National Electrical Installation Standards

Standards as High as Your Own

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Tuesday, June 2, 2020

Question:

Greetings,

Is there a limit on how many extension rings are allowed on a four square junction box or any J-box for that matter?

Lucas Koomen

A

Answer:

Hello Lucas,

Thanks for participating. The installation instructions for electrical equipment typically provide the requirements and any limitations on certified electrical equipment. Listed box extensions are covered in UL Product Category QCIT which indicates extension rings are suitable for extending properly secured flush- or surface-mounted boxes. One or more extensions may be used. An extension ring is intended to increase the box depth, volume, or both. See the following URL for more product certification information: https://iq.ulprospector.com/info/ 

The number of extensions that can be installed on a box is not provided and may be addressed by the manufacturer's installation instructions. There are also other NEC requirements for length of free conductor that must be provided, such as in Section 300.14, which is generally 6 inches of free conductor beyond the edge of the box opening. Section 314.22 provides additional information about installing box extensions securely and complying with equipment grounding requirements. Box extensions are often used for extending a flush-mounted box so a surface raceway adn be installed from it. Section 110.12 may also come into play regarding workmanship and the final approvals rest with the applicable authority having jurisdiction.

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IMPORTANT NOTICE: Unless the question requests a response based on a specific edition, all answers are based on the latest edition of NFPA 70® National Electrical Code®.

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