jar546
CBO
History and Evolution of NEC Section 250.140: Frames of Ranges and Clothes Dryers
The National Electrical Code (NEC) has evolved over the years to address the grounding requirements for electric ranges, wall-mounted ovens, counter-mounted cooking units, clothes dryers, and associated outlet or junction boxes. Prior to the 1996 edition of the NEC, it was common practice to use the grounded circuit conductor (neutral) as a grounding conductor for these appliances. This method often employed service-entrance (SE) cable with an uninsulated neutral conductor covered by the cable jacket. The key requirement was that the branch circuit originates at the service equipment to prevent neutral current from being imposed on metal objects downstream, such as pipes or ducts.However, the 1996 edition of the NEC marked a significant shift in grounding practices. The code began to prohibit the use of the grounded circuit conductor for grounding non-current-carrying metal parts of new appliance installations. Instead, it mandated the use of an equipment grounding conductor (EGC) sized in accordance with NEC 250.122. This change aimed to improve safety by ensuring a dedicated path for fault currents, reducing the risk of electric shock and fire hazards associated with neutral currents on grounded metal parts.
Detailed Evolution and Changes
Pre-1996 NEC: Before 1996, the NEC allowed the grounded circuit conductor to serve as a grounding path for electric ranges and clothes dryers. The SE cable method with an uninsulated neutral conductor was widely used, provided the branch circuit originated at the service equipment. This practice was designed to avoid imposing neutral currents on downstream metal objects, which could create dangerous conditions.Post-1996 NEC: The 1996 edition of the NEC introduced a pivotal change, disallowing the grounded conductor as a grounding method for new installations. This edition required new circuits supplying ranges and clothes dryers to include an EGC, thus ensuring that grounding for non-current-carrying metal parts was dedicated and reliable. This change significantly enhanced safety by providing a clear and consistent grounding path.
2000 NEC to 2020 NEC: The grounding requirements for existing branch circuits remained largely consistent from 2000 through the 2020 editions of the NEC. These codes allowed existing installations without an EGC to continue using the grounded conductor for grounding, provided certain conditions were met. These conditions included specific supply circuit configurations, minimum conductor sizes, and proper insulation of the grounded conductor. The primary objective was to maintain safety while accommodating older installations that could not easily be upgraded to include an EGC.
2023 NEC: The 2023 edition of the NEC further refines and clarifies the requirements for grounding frames of ranges and clothes dryers. It introduces two distinct subsections: 250.140(A) for equipment grounding conductor connections and 250.140(B) for grounded conductor connections. This restructuring enhances clarity and usability.
Special Focus on 2023 NEC Changes
The 2023 NEC incorporates significant changes to provide more flexibility and safety. One notable inclusion is the acceptance of copper-clad aluminum as a conductor material, addressing both cost and performance considerations. Additionally, the 2023 NEC adds a new condition for grounded conductors in Type SE service-entrance cables originating in non-service equipment. This condition requires that the grounded conductor be insulated or field-covered with listed insulating material to prevent contact with non-current-carrying metal parts, further ensuring safety.The 2023 NEC also removes the explicit "Exception" clause present in previous editions, integrating its provisions directly into the main text. This change simplifies the code and makes the requirements more straightforward. The revision ensures that grounding practices are up-to-date with current technology and safety standards, reflecting the NEC's ongoing commitment to electrical safety and reliability.
