1.1 ​There is a specific example we are attempting to work through where two different EASA shops ran tests on the same motor (results attached). There is a conflict of MG 1-14.35 interpretation where the relative current unbalance was approved but is being argued by the customer. I am reaching out to better understand this standard to try to get this argument solved.

1.2 ​I would like to ask a question about NEMA design letter A and B for motors. Could you please help me to understand the application differences between these two designs? For what type of applications do we use Design A motors and B motors?

1.3 ​Do you have a standard that covers the motor to pump interface for 4-inch submersible motors. I can't seem to find the standard on your website, but many manufacturers refer to being in conformity with NEMA 4-inch.

1.4 ​Does NEMA MG 1-2016 and NEMA ICS 7.2-2015 suggest or require that shaft grounding be provided for motors controlled by a VFD? I am being told by a customer it is a code violation if shaft grounding is not provided and all of my equipment suppliers say it is a recommendation and not a mandate.Can you please clarify?

1.5 As per a project specs, motors shall be NEMA Design B, motors came with no indication of NEMA Design B either on the nameplate or the data sheet. When asked for confirmation, it was stated that motors are IE3/NEMA premium.Do motors being IE3/NEMA Premium necessarily indicate that motors were built to NEMA Design B?

1.6 ​I have a technical question regarding the correct interpretation of NEMA MG 1, Section 14.4.2, where it addresses motors having a service factor 1.15 or greater and can operate at altitudes higher than 1000 m “at unity service factor”. Is this saying that they can operate with service factor of 1.0 or only the service factor stated on the nameplate?

1.7 ​I have to replace an old GE A-C Motor, Dual Voltage Repulsion-Induction. The plate on the motor declares it a Type SCR, Frame 65A, 1/2 HP, Phase 3, Cy 60, RPM 1760, Volts 110, Amps 6.4, Volts 220, Amps 5.2. I cannot find any motors with a 65A frame, and I don't believe that they had SCR motors this old (approximately 1949). So did NEMA change the standards? If so, what would SCR have stood for in 1949? What would a modern equivalent to a 65A frame motor be today? How do I find out?

1.8 ​Kindly would like to ask you, without obligation, if you could let us have any Information about protection of three-phase motors within the NEMA Standard (class 1, Division 1). We should know whether only 1 current rate (the so-called service factor) will be valid over the complete voltage range from -10 % to + 10 %. Will necessary information be found in NEMA MG1-2016 and/or NEMA 12-12? If so, will we have to buy this document

1.9 ​I have a NEMA motor used to circulate water on the high school swimming pool and I was wondering what type of greese and how often should I greese the motor it runs continuously?

1.10 ​I am looking for a NEMA Ratings and IP Equivalency Chart. I have a motor with an IP rating of a 44. However, I was told by the manufacture that they do not make a NEMA reference on the nameplates for small motors. Would you be able to provide me with a NEMA Ratings and IP Equivalency Chart?

1.11 ​I want to design explosion proof electrical machine. Please give information about the standard, i will order the standards

1.12 According to 7.8.5.2, if unfiltered vibration level exceeds the limit of table 7-1 , and if the 2 time frequency component exceeds 90% of the unfiltered limit in table 7-1, then the procedure in 7.8.5.3 may be used . If the effective vibration does not exceeds 80% of the value in table 7, the motor is acceptable ( per 7.8.5.3).Our motor shop asked me to explain how to get the unfiltered vibration monitored per 7.8.5.3. and what is “ a complete slip cycle”. I could not answer.

1.13 ​How might a soft start impact the number of starts and rest time for 1200 HP motors?

1.14 ​NEMA MG 1 Table 8 has values up to 250 HP motors. Can the table be extrapolated to large motors such as 1200 HP? If not, are there A, B and C values that can be used to determine the allowable number of starts and rest time?

1.15 Does NEMA MG 1 cover ECM's?​

1.16 ​I am a rod pump analysist and we are trying to set guidlines for our variable frequency drive units. All of these units have NEMA D motors and I'm trying to find the safe minimum and maximum hertz speed for these motors. Our motors are generally anywhere from 30-75 hp.

1.17 I am looking to run 2 motors at the maximum RPM the can safely be run at. The serial numbers of the motors are EV9105006001 and GW9117104001. I was wondering what is the maximum RPM the motors can run at, and what will be the side effects of running the motors at this speed continuously? The reasoning behind this is we are looking to get some rotaflex units to operate at higher speeds on the straight portion, so that when the corner speed is decreased to a safe operating speed we will still be able to reach our target strokes per minute. ​

1.18 ​In regards to NEMA MG 1 10.37.2 Standard for Locked Rotor kVA per horsepower do you have a rough estimate of what HP size motors fall into each NEMA Code Letter category? Example Code Letter H = 7.5 to 10 HP

1.19 I am in the process of ordering a new 3-phase 480volt 7.5hp motor for our ferry terminal (hoist application). I have requested the motor to be a NEMA design C, however the sales rep has told me that they no longer can make Design C because of new regulations. They recommended I upsize to a larger horsepower Design A motor however I am reluctant to do that since the hoist system was designed for 7.5hp. Is there anything else I can do to ensure this new motor will be able to handle the high initial torque of our hoist system?​

1.20 Would a submersible motor (for sewer) be more heavy duty (better quality, longer service life) if it complies with NEMA MG 1, Part 31 vs one that does not not?​

1.21 ​Is NEMA MG1, Part 31 applicable for dry installed motors only, and not submersible motors?

1.22 ​I am assisting with a large hydraulic forging press application. There has been some disagreement amongst the engineers involved in the project regarding how often the (15) 1200 HP, 4160V motors can be shut on/off per hour. Some of us are in the camp that these motors should not be shut off during production (1 minute of pressing time and 8 minutes of idle time), however we haven’t found a reference we can point to that spells out a motor of our size explicitly. We have referenced NEMA MG 10 as a source however we are looking for anything additional as to whether the on/off function is possible. Do you have such a source or could you offer your opinion on the applicability of using a soft start drive to turn off these motors during the idle portion of the cycle?

1.23 ​Working on building and qualifying a 400Hz AC Motor. The customer drawing is specifying testing IAW MG 1 spec. MG 1 spec that we have, 2010, only makes reference to 50/60Hz machines. Do you cover the testing of 400Hz machine in any of the later or earlier revisions/editions?

1.24 ​I am looking for standard for slip ring motor. But cannot find it in MG-1. So I am wondering I should look at which standard?

1.25 I am searching for either a NEMA or IEEE standard for performing airborne sound level measurement of large motors (> 150 hp). Measurements are typically performed three feet from the machine either at no load or at rated load. ​

1.26 I have some motors on some equipment which is from japan and the EX P. Degree is d2G4 is this equivalent to the USA STD of Class 1 Group C, D Division 1​

1.27 Looking at an electric motor NEMA rating is a NEMA L can you tell me what L means?

1.28 We manufacture electric motors in Guadalajara Mexico. so, I would like to know if exist the possibility to manufacture the conduit box housing in material poliamida reinforced with fiber Glass (30 %). (Nylon reinforced).The question is because, due the news developments material in resins reinforced have equivalents mechanical properties like the steel.Your reference 4.19.1 of the NEMA std manual

1.29 At some point of time in the past NEMA changed the values of Locked Rotor Code (kVA) of the motors. I am told Code " F" is really equal to new "E". At what time in the past year was this change was made? And is there a table available where I can compare the codes (old Vs New). I am currently looking at a plant which contain some old induction motors stamped with the older letter code. I need to calculate the inrush current but I am told Code letters are not the same we see in literature today. This induction motor was manufactured back in 90's.

1.30 I would like to clarify locked rotor current between NEMA MG.1 para code letter 10.37.2 and NEMA 12.35.1 design code. 1. which is order to priority to apply LRC in both code ?2. Can we using this motor, if when actual test LRC is more higher than NEMA 12.35.1 design code even though motor was designed by NEMA MG.1 para 10.37.22 code letter G.3. Could you kindly provide the reference or relevant doc about these issue.

1.31 Sir, I would like to know the minimum resistance and reactance value of a motor and useful calculation formulas.

1.32 What does motor type 56 FR mean? Could you send me some information on this by email?

1.33 Does NEMA have a modified Design Letter Standards for Premium efficiency Motors? If so, could you please share where I can find documentation on the theory?Please note – one of the books I used in my Graduate Studies “Electric Machines by Dino Zorbas” – page 231-- fig 3-17 (pic attached), illustrates the speed torque characteristics of the NEMA Design Letters A, B, C, & D Motors. I observed the speed of Design A motor drops between 10 – 20 % at starting of the synchronous speed; therefore, it draws very high current for that duration. Our Design Criteria constraints us to Design “B” motors. Question One of our Design Vendors used the term “Modified Design A” to describe a NEMA Design Letter for a Premium Efficiency motor. Some of the research I did indicates the cooling fans design was modified from standard motor construction, this modification is considered premium efficiency since the new fan design allows more cooling. Was the Speed/Torque characteristics modified in the premium efficiency motors?

1.34 Could you please help me understand the differences between the Traditional NEMA Design Letters A, B, C, & D, and the Modified NEMA design letters with respect to torque speed characteristics. Note that our Design Criteria requires Design B motors; however, I was told the modified A has the same characteristics.

1.35 Can you inform that which code is provide the fulfill information regarding the recommended practice for requirement of Resistance temperature detector(RTD’S) in AC generators.

1.36 What is the difference between these two standards in general terms? Can a motor be both MG1 and MG2? If they are different, is there a document that compares the two?

1.37 The NEMA MG1 standard states a “shaft parallel to foot plan” of 0.015”, but that incongruent since parallel requires an angle not an offset. Could you provide some guidance on how the parallel tolerance is measured?

1.38 I have come across an issue with the BA dimension (C-Flange face to the center of the front foot mounting hole) being different between motor manufactures. The Company A catalog has a BA dimension for a 182-4TC frame motor to be 3.50". Company B motors have some that are 3.50" and some that are 2.75". Can you advise if NEMA standards control this value? Also can you advise the NEMA standard that covers this issue? Thank you for your time and I look forward to your response.

1.39 1. We are designers and manufacturers of agitation equipment which use electric motors. We are experiencing no load amperage on fractional horsepower motors that is higher than the full load amps on the NEMA nameplate provided by the manufacturer. When we questioned the manufacturer on this, we were told "It is normal for small motors to have relatively high no-load current, especially if the line voltage is above nominal." Is this correct? 2. It seems to us that some motor manufacturers are gaming the NEMA standards when it comes to the horsepower and service factor specification. We are finding examples of motors spec'd as 3/4 HP with a 1.8 SF. Of course they are running at 1HP or greater, but take advantage of the ignorance of the buying public to extrapolate that fact. Would NEMA have anything to say about that or is it perfectly legit?

1.40 The question is in regards to Table 32-3 and the 5 degree C delta when comparing Rise-by-Resistance to Embedded Detector temperature rise. This maximum delta requirement seems to be a recent addition as it was not present in the 1993 version of MG-1. In discussion with generator manufacturers, I am told that this delta maximum is not achievable unless the embedded detectors are located in stator winding spots that are not hot spots. As a customer of generators, we would prefer that embedded detectors were in the hot spots. In hot spots, the delta rise tends to be 25-30 degrees C.

1.41 Concerning "NEMA Standards Publication MG 1-2006 Revision 1", part 12.54.1. One of the given conditions is "Two starts in succession (coasting to rest between starts) with the motor initially at the ambient temperature or one start with the motor initially at a temperature not exceeding its rated load operating temperature.” I have been told that this means 2 cold (or 1 hot) starts "per hour," but I don't see the "per hour" in the specification. How should I interpret this?

1.42 Are there any guidelines related to motor power factor? I have a 200Hp, 460VAC, TEFC motor that was recently installed that has a 95% power factor, which meets the NEMA guidelines for energy efficiency. However, the power factor is .81. This seems really low compared to some other motors I've researched. I would expect it to be in the .85 to .88 range. This low power factor will cause the motor to draw more current. Although this does not increase my KW, it does increase my KVA, which will require the utility to provide more power. I thought the reason the energy efficiency guidelines’ were to reduce overall power consumption. Shouldn't the motor power factor be a consideration or am I missing something?

1.43 We have recently noticed an apparent change in the NEMA specified hi-potential test voltages.The specific section in question is NEMA MG 1-2006, Part 12, Page 2, Paragraph B.2.A that specifies a test voltage of 1500V for motors rated 1/2horsepower and less and 250V or less.Previous versions of NEMA MG 1 specified a test voltage for these motors of 1000V. This results in a 50% increase in the test voltage. We are concerned that the increased test voltage may be overstressing the motor insulation, as our motors are typically hi-potential tested at least three times (the motor manufacturer, and our customers).Please confirm if the 1500V test voltage is indeed the current specified hi-potential test voltage for these motors. If it is correct, we would appreciate your comments regarding the reason for this change.

1.44 We have a little (big) problem concerning the dimensions of a type C flange (the motor frame is 182 TC). On page 59 of NEMA standards publication, it is not clear which plane the dimension AH is referred to (I suppose that AN means AH, in the upper drawing). Could you be so kind to send me a drawing with the real dimensions for a motor frame 182 TC?

1.45 We are seeing a reference to NEMA MG 1-22-61 in ac generator specifications. I am not sure what or where this reference comes from. I am looking in my copy of MG 1-2003, rev 1-2004 and do not find a 22-61.

1.46 We are a producer of turbo generators. On a new project (32MW generator for 50Hz and 60Hz market), the customer requires NEMA approval certification. How can that be achieved? Is it via a notified body? Is it just by following design guidelines according to NEMA? Or any other way? Please advise, and respectively assign a contact for further clarification!

1.47 I am currently conducting HIPOT testing on an electric vehicle motor. I was writing to request some clarification based on the HIPOT sections of the NEMA MG 1 standards. The specific motor that I am testing has three ac phase cables connected to the windings. While reading through MG 1-3.01.7 and 3.01.8, I am a little confused if I should be including these in the NEMA HIPOT test, or if these cables count as an accessory or component that should be tested separately.

1.48 Is there a chart made that shows runout tolerances set by speed? We are in need of a guideline for acceptance criteria. Any help would be much appreciated.

1.49 I am looking for a NEMA standard that describes the criterion for material selection for low voltage motor frames. We have to decide whether to go for a motor with steel frame or a cast iron frame. Motors are 315 KW.

1.50 I got a request for a NEMA 320TSC adapter. What is the meaning of each letter (TSC) on the description?

1.51 When going over the 2010 revision of NEMA MG 1, I noticed a section that does not make much sense when being read. Section 7.8.5.2 Filtered VibrationThe second paragraph states that if the level does NOT exceed 90% of the unfiltered limit then the machine has failed and corrective action is required.The third paragraph states what to do if it DOES exceed 90%. In regard to the second paragraph if you have vibration under a set value, you should find that acceptable rather than failing the machine.

1.52 Recently we had a 350 Hp electric motor 440V/3Ph/60 Hz burned in 3 phases. Motor has only 22,000 hours operating directly connected to a centrifugal compressor. Company hired to do the repair job says that the source of the problem is that this motor has no code to operate with a solid-state starter. We asked the motor manufacturer and they answered that there is no such a thing, but repair shop insist in their diagnosis and said that it is in the NEMA MG 1 standard. We can’t find where in this standard is such requirement.

1.53 Can you confirm that the NEMA Table 12-14 efficiency values match the values for IE3 50Hz exactly (for the equivalent rating)? I may have outdated information, but there were a few ratings that did not match—88.4% vs 88.6%, etc.

1.54 I have a question about the Locked-Rotor Torque, Breakdown Torque, and the Pull-Up Torque Tables found in Part 12, page 10 of the 1998 rev. 2 MG-1 standards. My question is Are these tables the same tables that where used in 1976?

1.55 I have attached a tech sheet for some submersible pumps that appear to meet the NEMA Premium™ Efficiency standards. As you can see, these motor Hp’s don’t line up exactly with the NEMA min eff charts, so how do you determine if this will qualify for the NEMA rating? Does the Hp get rounded up or down to the next tier? Or is there another Premium Efficiency Chart that has more increments?

1.56 I'm wondering the difference between a 256TY NEMA frame and a 256TC NEMA frame.

1.57 The temperature rise limits in 12.43 are based on a maximum ambient of 40 degrees C, as stated in the clause. Both 12.43 and Table 12-8 are based on winding rise by resistance. The highest temperature rise values in 12.43 are 70 degrees C for Class A, 90 degrees C for Class B, 115 degrees C for Class F, and 130 degrees C for Class H. Adding ambient to highest rise results in maximum temperature limits of 110 C, 130 C, 155 C, and 170 C for Classes A, B, F and H, respectively. As I interpret it, a motor complying with the limits in Table 12-8 of 12.56.1.1 would be in excess of the limits of 12.43 by at least 30 degrees C for Class A, 35 degrees C for Class B, 35 degrees C for Class F, and 45 degrees C for Class H. Both clauses apply to medium motors, thus my perception is that the motor configurations are, or could be, the same.What am I missing?

1.58 1) I am working for Quebec government that takes care of health and safety for workers. We would like to know if there is any requirement (standard) concerning the maximum ventilation openings dimensions on a TEFC motor? Depending on holes dimensions, the fan could be accessible by a worker finger. 2) In MG 1, Table 12-8, the temperature values for a medium motor far exceed the values that would be obtained by applying clause 12.43. This appears to be a discrepancy. Please explain via email how to interpret Table 12-8 and clause 1.43 such that they are consistent with each other.

1.59 We are having a difference of opinion on the interpretation of the NEMA motor standard regarding permissible runout on the shafts of JM frame motors. Can NEMA clarify to resolve the dispute? We interpret the max runout to be .002 for shafts for 143JM - 256JM, .003 for 284JM - 326JM frames, (per Section II, Part 18, Page 86). My motor supplier is saying that because JM shafts are an extended length, there is a caveat in the standard that allows max runout of .004 T.I.R. We can only find that this applies to extended length shafts on C-face motors in the standard.

1.60 In your MG 1 documentation, section 12.38.1, Table 12-2 (Locked Rotor Torque for Design A & B), why doesn't the table show any information below 1/2 Hp and what does the value '...' in the table mean?

1.61 Is there a maximum number of electrical motor starts (up to full speed) within an hour that is not recommended by NEMA to exceed? It is my understanding that the intent of a maximum number is to avoid damage to the motor due to excessive heat from the start load. Motor specifications include 150 Hp, 900 rpm

1.62 We have a question on Design C motors to consult with you. We understand that a Design C motor must meet the requirements of NEMA MG 1, at least conform to this standard on locked-rotor torque, pull-up torque, breakdown torque, locked-rotor current, slip, and etc. Do these requirements have an allowance (tolerance)? As you know, the Design C motor is designed as per NEMA MG 1, the average performance specification can meet or exceed NEMA requirement, but a small part of these motors may have a deviation, for example, some 25 Hp, 4-pole motors have a locked-rotor torque, 198 percent of full-load torque, but NEMA requires 200 percent. Are these 25 Hp, 4-pole motors with deviation belong to Design C motor? For another example, NEMA MG 1 requires 10 Hp Design C motors have a locked-rotor current not exceeding 162A at 230V 60 Hz, but some motors with deviation has an 8 percent higher than the standard current 162A. Can these motors be regarded as Design C motors? Do these Design C motors have to be re-designed to assure each motor meets all the NEMA requirements without any percent allowance? 2. You mention "resistance" test method when determining the insulation life of a motor. Where can I get information on the resistance method? 3. Does this standard include the small motor dimension standard for NEMA 8, 11, 14, 17, 23, and 34? Those are the primary sizes for this gear reducer family that I am working on. I looked in the MG 1 condensed version and it has the type of information I am looking for, but the smallest I found was the NEMA 42.

1.63 The explanation for sealed windings is very clear. We would also like to ask if there is a standard and definite definition of “sealed motor” in the motor industry according to NEMA the standard.

1.64 We would like to ask if there is a standard and definite definition of “sealed motor” in the motor industry. According to the NEMA standards publication, there is a classification of motor by “machine with encapsulated or sealed windings”. Can we say that such a motor is an electrically-sealed motor?

1.65 Attached is the 1998 NEMA Table 12-11 and on it we have highlighted two motors and hand written in what the efficiency value was from the factory testing. The value recorded when factory-tested is higher than the minimum efficiency value, but lower than the nominal value. The customer is contending that the factory efficiency testing must meet or exceed the nominal value in order to meet the NEMA standard. The article below leads me to believe otherwise and that the efficiency only needs to be at or above the minimum efficiency value. What is your or NEMA’s take on this?

1.66 Would table 12-11 still apply to a custom built motor that is operated at 50Hz but on 460V?

1.67 Our client is insisting that NEMA MG 1-1998 efficiency requirements in Table 12.11 apply to 50 Hz motors. Would it be possible to get a letter from NEMA stating that NEMA MG 1-1998 Table 12.11 only applies to 60Hz motors and does not apply to 50 Hz motors?

1.68 Section MG 1-20.45 did not point to the table in MG 1-20.42. We recovered the 1964 version and it does provide those values that we are looking for. We did have one question. The 1974 version removed some values from this table as compared to the 1964 version, specifically the values for 250 Hp–500 Hp for rpm at a range of 1800–3600. Additionally, the note “This formula may not be applicable to the ratings not included in the above table. Consult the manufacturer for the ratings which are not shown.”

1.69 I am trying to verify the NEMA MG 1 requirements in-place at the time of motor purchase. Our motors were purchased in the 1967 to 1972 timeframe. Specifically, I am trying to determine when exactly Section MG 1-20.42 “Load for WK2” and revision to Section MG 1-20.45 “Subpart A and B” for motor became in effect. I have found a copy of the 1964 and 1974 version. The 1964 version does not provide Section MG 1-20.42; it is provided in the 1974 version. I was hoping you could provide any historical information on this section and when the Section MG 1-20.42 and Section MG 1-20.45 “Subpart A and B” revision came into the MG 1 standard?

1.70 Can you please elaborate on NEMA MG 1-2011 Section 12.68? I don't understand how the dc voltage is up to 110% of rated voltage while the ac voltage to the rectifier should be rated for plus or minus 10%.

1.71 Our company supplies and installs diesel generator sets in the range of 2.5-2,000 kVA. We have a request to supply a diesel generator set for a public tender in Greece. The tender states that the generator of the diesel generator set should comply with standard NEMA MG 1 Part 22, among other standards (IEC, CSA etc.). I can't find any references to MG 1-22 in the free, condensed version, nor is it in the contents table of MG 1-2011. After some internet research, I have found a citation stating that MG 1-22 referred to synchronous generators. As far as I understand, it was part of previous editions of NEMA MG 1 and at some point it has been repealed and replaced by NEMA MG 1 Part 32 and ANSI standards C50.12, C50.13, and C50.14. Did I understand this correctly?

1.72 If a motor complies with NEMA MG 1, Part 31.4.4.2, does that mean it is compatible with 'V/f' type variable frequency drives only, or “vector” type variable frequency drives only, or both?

1.73 I need to know what parts of the motor and generator standard regulate the horsepower rating of electric motors. I am trying to explain in a civil manner to some members on a forum that the horsepower ratings of electric motors from the motor manufacturer itself are NOT inflated values as that could get them in hot water big time with you guys. I try to explain to them that companies that buy the electric motors are allowed to inflate the value, NOT the manufacturer of the motor. Unfortunately, the only way to make reason with them is to show direct proof from you guys what guidelines electric motor manufacturers most follow when rating horsepower of their motors.

1.74 I need to know the difference between a 254TC frame and 256TC NEMA frame. Also, if I could get a catalogue or brochure pertaining to NEMA ratings I would greatly appreciate it.

1.75 I have the MG 1 standard and my customer wants a 0.4 Hp Design B type motor, but it runs at 400 Hz. Everything I see in NEMA MG 1 is for 50/60 Hz. Please advise if there is another specification I am missing.

1.76 We have to clarify a customer complaint and desperately need the tolerance classes for a NEMA flange 9”. Is it possible to get just a short overview?

1.77 I was reading through NEMA MG 10 and noticed an error on Table 7. Under 2-Pole, column C, at 100 Hp, the table says the minimum off time between starts is 110 seconds. This should probably be 220 seconds. 110 seconds is for a 4-pole motor.

1.78 I refer to three-phase squirrel cage asynchronous motors. Until now, we ordered LV motors rated up to 200 kW. Bigger motors were ordered for HV. I would like to know if this limit for LV motors is according to NEMA MG 1 standard or is it possible to order LV motors until 375 kW (Energy Premium Motors)?

1.79 One of our vendors sells a NEMA 3.5 Hp motor. Can a NEMA motor be made that doesn't have a standard Hp size?

1.80 Regarding polyphase AC motors, is there a standard or guideline for current balance between the 3 phases?

1.81 What are NEMA's standard generator sizes? I am looking for sizes 1000 kW and larger.

1.82 I have general questions about NEMA motor nameplates.The NEC 2011 Chapter 430.32 is writing about a "temperature rise of 40°C" in case of overload protection. A continuous-duty motor with a marked service factor of 1.15 or greater or with a marked temperature rise of 40°C or less can carry a 25% overload for an extended periodwithout damage to the motor.What is the meaning of "temperature rise"? Where I can find it on the NEMA motor nameplate? Is this maybe the AMB?What is the difference of "FL AMPS" and "SF AMPS" I found on a motor nameplate? I think SF_Amps = SF * FL_Amps

1.83 I do find it a bit hard to understand how progressive run out is acceptable to NEMA. But of course, I didn’t write the spec. You mention longer shafts have more runout tolerance. Can you advise what the allowable runout would be on longer shafts, say 10” long or the longest noted?

1.84 I have several new vertical solid shaft motors that have progressive run out from the motor base to the end of the shaft, starting at .0005" at the base and increasing to .002" at the end of the motor shaft. This will continue to increase the farther I get from the motor and as such, my rigid coupling will have excessive runout which will not be acceptable to the sealing device mounted on the pump. (The Pump AWWA Std for lineshafts is .005" per foot, which is much tighter than what the motors have been machined to.) The manufacturer is refusing to help me as they say the runout of .002" is within NEMA tolerances. I can live with .002" of runout if it is parallel to the centerline of the motor, not progressive. I am looking for clarification on the specification and whether NEMA addresses progressive runout, as it is generally not an acceptable machining practice.

1.85 I have a big debate with contractor on pump motor, which is specified in our specs (NEMA MG 1 design B), while the contractor is proposing an IEC standard and insisting that it is the same as NEMA MG 1. Please advise me the difference between where the deviation occurs.

1.86 I have a question regarding the motor frame dimensions given in Part 4 of the NEMA MG 1 standard. There are several dimensions that are defined graphically (Figures 4-1 and 4-2 of Part 4), however no quantitative information is supplied for the dimensions. For example, Dimension O ‘Top of horizontal machine to bottom of feet’; Dimension P ‘Maximum width of machine excluding terminal housing’; and Dimension AB ‘Centerline of shaft to outside of terminal housing’. It appears that these dimensions are manufacturer-specific, however, there are documents labeled “NEMA” floating around the internet that supply values for the O, P, and AB motor dimensions, usually with the footnote that the dimensions may vary by manufacturer. Does NEMA impose any specific limits on the O, P, and AB motor dimensions for compliance with a given NEMA frame designation? Or are there industry best-practice standards that influence or control these dimensions?

1.87 In reading both the 2003 and 2006 versions, Section 12.41 "Breakdown Torque of Polyphase Wound-Rotor Medium Motors with Continuous Ratings" has an error in the table. The table shows the synchronous speed of the 50 Hz machine as 100 RPM and it should be 1000 RPM.

1.88 I have a general question concerning the service factor for standard and non-standard NEMA motors. Is it true that NEMA MG 1 prescribes a service factor of 1.15 for every motor or is this up to the manufacturer?

1.89 I cannot locate what the difference is between motor frame C56C and 56C. There is no evidence of C56C frame; however, it is used as the NEMA frame number. Can you help?

1.90 This question is in regard to the nameplate on single phase electric motors. Salesman 1 tells me that a voltage rating of 230V means that the motor will operate between a range of 207V to 253V (+ or - 10%). Salesman 2 tells me that a voltage rating of 208V-230V means that the motor will operate between the voltages of 187V to 253V (208 less 10% and 230 + 10%). Salesman 3 tells me that a voltage rating of 208V-230V means the same thing as 230V and will operate safely between 207V and 230V, and there is no (affordable) motor that will operate between 187V and 253V. What does NEMA say? Why the confusion?We have a situation where we need to make the best choice on motors for mobile equipment on our farm where we can plug the equipment into a building with a 208V service one day and move the same equipment to a building with a 230V service.I am looking for full-load efficiencies of "premium efficiency" 480V, 8-pole motors, but noted that Table 12-12 in NEMA MG 1-2006 Revision does not include them. Is this full table available? In accordance with subclause 31.4.4.2 (Voltage Spikes) from Nema MG1, stator winding insulation systems of definite purpose inverter fed motors shall be designed to withstand the following limits at the motor terminals1. For motors with Vrated £ 600 V, Vpeak should be less than or equal to 3.1*Vrated (where 3.1 = 1.1 * 2 * sqrt(2) ).2. For motors with Vrated > 600 V, Vpeak should be less than or equal to 2.04*Vrated (where 2.04 = 2.5 * sqrt(2) / sqrt(3) ). We were wondering why this difference exists. Why is there not a single criterion that is valid for every base rating voltage? Now looking a little more deeply into the equations of the two criteria, one can notice that the criterion valid for motors with Vrated £ 600 V does not take into account the term sqrt(3). Does it mean that this criterion is valid for delta-connected motors only? That is, if the motor is star-connected, should the criterion 1 be divided by sqrt(3) to be correctly considered? On the other hand, the criterion valid for motors with Vrated > 600 V takes into account the term sqrt(3) and this may lead to the conclusion that it is valid for star-connected motors only. Is this the case? Or can the criterion 2 be literally applied to delta-connected motors too? In other words, does the term Vpeak of these criteria refer to phase voltage (line-to-neutral voltage) or line voltage (line-to-line voltage)?

1.91 What if the motor I am referring to is reduced voltage, soft-start with no VFD?

1.92 1) Is there a standard for motor manufacturer to follow in regards to shaft voltage/current?2) What are the upper/lower limits for shaft of voltage/current? >3) I have read where 4160V motors "typically" include one insulated bearing in the motor to protect against shaft voltage/current.

1.93 I am a vibration analyst working in Michigan. I have a client that wants to know what a good vibration level is. I am quoting your MG 1 mechanical vibration standard. I would like to know if the values given in the table are "filter-in" or "filter-out". I do not have the whole standard, just the page with the table that was faxed to me by a motor repair shop.

1.94 Are the following (ODP, TEFC, TENV, TEAO) motor codes or motor designations?

1.95 I am a specifying engineer and would like to improve our specifications with regards to inverter duty-rated motors. I see NEMA has a standard, MG Part 31, that explains how to build a NEMA-rated motor. We can specify that the motors need to meet this standard, but what about proof? Does this standard also require that the motor come with a nameplate that states it was constructed to meet this standard? We have some suppliers that are giving us a verbal confirmation that their motors are inverter duty-rated, but this does not fly in our business. Perhaps you have a written standard specification to obtain an inverter duty-rated motor?

1.96 The user would like clarification on whether or not compliance of a motor to Part 31 would/could also cover or partially cover its compliance to Part 30 of the MG-1.

1.97 A. Customer has a group of pumps driven by 50Hp, 1800 RPM, open drip-proof, premium efficiency motors. One of the pumps on the order was factory-certified tested with a calibrated drive motor. The test verified the pump performance in that the maximum load that the pump could produce at any point in its operation parameters was 48.9 BHP. B. The motors are operating on a PWM variable speed assembly with by-pass contactor that enables them to operate on commercial power in the event of the VFD failure. C. When the pumps are operated at design conditions which are 48 BHP, the current on the motors either on PWM system or on the commercial power by-pass system is approximately 10% over the nameplate full load amperage. D. The input power is balanced within 2 volts and is 498 - 500 - 498. We have operated the motors on the VFD at 460, 470, 480, 490, and 500 volts without any appreciable change in motor full load amperage. E. The motors are rated 94.5% efficiency, 57 full load amps. Unfortunately, it would appear that they are operating at a lower efficiency, and at 62, 63, and 65 amps. The motor manufacturer indicates that the published data in his design information is a "nominal" rating and that the motors on this particular order may vary a significant amount from the published data. F. The overcurrent problem is identical on all of the pumps and motors on this particular order, so it just isn't that one motor may be an anomaly. Our questions are as follows 1. What is the definition of "nominal" efficiencies? 2. Is there a range of efficiency values for this motor Hp/Speed that the production motors must meet in order to comply with NEMA standards? 3. Is there a "minimum" efficiency that these motors "must" meet to comply with these standards? 4. Does NEMA actually require that individual manufacturers test their motors to comply with NEMA standards, and does NEMA actually review or witness these tests to ensure compliance? 5. Does NEMA visit motor manufacturers and randomly test a motor now and then to ensure that the motors that are being produced meet NEMA specifications?

1.98 Was there an efficiency rating for NEMA D motors installed during the 1970-1980?

1.99 Can NEMA Nominal efficiency levels be met at either full load or 3/4 load, or just at full load? I have been involved in previous programs that accepted either.

1.100 The efficiency levels are provided with nominal and minimum efficiency values. I am correct when I say that a motor rating must meet both of these criteria and not just one or the other, right?

1.101 I am seeking the standard for the permutations of the three phases in an L21-20 plug or receptacle. There are two possible permutations of the three phases, and using the wrong one causes motors to run in reverse, which would be detrimental. I am familiar with a labeling of the 4-poles as W for system ground, and X,Y,Z as the three phases of 120V with respect to W. Is the standard to have X leading Y, Y leading Z (each by a third of a cycle) or to have X leading Z, Z leading Y (each by a third of a cycle)?

1.102 How are current pulsations defined in NEMA MG 1 (in regard to an induction motor driving a reciprocating compressor)?

1.103 What under voltage is allowed on 380/220-volt systems at 50 Hz? How low can it be set at for a transfer switch with a default setting at -15% dip?

1.104 Our company is a motor manufacturer in Korea. The standard of our motor is NEMA. There is a technical data sheet (MG 1-1993, Part 12, page 21, section 2) about tests and performance of ac motors. In this table, NEMA suggests the data to keep the value of efficiency. I wonder that when our company makes a pole change motor, the value of efficiency is really difficult to follow the NEMA standard in case of high efficiency motor. The data is only for a one-pole motor, not for a pole change motor. I need a document that this table is the standard of one-pole motor and pole change motor is not adapted as our customer wants an official document from NEMA.