Article 358 of the National Electrical Code (NEC) 2023 covers the requirements for electrical metallic tubing (EMT). This type of conduit is used to protect electrical wires and cables from physical damage and to provide a grounded path for electrical currents. EMT is typically used in residential and commercial applications where flexibility, durability, and ease of installation are important.
The NEC provides detailed guidelines for the installation and use of EMT to ensure the safety and reliability of electrical systems. The requirements outlined in Article 358 cover the materials, dimensions, installation, and maintenance of EMT.
Materials
The materials used to manufacture EMT must comply with the requirements set forth in Article 358. EMT is made of a thin-walled metal tube, usually made of steel or aluminum, that is coated or galvanized to prevent corrosion. The conduit must also be free from any defects that could affect its strength or flexibility, such as cracks, splits, or holes.
Dimensions
Article 358 sets forth specific dimensions for EMT to ensure its compatibility with other electrical components and to facilitate proper installation. The diameter of EMT must be at least 1/2 inch, and it cannot exceed 4 inches. The walls of the conduit must be uniform in thickness and cannot be less than the minimum values specified in the NEC.
Installation
Proper installation of EMT is essential for the safety and reliability of electrical systems. Article 358 provides detailed guidelines for the installation of EMT, including the use of fittings, supports, and expansion joints.
Fittings
Fittings are used to connect sections of EMT and to change the direction of the conduit. The NEC requires that fittings be made of the same material as the conduit and that they be compatible with the type and size of the conduit being used. Fittings must also be installed in accordance with the manufacturer’s instructions and the requirements of the NEC.
Supports
EMT must be supported at regular intervals to prevent sagging and to ensure proper alignment. The NEC specifies the maximum distance between supports based on the size and weight of the conduit. Supports must be made of materials that are compatible with the conduit and must be securely attached to the building structure.
Expansion Joints
Expansion joints are used to compensate for the expansion and contraction of the conduit due to temperature changes. The NEC requires that expansion joints be installed at intervals determined by the manufacturer or engineer, based on the length and temperature range of the conduit. Expansion joints must also be compatible with the material and size of the conduit.
Bending
EMT can be bent to follow the contours of the installation area. The NEC specifies the minimum radius of bends based on the size and type of conduit being used. Bends must also be made in accordance with the manufacturer’s instructions and the requirements of the NEC.
Grounding
EMT must be grounded to provide a safe path for electrical currents. The NEC requires that EMT be connected to a grounding conductor using approved fittings and connectors. The grounding conductor must also be continuous and unbroken.
Maintenance
Regular maintenance is important to ensure the continued safety and reliability of EMT. Article 358 requires that EMT be inspected periodically to ensure that it is free from defects, corrosion, and other damage. Any damaged or defective conduit must be replaced immediately to prevent hazards.
Conclusion
Article 358 of the NEC 2023 provides detailed guidelines for the installation and use of electrical metallic tubing. EMT is a versatile and durable option for protecting electrical wires and cables in residential and commercial applications. The requirements set forth in Article 358 cover the materials, dimensions, installation, and maintenance of EMT to ensure the safety and reliability of electrical systems.
It is essential to follow the guidelines set forth in Article 358 to ensure the proper installation and use of EMT. Failure to do so can result in hazards such as electrical shock, fire, and damage to equipment. Regular maintenance is also important to prevent damage and ensure the longevity of the conduit. By following the guidelines set forth in Article 358, electrical professionals can ensure the safe and reliable use of EMT in their installations.
Electrical metallic tubing has several advantages over other types of conduit, including its flexibility, durability, and ease of installation. EMT is also lightweight and can be easily cut and bent to fit the contours of the installation area. It is also resistant to corrosion, which makes it a popular choice for outdoor and wet environments.
When choosing between different types of conduit, it is important to consider the specific requirements of the installation and to consult the NEC guidelines. In some cases, a combination of EMT and other types of conduit may be necessary to provide the optimal level of protection and flexibility.
In conclusion, Article 358 of the NEC 2023 provides important guidelines for the installation and use of electrical metallic tubing. EMT is a versatile and durable option for protecting electrical wires and cables in residential and commercial applications. By following the guidelines set forth in Article 358, electrical professionals can ensure the safe and reliable use of EMT in their installations.