Electrical Wiring Materials and Proper Installation

There are many different types of wiring materials. Installations of these components are different depending on the usage. Although you may be able to use different wire / conductor types for similar applications; there are specific recommendations for these types of branch circuit wiring. Here are the most common types of wiring and how they are normally used. Armored Cable (AC) has been used for many years and still in use today. The conductors are plastic (cloth for older applications), and the outer covering is metal. Rigid Metal Conduit is designed for protection of conductors. RMC ranges in size from ½” to 4”. Non-Metallic Tubing (ENT) is a flexible corrugated tube designed for protection of conductors. ENT is not approved for exterior locations. Check with the manufacture. Liquidtight Flexible Conduit (LFC) is made from PVC and can be installed in all locations. Often found on exterior HVAC equipment, swimming pools, & hot tubs.
Rigid Polyvinyl Chloride Conduit (RNC) is not the same as plumbing pipe and cannot be used as such. Plumbing PVC may not be used as RNC either. It comes in two wall thicknesses; Schedule 40 or 80. Underground Feeder (UF) is designed for wet locations. It is normally gray in color. Nonmetallic (NM) is most common in modern construction since around 1940. Early versions of NM from around 1920 – 1940 had cloth sheathing instead of the modern PVC sheathing. NMC has a coating that is non conducting, flame-resistant, and moisture resistant. NMC is approved for damp environments. So what are some things home inspectors should look for:
 
  • AC cable should only be used indoors
  • AC conductors should have an anti-short bushing at every end
  • AC should be supported every 4 ½ feet and within 1 foot from boxes and terminations
  • RMC can be installed in all locations including into concrete
  • RMC should be supported every 10’ and within 3’ from boxes & terminations
  • ENT should be supported every 3 feet
  • LFC should be supported every 4 1/2’ and within 1’ from boxes and terminations
  • RNC may be installed in all locations including burial and embedded in concrete
  • RNC should be supported every 3 feet for 1” and smaller sizes, 5’ for 1¼” and larger sizes and within 3 feet from boxes and terminations
  • UF cannot be embedded in concrete
  • UF may not be used for swimming pool, hot tub, or spa wiring
  • NM should only be located in dry locations only and not below grade
  • NM should not be installed inside of conduit that is buried
  • NM may not be embedded in concrete or in conduit embedded in concrete.
  • NMC is approved for damp locations
  • All electrical conductors should be protected by strike plates if closer than 1 ¼” from the edge of any framing member
  • Burial depth is as follows: UF / MC is at least 24”, RMC at least 6”, LFC is at least 18”, GFCI protected residential branch circuits of 20 amps or less may be buried at least 12 inches regardless of the wiring method. 
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