ANSI NEMA MG 1-2021 PDF

Full title and description

ANSI/NEMA MG 1-2021 — "Motors and Generators". A comprehensive American National Standard published by the National Electrical Manufacturers Association (NEMA) that provides performance, construction, testing, rating and application guidance for AC and DC motors and generators, including practical information on selection, safety, testing procedures and manufacture.

Abstract

MG 1-2021 compiles requirements and recommendations for the design, testing and application of rotating electrical machines. It includes sections on ratings and definitions, electrical and mechanical construction, testing and performance (temperature rise, locked-rotor, insulation testing, number of starts, efficiency), and application data; Part 34 is incorporated in this edition. The edition contains editorial updates and technical revisions to definitions, voltage stress, definite-purpose machines and efficiency tables.

General information

• Status: Superseded (historical edition). Superseded by ANSI NEMA MG 00001:2024 (published by NEMA in 2025).
• Publication date: June 6, 2022 (ANSI approval / publication for the MG 1-2021 edition).
• Publisher: National Electrical Manufacturers Association (NEMA).
• ICS / categories: Electrical engineering — motors and generators (examples: ICS 29.160.20 generators; 29.160.30 electric motors).
• Edition / version: ANSI / NEMA MG 1-2021 (approved as an American National Standard June 6, 2022).
• Number of pages: 648 pages.

Scope

Provides requirements and guidance to assist users in the proper selection, application, testing and manufacture of AC and DC motors and generators used in industrial, commercial and other applications. Covers machine ratings (speed, voltage, current, power), construction types, cooling methods, insulation and voltage stress, performance testing procedures, efficiency classifications and special-purpose/definite-purpose machine requirements. It is intended for designers, manufacturers, test laboratories, specifying engineers and maintenance personnel.

Key topics and requirements

• Definitions and machine classification (including revisions to definitions such as Open Independently Ventilated and additions like Totally Enclosed Nonventilated).
• Ratings and nameplate data: output/input ratings, voltage, frequency, speed, insulation class and service factors.
• Construction and mechanical tolerances (frame, mounting rabbet tolerances and related tables).
• Electrical testing and performance tests: insulation tests, locked-rotor, temperature-rise, efficiency test methods and number-of-starts requirements.
• Application data: effects of voltage variation, duty cycles and service conditions; revised duty-cycle definitions introduced in later editions.
• Definite-purpose and special-purpose machine requirements; updated electrical ratings and manufacturing requirements for hermetic motors (Part 18 revised in this edition).
• Voltage stress and insulation coordination requirements updated in the 2021 revision.
• Efficiency level tables (60 Hz) and references to evolving efficiency classing and alignment steps toward IEC/NEMA harmonization (later editions expanded these topics).

Typical use and users

Used by motor and generator manufacturers for product specification and testing, OEMs for equipment selection, electrical and mechanical design engineers, testing laboratories and quality assurance groups, facilities and maintenance teams for repair/replacement decisions, and regulatory or procurement organizations that reference NEMA/American National Standard requirements.

Related standards

Commonly referenced companion and related documents include later NEMA consolidations and safety guides (for example NEMA MG 00001:2024 which supersedes this edition), NEMA MG 10012 (safety and installation guidance), NEMA MG 3 (sound level prediction), IEC standards for rotating machines (such as IEC 60034 series) and local/regional electrical codes and energy-efficiency regulations. Users often coordinate MG 1 requirements with UL/CSA product standards and national electrical codes.

Keywords

Motors and generators; rotating electrical machines; motor ratings; motor testing; locked-rotor; temperature rise; insulation; definite-purpose machines; efficiency levels; NEMA MG 1; ANSI/NEMA MG 1-2021.

FAQ

Q: What is this standard?

A: ANSI/NEMA MG 1-2021 is the NEMA standard titled "Motors and Generators" that compiles requirements and guidance for the selection, construction, testing and application of AC and DC motors and generators.

Q: What does it cover?

A: It covers machine definitions and classifications, mechanical and electrical construction, nameplate and rating data, performance and type tests (temperature rise, locked-rotor, insulation, number of starts), efficiency tables and application guidance for various service conditions; Part 34 is included in this edition.

Q: Who typically uses it?

A: Motor/generator manufacturers, design engineers, OEMs, test labs, maintenance teams, procurement/specifiers and regulatory bodies referencing machine performance and test requirements.

Q: Is it current or superseded?

A: The MG 1-2021 edition is a historical (superseded) edition: it has been superseded by the consolidated ANSI NEMA MG 00001:2024 (published by NEMA in 2025). Users specifying current requirements should reference the MG 00001:2024 consolidation.

Q: Is it part of a series?

A: Yes — MG 1 is part of the NEMA family of motor and generator publications and sits alongside related NEMA guides and standards (for example NEMA MG 10012, MG 3 and other MG and MG100xx documents). NEMA periodically revises and consolidates MG parts (the 2024 consolidation resulted in MG 00001:2024).

Q: What are the key keywords?

A: Motors and generators, motor testing, temperature rise, locked-rotor, motor efficiency, insulation and voltage stress, definite-purpose machines, NEMA MG 1.