Tom Bishop, PE
EASA Senior Technical Support Specialist

A Summary of Key Revisions to NEMA MG 00001-2024
Although not truly one of the key revisions, this set of standards was formerly designated MG 1 by the National Electrical Manufacturers Association (NEMA) and now is designated MG 00001. NEMA is now following the standards designation methodology of the International Electrotechnical Commission (IEC) by transitioning to 5-digit standards numbering. There are six key changes to MG 00001, and each is detailed below in the sequence in which it is found in the standard.

DOWNLOAD NEMA MG 000001

1. New Design BE and Design CE Motors
The rationale used by NEMA for these changes is that increased locked-rotor current limits were necessary to meet new higher efficiency levels mandated by the US Department of Energy. In the European Union (EU) IEC Design NE (approximately equivalent to BE) and HE (approximately equivalent to CE) motors are already available to accommodate these higher locked-rotor currents. The higher efficiency levels will be termed Super Premium and will align closely with the IEC IE4 levels already used in Europe. These new NEMA design letters are preferred to the existing Design A, which has no limitation on locked-rotor current, because they define an upper limit for locked-rotor current. According to NEMA, this promotes safety by aiding in the proper sizing of equipment in the motor branch circuit.

These changes can be found in the following clauses of the 2024 edition:

Part 1:

• 1.19.1.3 (new)
• 1.19.1.5 (new)

Part 12:

• 12.35.5 (new)
• 12.35.6 (new)
• Tables 12-1E and 12-1F (new)
• 12.38.1
• Table 12-2
• 12.38.2
• Table 12-3
• 12.39.1

2. Class N Insulation
NEMA has added requirements for Class N (200°C) insulation in applicable parts of MG 00001 to close a gap in standardization for motors employing Class N insulation for high ambient applications such as kiln duty and other applications where the end user requires high electric motor reliability in a high temperature ambient.

These changes can be found in the following clauses of the 2024 edition:

Part 1:

• 1.66

Part 12:

• 12.43
• 12.43.2

Part 20:

• 20.8.1

Part 31:

• Table 31.2

3. Design BE and CE Motors Stall Time
NEMA has made an exception for some Design BE and CE motors to the 12-second stall time requirement in clause 12.49 that applies to motors not more than 500hp (375 kW) and rated voltage not exceeding 1 kV. This exception is based upon analysis indicating that 12 seconds may not be achievable for 2-pole motors at the higher locked-rotor current values associated with Design BE and CE motors and that 8 seconds is the more practical limit. To clarify, the limits are:

• 2-pole Design BE — 8 seconds
• Other than 2-pole Design BE — 12 seconds

This change can be found in clause 12.49 of the 2024 edition.

4. Addition of Super Premium Efficiencies for 60 Hz Polyphase Motors Rated 600 V or Less
NEMA and energy advocates agreed upon Super Premium efficiency levels that align closely with the IEC IE4 levels already used in Europe. Due to an expanded scope of motors covered by new US Department of Energy regulations, new minimum and nominal efficiencies for 2-, 4-, 6- and 8-pole polyphase motors have been added to MG 00001.

These changes can be found in Table 12-23 (new) of the 2024 edition.

5. Allowable Voltage and Frequency Variations
NEMA has adopted the IEC allowable voltage and frequency variations to expand on what was already covered on this topic. The intent is to inform end users and electrical utilities as to the performance variation the motor will experience, and how much derating is required in the event of variances in rated voltage and frequency.

These changes can be found in the following clauses of the 2024 edition:

Part 14:

• 14.30.2

Part 20:

• 20.14.1

For general-purpose machines designed to operate at the temperature rise limits of their thermal class, the graph in Figure 1 is indicative guidance to machine users for the required reduction of output power as a function of the combined variation of voltage and frequency that can limit but not necessarily completely avoid a reduction in machine life.

The figure provides the worst case increase in temperature rise and recommended reduction of output power of general-purpose motors as a function of the combined change of voltage and frequency (indicative guideline to users of motors and generators only). 

6. Expansion of Duty or Time Ratings
NEMA expanded the time ratings in Part 10 to include variable load/speed duty, along with the associated nameplate markings and definitions for variable load/speed duty in Part 1. Further, Part 31 was updated to include these nameplate markings for the already-established variable load/speed duties of variable speed motors. The temperature limits for the variable load/speed duties in Part 10 were added to Part 12, and existing temperature limits in Part 31 for variable load/speed duties for variable speed motors were corrected.

These changes can be found in the following clauses of the 2024 edition:

Part 1:

• 1.40.3 (new)

Part 10:

• 10.36
• 10.39.1 c)
• 10.40.1 c), n)
• 10.40.2 c)

Part 12:

• 12.42.1
• 12.42.2
• 12.42.4
• 12.43
• 12.43.2

Part 31:

• 31.3.8.1
• 31.4.1.1
• 31.4.1.2
• Figure 31-2 (title)
• Figure 31-3 (title)
• 31.4.1.6

Note:  NEMA MG 00001-24 is available as a free download at www.nema.org

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Categories: Technical topics, AC motors, Rotors, Stators/windings, Miscellaneous, Standards

Tags: Standards NEMA

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