The 1920 National Electrical Code

The 1920 National Electrical Code

With the 2020 National Electrical Code in the final stages of development, I thought it would be a good time to look back 100-years to the 1920 National Electrical Code and see what the electrical industry was up to so long ago.

The “Report of Electrical Committee” was presented to the NFPA membership on May 5, 1920 by Chairman Dana Pierce of New York. Mr. Pierce would go on to become the second president of Underwriters Laboratories in 1923 upon the death of UL’s founder, Mr. William Merrill and would continue to serve as president of the organization through the Great Depression until his death in 1934.

The thirty-one member Electrical Committee held its public hearing and committee meetings in New York on March 23-25, 1920 to complete work on the 13th edition of the National Electrical Code. The 1920 edition ended up being the last edition measuring 3½ inches by 5½ inches. The 1923 edition was expanded to 4 inches by 6¼ inches. This would be the size of the code until the 1953 edition. The 1920 NEC would also be the last edition to be arranged by “Class”. The 1923 NEC is the first edition to use the more familiar “Article” arrangement of the code though still significantly different from the Chapter-Article-Section format used in the code today.

The 1920 edition of the NEC has 216 pages and a total of 99 rules. As mentioned above, the code is arranged in six separate classes:

  • Class A – Generators, Motors, Switchboards, Etc. Includes electrical equipment of central stations, dynamo, motor and storage battery rooms, transformer sub-stations, etc. (Rules 1-11)
  • Class B – Outside Work, all systems and voltages (Rules 12-15)
  • Class C – Inside Work
    • General Rules, all systems and voltages (Rules 15A-19)
    • Constant-Current Systems (Rules 20-22)
    • Constant Potential Systems
      • General Rules, all voltages (Rules 23-25)
      • Low-Potential Systems, 600 volts or less (Rules 26-43B)
      • High-Potential Systems, 601 to 5,000 volts (Rules 44-46)
      • Extra-High-Potential Systems, over 5,000 volts (Rules 47-48)
    • Class D – Fittings, Materials and Details of Construction, all systems and voltages (Rules 49-84)
    • Class E – Miscellaneous (Rules 85-89)
    • Class F – Marine Work (Rules 90-99)

The 1920 NEC is the last edition of the code to include rules for Marine Wiring, Electric Cars, and Car Houses. These rules are not included in the 1923 NEC. The 1920 NEC is also the last edition to not have definitions included. The 1923 NEC added 30 defined terms in a new Article 1. Definitions. Here are a few of the other interesting facts about the 1920 NEC:

  • The low-potential voltage threshold was increased to 600 volts from 550 volts. Rules for 600 volts and less and for over 600 volts have remained the standard until the 2017 NEC moved that value up to 1,000 volts.
  • Driven rods (ground rods) were not yet recognized by the code. “Artificial grounds” in the 1920 edition included driven pipes or buried plates (Rule 15A.). The 1918 edition added driven pipes and the 1923 edition added driven rods. The “25-ohm” rule first appeared in the 1918 edition. Article 250 now contains the rules for grounding and bonding.
  • Rule 8. Motors was expanded by adding requirements for motor overload protection, sizing and protection of conductors for motors, and motor disconnecting means (switch). These rules continue to exist in Article 430, Part IV, V, and IX.
  • A “Standardized Stranding” table was added to Rule 18. Table of Allowable Capacities of Wires. This can now be found in Chapter 9, Table 8.
  • Rule 19. Switches, Cut-outs, Circuit-breakers, etc. was expanded to identify the number of overload trip coils required based on the wiring system configuration. This rule still exists in Article 240.
  • Rule 25. Heating Appliances was changed from Heating Devices as used in previous editions of the code. These rules are now found in Articles 422 and 424.
  • Rule 26n. Wires for Conduit Work was revised stating wires “must be stranded for all conductors No. 6 B. & S. gage and larger”. This rule is now located in 310.106(C).
  • A new Rule 35A. Equipments in Extra Hazardous Locations was added to the code. There are more requirements for electrically operated organs than for hazardous location in the 1920 NEC. The new requirements in Rule 35A. can still be found In Article 500 today.
  • New requirements were added to Rule 38A. Moving Picture Exchanges, Factories and Studios, and Moving Picture Equipments covering equipment for use only in fireproof booths and equipment for use without fireproof booths. These new rules are now located in Articles 530 and 540.
  • A new Rule 43A. Elevator Wiring was added to the code that includes 11 special requirements (43A.a through 43A.k). Elevators are now covered under Article 620.
  • A new Rule 43B. Isolated Light and Power Equipments for less than 50 volts was added to the code that includes a definition and just one requirement. Article 720 now covers circuits and equipment operating at less than 50 volts.
  • Rule 86 was renamed from Wireless Telegraph Apparatus to Radio Signaling Apparatus laying the ground work for today’s Article 810 and 820.

I wonder if the Electrical Committee of 1920 could even begin to imagine the scale and scope of the 2020 National Electrical Code with its 9 Chapters, 155+ Articles, and nearly 900 pages in an 8½ x 11 inch format. The first 20-years of code progress from the 1897 edition to the 1920 edition were impressive. The next 100-years of code development are truly spectacular.

The National Electrical Code is more than a list of rules for electrical installations. It contains the history of advancements in technology, cultural trends in safety, and the growth and decline of industries.

Here’s to the 13th and 55th edition of the National Electrical Code. 123-years strong and only getting better with age.


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