News



4.1.2019

Threadless Fittings for Use with Metal Conduit and EMT


When planning a new construction project, renovation, or an addition to an existing structure, you need to choose which wiring method is the most effective. You’ll need to take into consideration physical protection, approved for exposed installations, approved for use in wet locations, offer corrosion resistance, and/or serve as an equipment grounding conductor. Metal conduits (Rigid Metal Conduit, Intermediate Metal Conduit, and Electrical Metallic Tubing) will meet all these various installation needs, however, selecting the proper fitting for installation is an integral part of ensuring the metal conduit’s performance. This decision can be made simpler if you know what product or package markings to look for and the proper installation steps for such fittings.

One of the major benefits of metal conduit is that it can be used as an equipment grounding conductor per National Electrical Code® (NEC®) Sections 342.60, 344.60, 358.60 and 250.118(4). Since metal conduits can be used as an equipment grounding conductor, all fittings and connectors associated with them must pass a resistance and continuity test to show that they can provide an effective grounding path to receive a UL listing to safety standard 514B. All metal fittings for use with non-flexible metal raceways must pass both of the following tests:

  1. Resistance test – For this test, the fitting/connector is assembled for its purpose, either joining two pieces of metal conduit or attaching a piece of metal conduit to a box. The resistance is measured between two points on the assembly as a specified amperage is passed through the assembly. The resistance measured cannot exceed a specific amount or the fitting/connector will not pass.
  2. Current test – For this test, a high current is passed through the assembly for a specific period. If the fitting can hold the current for the specified amount of time without showing any signs of damage, a continuity test is performed. The fitting must show that it can continue to provide continuity after the current test to pass this portion of the listing.
  3. Any fitting that is Listed to UL 514B for use with metal raceways is listed to be used in an equipment grounding conductor raceway. To make sure that the fitting has been tested for carrying current, make sure the label states “Listed to UL 514B and/or CSA C22.2 no. 18.3-12 for use with Rigid Metal Conduit (RMC), Intermediate Metal Conduit (IMC), or Electrical Metallic Tubing (EMT)”.

Encasement of metal conduit in concrete requires that the fittings being used are listed to UL 514B and/or CSA C22.2 no. 18.3-12 as Concrete-tight. Look for the listing mark and “Concrete-tight” on the package or label.

  • Compression type fittings are concrete-tight if they are listed to above mentioned UL or CSA standard.
  • Set Screw and other type of threadless fittings may be required to be taped to be concrete-tight. If this is the case, the markings on the package will state “Concrete-tight when taped” or something similar.

Installing metal conduits below grade, in concrete slabs, direct contact with earth, in locations subject to saturation with water and other liquids, or in unprotected locations exposed to weather is considered a “Wet Location” by the National Electrical Code®. To ensure use of the proper fitting in these environments, look for the package or label to state “Wet Locations” and listed to UL 514B and/or CSA C22.2 no. 18.3-12.

  • Sometimes the package may say “Raintight” instead of “wet location” but should still state it is listed to the UL or CSA standard.

Once you have confirmed the appropriate markings on the conduit, the next step is proper installation of the fitting. The bullet points below will cover proper installation procedures for set-screw and compression type fittings for use with metal conduits. Also outlined are some of the requirements the fitting must pass to receive certification by UL and ensure that when installed and maintained properly, the fitting will not separate.

Set-Screw Type Fittings

When installing set-screw type fittings, the industry recommended practice is to tighten the screw/bolt to the torque that can be applied by the screwdriver itself. Do not over tighten by using a wrench or any other tool to help apply more torque to the screw. Performance of the fitting may be reduced by over tightening as much as it can be by under tightening.

When set-screw fittings are tested by UL, the following torque values are used unless a manufacturer specifies a torque value:

  • The torque value used for a No. 8 screw is 20lbf-in
  • The torque value used for a No. 6 screw is 12lbf-in
  • The torque value used for all other size screws is 35 lbf-in
  • After the fitting is tightened to the proper torque, UL performs a pull test anywhere from 300-1000 lbf on the assembly to ensure the fitting does not separate
  • If a manufacturer provides torque values in their installation procedures for the fitting, these values should be used when tightening the fitting

Compression Type Fittings

The industry recommended practice for installing compression type fittings is to tighten the nut the maximum allowed by hand and then wrench tighten an additional one to two turns.

When compression fittings are tested by UL, the following torque values are used unless a manufacturer specifies a torque value:

  • ½ trade size fitting is tightened to 300 lbf-in
  • ¾ trade size fitting is tightened to 500 lbf-in
  • 1 trade size fitting is tightened to 700 lbf-in
  • 1¼ trade size fitting is tightened to 1000 lbf-in
  • 1½ trade size fitting is tightened to 1200 lbf-in
  • 2-4 trade size fittings are tightened to 1600 lbf-in
  • After the fitting is tightened to the proper torque, UL performs a pull test anywhere from 300-1000 lbf on the assembly to ensure the fitting does not separate.
  • If a manufacturer provides torque values in their installation procedures for the fitting, these values should be used when tightening the fitting

Metal conduit when installed properly, is an economical, flexible, effective, and long-lasting electrical raceway system. Please contact the Atkore industry affairs department if you have questions regarding the type of location and/or installation procedures for metal conduit and associated fittings, connectors, and accessories.