Answer: The 2011 National Electrical Code (NEC) allows the direct burial of all three products as noted in their respective Articles:
Galvanized Steel RMC Section 344.10 (B) Corrosion Environments. Galvanized steel RMC, elbows, couplings, and fittings “shall be permitted to be installed in concrete, in direct contact with the earth, or in areas subject to severe corrosive influences where protected by corrosion protection and judged suitable for the condition.”
IMC Section 342.10 (B) Corrosion Environments. Galvanized steel IMC, elbows, couplings, and fittings “shall be permitted to be installed in concrete, in direct contact with the earth, or in areas subject to severe corrosive influences where protected by corrosion protection and judged suitable for the condition.”
EMT Section 358.10 (B) Corrosion Protection. Galvanized steel EMT, elbows, couplings, and fittings “shall be permitted to be installed in concrete, in direct contact with the earth, or in areas subject to severe corrosive influences where protected by corrosion protection and approved as suitable for the condition.”
Members of the Conduit Committee of the Steel Tube Institute apply a zinc coating to galvanize steel RMC, IMC and EMT. Therefore, these products are “protected by corrosion protection” as the Code requires. However, in severely corrosive environments, the designer or AHJ may decide to require additional or supplementary protection.
American Fitting’s alloy steel conduit electrical fittings are industrial zinc plated with a chromate finish, therefore, meet the code requirements. Fittings may also be galvanized plated. Also, see the chart below outlining the chemical and physical properties of our fittings compared to diecast or malleable iron.
Underwriters Laboratories’ Guide Information for Electrical Equipment
The White Book 2011 contains information relating to limitations or special conditions applying to products listed by UL. The directory states that galvanized steel RMC and IMC do not generally require supplementary corrosion protection when installed in the soil unless 1. Soil resistivity is less than 2000 ohm-centimeters. 2. Local experience has confirmed that the soil is extremely corrosive.
(Note: Soils producing severe corrosive effects have low electrical resistivity, expressed in ohm-centimeters. Local electric utilities commonly measure the resistivity of soils. The authority having jurisdiction (AHJ) has the authority to determine the necessity for additional protection.) EMT in direct contact with the soil generally requires supplementary corrosion protection. However, local experience in some areas of the country has shown this to be unnecessary.
It is recommended that all direct burial fittings for Rigid, IMC, or EMT conduits be of Rain Tight Construction. This will ensure the integrity of your connection. Consider the physical and chemical properties and construction of direct burial conduit fittings to ensure you have selected the best material for your installation.
What Advantages Does Steel Have Over PVC for Direct Burial?
The use of PVC should not be considered when you require your wireway to be tough, durable, with high tensile strength. Additionally, steel will withstand the effects of environmental trauma from weather, erosion, or blunt force. For Rigid Conduit you would require Sch 80 in PVC, this is heavier than standard PVC and the cost analysis vs. steel should be considered. Steel is fully recyclable and is more friendly for our environment that PVC – A basic building block of polyvinyl chloride is chlorine, and chlorine production releases dioxins into the environment. Steel is fully fire-resistant and in the event of combustion will not be the subject to melt or cancer-causing fumes.
PVC pipe contracts when exposed to the sun or extreme temperatures. In addition, in extreme cold, PVC conduit can become brittle and is more susceptible to physical damage.
The Perception that Plastic Pipe Saves Money on Materials.
“PVC is so much more affordable,” says Vice. But recent reports, highlighted in “The Economics of Phasing Out PVC,” published by the Global Development and Environment Institute at Tufts University, Somerville, Mass., say this isn’t necessarily true.
According to the reports, life-cycle costs often favor alternatives. A strict comparison of purchase prices, or even installed costs, of PVC and alternatives, may give a misleading impression that PVC is more affordable. “Some of the alternatives have higher initial purchase prices than PVC products, but are actually less expensive over the useful life of the product,” reads the study.
Steel conduit and steel conduit fittings are ideal for direct burial applications including systems for:
- Cable, data and communication lines
- Institutional, commercial, industrial buildings
- Residential applications, & service entrances
- Street and highway underground feeds
- Transportation systems – subways, bridges, tunnels, airports<
- Water and wastewater treatment plants
- Mines and mills
Analysis Chemical & Physical Properties of
AMERICAN FITTINGS Steel Electrical Fittings Suitable for Direct Burial vs. Die Cast or Malleable Iron
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All AMFICO steel fittings are industrial zinc plated with a chromate finish. This on top of alloy steel provides a unique blend of corrosion resistance in most conditions including direct burial. While not critical all American Fittings Rigid and Liquid Tight Fittings can be galvanized such the design engineer set that as a requirement.
Have a specific application requiring electrical fittings for direct burial or other environmental situation? Contact Us Today we are happy to assist in any questions or requirements.