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How to Read a NEMA Standard


In order to successfully use NEMA standard publications, it is important for the user to understand what NEMA standards are and what types of information they contain. This brief introduction is further explained in the NEMA publication, Standardization Policies and Procedures.

Determining if you’ve found the standard (or other technical document) you need

NEMA publishes five basic types of technical documents, each with slightly different audiences in mind:

  • Specifiers
  • Installers
  • Contractors
  • Inspectors
  • MRO (Maintenance/Repair/Operations)
  • Engineers and Designers

Types of NEMA publications:

  • Standards
    • May contain information relevant for all audiences; consult the scope and document description.
      • Certain standards are available at no charge on the NEMA website.
      • Tables of contents and scopes of recent standards are on the website so readers can tell if what they are looking for is included in a certain standard.
  • Application guides
    • Guidelines are geared toward the layperson, installers, inspectors, and employees working with the given product.
      • There are many guides available at no charge on the website.
  • Authorized engineering information
  • Suggested standard for future design
    • For engineers and industrial designers, these standards suggest a sound engineering approach to future development.
  • White papers
    • Intended for a broad audience, including the layperson, installers, inspectors, and maintenance personnel. They contain practical tips on subjects like phantom voltages, the hazards of working with electrical equipment hot, and dealing with water-damaged electrical equipment.

Tips for selecting the proper document(s)

  • The reader needs to be clear on what he/she is looking for in the document.
    • For example, the “test requirements for corrosion protection of panelboards.”
  • The first thing a reader should do when looking at a standard is to read the scope to determine if the document covers the area of interest.
    • For example, the scope of NEMA PB 1 would lead the reader to suspect that the above test requirements might be found in PB 1; the scope of PB 1.1, on the other hand, would suggest not.
  • If the scope of the document in hand does not cover the material the reader is interested in, the reader should go to the section on Referenced Standards. The information there may lead the reader to a standard that does cover the information he/she is interested in.
  • Once the reader knows they are on the right track, they should go to the table of contents to find the appropriate section of the standard that is likely to contain the information they seek.
  • For example, NEMA PB 1 is intended to provide information primarily to manufacturers of panelboards. It will cover some to all of the requirements a manufacturer's product needs to meet or exceed. Other requirements will be contained in other standards such as UL 67. So a manufacturer would want to look at PB 1 from this perspective—“It has some of the requirements I need to know, but I need to go elsewhere to find the rest of the requirements.”
  • An installer or maintenance personnel would read this information differently. Perhaps he or she would skim “Markings” and “Construction” but should be directed towards PB 1.1, which addresses installation, operation, and maintenance directly.

Contents of NEMA standards publications

A NEMA standards publication contains a combination of the following items, except that a NEMA adoptive standard shall comply with the rules and procedures of the standards organization responsible for its development.

  • Scope. A clear, concise, and comprehensive statement of the coverage of the standards publication shall always be included.
  • Definitions. If items used in the standards publication require definition, the definitions shall be included as a separate part of the publication.
  • General. General standards, when used, are those having broad appli­cations to the products covered by the standards publication and not otherwise classified.
  • Rating. Rating standards, when used, include specific ratings of—or methods of rating—the equipment in such units or measurements as are appropriate.
  • Manufacturing. Manufacturing standards, when used, include such things as construction, materials, ­dimensions, provisions for mounting, spacings between live parts, precautionary labels, and nameplate markings. Standards for materials may refer to tensile and compressive strengths, dielectric strengths, insulation resistance, and other pertinent physical ­properties.
  • Dimensions. Where dimensions are given for interchangeability purposes, alternate dimen­sions satisfying the other provisions of the standards publication may be capable of otherwise equivalent performance.
  • Performance. Performance standards, when used, cover characteristics such as temperature rise, interrupting capacity, voltage regulation, speed regulation, number of opera­tions without ­deterioration, and the ability to withstand specified conditions.
  • Testing. Testing standards, when used, include procedures for tests to determine com­pliance with manufacturing ratings and perfor­mance standards included in testing standards.
  • Marking. Marking standards, when used, generally require the manufacturer’s symbol and ­identification.
  • Application. Application information for the product may be included as part of the general standards or as a separate part of the NEMA standards publication.
  • Appendices. All appendices, which may include text, figures, and tables, are designated as authorized engineering information.
  • References to brand-name products. If it is necessary to refer to a particular device, a generic description should be used rather than a brand-name reference, unless such reference is essential for technical ­reasons and has been approved by NEMA Counsel.

The NEMA reference numbering system

NEMA standards are identified by an alphanumeric designator, a publication title, and a date.

The standard designator format typically includes:

  • A two-letter designation, based on NEMA product sections, that indicates the type of product or products covered by the standard. These designations are listed in the table below.
  • A numeric designation selected by the product section.
  • The publication (or reaffirmation) date

Examples:

“MG” refers to the Motors & Generators section of products

“AB” refers to the Molded Case Circuit Breakers section of products

MG 1-1999 AB 1-1999

NEMA's Product Scopes document contains a list of the alphanumeric designators in use. NEMA Product Scopes