Essential Tips for Working With EMT - What Every Electrician Needs to Know
Table of Contents
- Introduction to EMT (Electrical Metallic Tube)
- Uses of EMT in the NEC (National Electrical Code)
- Permitted uses of EMT
- Exposed environments
- Concealed environments
- Concrete or direct burial
- Not permitted uses of EMT
- Environments subject to physical damage
- Using EMT as support for luminaires or fixtures
- Importance of dissimilar metals in EMT
- Sizes of EMT
- Bending radius of EMT
- Reaming the ends of EMT
- Securely strapping and supporting EMT
- Couplings and connectors for EMT
Introduction to EMT (Electrical Metallic Tube)
EMT, or Electrical Metallic Tube, is a type of tubing commonly used in electrical installations. It serves as a conduit for passing wires through and is often referred to as conduit. While it is most commonly made of thin-walled steel, there are also stainless and aluminum versions available. EMT can be used in exposed or concealed environments, as well as in concrete or direct burial applications. However, it is important to consider the limitations of EMT, as it should not be used in environments where it is subject to physical damage, or as a support for luminaires or fixtures.
Uses of EMT in the NEC (National Electrical Code)
The NEC provides guidelines for the permissible uses of EMT in electrical installations. These guidelines ensure safety and compliance with electrical codes. Here are some of the permitted uses of EMT:
Exposed environments: EMT can be installed in exposed environments, such as running along walls, providing a protective raceway for wiring.
Concealed environments: EMT is also suitable for concealed applications, where it can be installed behind walls to protect and route electrical wiring.
Concrete or direct burial: In certain situations, EMT can be embedded in concrete or directly buried in the earth. However, specific types of EMT, such as stainless or galvanized, should be used to withstand the corrosive nature of the ground.
It is important to note the uses that are not permitted for EMT. EMT should not be installed in environments where it is likely to be physically damaged, such as areas prone to impact or crushing. Additionally, EMT should not be used as a support for luminaires or other fixtures. Proper support should be provided to ensure the stability and integrity of the installation.
Importance of Dissimilar Metals in EMT
When using EMT, it is crucial to consider the interaction of dissimilar metals. Different metals have varying levels of reactivity, which can lead to corrosion and degradation. Aluminum, for example, is highly reactive and can corrode when in contact with other metals. Therefore, it is essential to use appropriate fittings, couplings, and straps specifically approved for use with the type of metal being used.
Stainless steel, on the other hand, is less prone to rusting but can still be affected by certain environmental factors. When using stainless steel EMT, it is important to ensure that all components are made of stainless steel or compatible materials to prevent corrosion.
Sizes of EMT
EMT comes in various sizes, and the NEC specifies the approved sizes for electrical installations. Generally, EMT must have a diameter of either 1/2 inch or 4 inches. It is crucial to adhere to these size specifications to ensure proper installation and compliance with electrical codes.
Bending Radius of EMT
The bending radius of EMT is an important factor to consider when working with this type of tubing. Bending the EMT beyond its specified radius can result in kinking or damage to the conduit. The NEC stipulates that the total bend angle within a conduit run should not exceed 360 degrees. It is commonly recommended to limit the number of bends in EMT to avoid difficulties in wire pulling and to maintain the structural integrity of the conduit.
Reaming the Ends of EMT
After making a cut in a piece of EMT, it is essential to ream the ends of the conduit to remove any burrs or sharp edges. This helps ensure a smooth surface, preventing damage to wires during installation. Reaming can be done using various tools, such as specialized reaming tools, channel locks, or needle-nose pliers. Proper reaming of EMT ends is necessary to create a safe and suitable pathway for electrical wiring.
Securely Strapping and Supporting EMT
Properly securing and supporting EMT is crucial for the safety and longevity of the electrical installation. Within 3 feet of a termination point, whether it is a box or panel, the conduit must be securely strapped. Generally, the rule of thumb is to install a strap or support every 10 feet. However, within 10 feet of a termination point, the strap or support should be within 3 feet. This ensures stability and prevents excessive movement or possible damage to the conduit.
There are exceptions to the strapping requirements. If the conduit is installed behind an inaccessible area, such as inside a wall, strapping may not be practical. Likewise, if the building or structure does not allow strapping within 3 feet of a termination point, it is acceptable to strap within 5 feet instead. These exceptions should be carefully considered and followed while ensuring compliance with local codes and regulations.
Couplings and Connectors for EMT
When connecting two pieces of EMT or terminating a conduit run into a box, it is crucial to make up the couplings and connectors tightly. This ensures a secure and reliable connection, maintaining the continuity of the conduit system. Loose or improperly tightened couplings and connectors can disrupt the integrity of the electrical installation and compromise safety. Set screw-style couplings should have all screws tightened, while weatherproof couplings should be tightened on both sides using channel locks. Following these guidelines for couplings and connectors helps to ensure a reliable electrical conduit system.
In summary, EMT is a versatile tubing used in electrical installations for housing and protecting electrical wiring. By understanding the uses, limitations, and guidelines for working with EMT, electricians can ensure safe and compliant installations. Proper selection of sizes, consideration of dissimilar metals, attention to bending radius, reaming of ends, secure strapping, and tight coupling connections are all crucial aspects of working with EMT.
【Highlights】
- EMT (Electrical Metallic Tube) is a type of tubing used in electrical installations.
- EMT provides a protective conduit for wires and can be used in exposed or concealed environments.
- EMT should not be used in areas subject to physical damage or as support for luminaires or fixtures.
- Dissimilar metals must be carefully considered when using EMT to prevent corrosion.
- The size, bending radius, reaming, and secure strapping of EMT are important considerations for proper installation.
- Couplings and connectors must be tightly made up to maintain the integrity of the conduit system.
【FAQ】
Q: Can EMT be used in outdoor applications?
A: Yes, EMT can be used in outdoor applications as long as it is the appropriate type, such as stainless or galvanized, and is properly supported and protected from physical damage.
Q: Can EMT be bent without special tools?
A: EMT can be bent using a variety of tools, including hand benders, mechanical benders, or conduit bending machines. The specific tool required depends on the size and angle of the bend needed.
Q: Are there any restrictions on the number of bends in EMT?
A: Yes, the NEC specifies that the total bend angle within an EMT conduit run should not exceed 360 degrees. It is important to limit the number of bends to maintain the integrity of the conduit and ease wire pulling.
Q: Can EMT be used as an equipment grounding conductor?
A: Yes, EMT can be used as an equipment grounding conductor under certain conditions. However, it is crucial to ensure that all couplings and connectors are tightly made up to maintain continuity throughout the conduit system.
Q: What is the maximum length of EMT that can be installed before requiring additional supports?
A: Generally, it is recommended to install a strap or support every 10 feet of EMT. However, within 3 feet of a termination point, such as a box or panel, a strap should be placed to ensure proper support.
