots is noted, perform a core loss test.”
2.5.1 Rotating Elements
Separate runout tolerances for 2 pole and for 4 or more pole machines are provided in the two sentences “The runout of the rotating element core outside diameter relative to the bearing journals should not exceed 5 percent of the average radial air gap for machines with 4 or more poles. For 2 pole machines the runout should not exceed 0.003” (0.08 mm).” The previous edition used a single tolerance regardless of poles.
2.7 Slip Rings
Added a tolerance for maximum total indicated runout for speeds below 2500 ft/min (760 m/min) as well as for speeds below 5000 ft/min (1525 m/min) and for greater than 5000 ft/min (1525 m/min). The previous edition provided two tolerances, one for speeds below 5000 ft/min (1525 m/min) and one for greater than 5000 ft/min (1525 m/min).
2.8.2 Undercutting and beveling
Provides a good practice method for chamfering commutator bars with the statement “Both edges of each bar should be chamfered, either by hand-chamfering or by nylon brush designed for that purpose. This minimizes brush chatter and noise in operation, and extends brush life.”
2.11 Brush Setting for DC Machines
A good practice action item was provided indicating to add equalizing jumpers to all brush posts of DC machines that lack them with the statement “Brush posts of the same polarity should have equalizing jumpers connecting them. This applies to positive as well as negative brush posts.” Doing so reduces the likelihood of sparking at the brushes due to unequal voltage at brush posts of the same polarity.
3.3 Stripping of Windings
The sentence “Core temperature should be controlled to avoid degradation of the interlaminar insulation and distortion of any parts” was revised to “Core temperature should be controlled to avoid degradation of the interlaminar insulation and distortion of the stator frame.” The change provides focus and clarifies that core temperature control is intended to avoid distortion of the stator frame.
3.6 Stator, Rotor and Armature Coils
Good practice action item added regarding replacing surge rings with sentence “Surge rings or similar supports should be replaced as found.”
3.6.2 Form-Wound Coils
To harmonize with the change made in clause 3.6 the sentence “Surge rings or similar supports should be secured to the coils and the coils laced to one another as necessary to minimize coil distortion and movement” was deleted.
3.7.1 Stationary Coils
In addition to varnish treatment and vacuum pressure impregnation of stationary field coils, the wet winding method was added to indicate that it is also a treatment option.
3.8 Squirrel Cage and Amortisseur Windings
To help prevent performance issues with motors and generators, particularly when starting, the following caution was added “Synchronous rotors often have amortisseur bars of different materials.”
3.9 Shaping and Lacing of Stator Windings
Good practice guidance for replacing metal surge rings with surge rope is given in the new sentence “Metal surge rings can be replaced with surge rope of the same or larger diameter to avoid inductive heating or potential ground fault.”
3.11 Wedges
With the use of magnetic wedges in form wound stators becoming more prevalent, information and guidance regarding magnetic wedges was expanded on in this clause. The revised sentence and a new sentence are:
Magnetic wedges should be replaced with equivalent or better magnetic properties magnetic wedges. Caution: Replacing magnetic wedges with nonmagnetic wedges can result in a winding temperature rise of 20°C or more as well as an increase in no-load current, and negatively affect motor performance.
The revised sentence, which added “or better” will be included in the applicable criterion in Item 13 of the revised Accreditation Checklist. Conformance to it will be effective January 2027.
4.2.2 Polarization Index (P.I.) Test
Because the polarization index test often does not apply to random windings the following paragraph addressing this, and providing an alternate test method, was added: This test may not apply to random winding machines since the absorption current becomes negligible in a matter of seconds. A 60/30 second IR ratio test may be performed, with an acceptance ratio of 1.5. (Reference: IEEE Std. 1068, 6.3.1l).
4.2.4 Form-Wound Stator Surge Tests
The following new sentence provides guidance for testing uncured coils so as to help prevent failure due to testing at too high a voltage: Test voltages are reduced for uncured coils and should be agreed upon in advance by the coil manufacturer, service center, and if required, the customer.
4.2.8 Phase Balance Test
The clause text was expanded to provide specific test parameters for the level of voltage to be applied and the time duration. The clause now reads: The phase balance test applies balanced reduced voltage, about 15-20% of rated voltage, 3-phase power to the stator and the current is measured and checked for balance. The test duration should not exceed 5 minutes, and the expected test current should be approximately the rated current.
4.3.3 Armature Windings
Clarified the term “bar-to-bar” by identifying the two types of bar-to-bar test, the high-frequency bar-to-bar test and the low-resistance bar-to-bar test.
4.5.1 Speed
Provided guidance for test running a motor when rated frequency is not available by adding the sentence: When rated frequency is not available, test run at a proportional volts/Hz ratio, without exceeding rated voltage or maximum speed.
Conclusion
The efforts of the Technical Services Committee to revise and improve AR100 are a continual process. Within a year or two, the revision process will become an active agenda item for the TSC. One of the foremost goals with AR100 is to include as many good practices as possible. Further, when it is desired or necessary to add new good practices to the Accreditation Program, AR100 is the conduit. The reason for this approach is that AR100 is the primary source document for the EASA Accreditation Program.
Since AR100 is revised periodically it is a “living document.” Changes to AR100 not only aid with the Accreditation Program, its good practices and other guidance help enable service centers to provide quality repairs that maintain or at times improve rotating electrical apparatus reliability and energy efficiency.
