Tuesday, December 2, 2025

when did we change from 110 to 120 and from 220 to 240?

So, for example, if your home was built before the 1960s and still has the original wiring in it (or hotel or other building then it has a higher chance of burning down unless all the wiring has been updated since then I guess? What do you think?

begin quotes: 

 
The change from 110V to 120V and from 220V to 240V in the US was a gradual process that occurred in the
mid-20th century, with 120V/240V becoming the standard in the 1960s and formally adopted by the National Electrical Code (NEC) in 1968 and again in 1984. The transition was driven by the development of more efficient incandescent bulbs and a need for higher, more uniform standards, though the older terminology persists due to historical reasons and for convenience in describing voltage tolerances. 
  • Gradual transition: The nominal voltage in the US increased gradually from 110V to 115V, 117V, and finally to 120V by the mid-1960s.
  • Formal adoption: The change to the 120V standard was formalized by the NEC in 1968, with a reinforcement in 1984.
  • Continued use of old terms: The terms 110V and 220V are still commonly used because the change was gradual and the older terms are familiar, but all modern US outlets have a nominal voltage of 120V/240V.
  • Reasons for the change: The voltage increase was driven by the need for a more standardized voltage and the development of metal filament lamps that could run on higher voltages. The change also led to some safety and efficiency improvements in the electrical system. 

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