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This ¾-in. rigid metal conduit (RMC) shows a severe case of corrosion. Although it was properly installed long ago under an overpass along a major roadway, it has been subjected to many salt baths during the winter months when the roadway above is treated with sand and salt to prevent icing. So the question arises, "Should the designer or installer have done anything differently in anticipation of this future problem?"
Here are three specific Code sections we can reference that should apply to this type of installation.
- As noted in 110.11, "Unless identified for use in the operating environment, no conductors or equipment can be located in damp or wet locations; where exposed to gases, fumes, vapors, liquids, or other agents that have a deteriorating effect on the conductors or equipment; or where exposed to excessive temperatures."
- Section 110.12(B) covers the integrity of electrical equipment and connections. More specifically it states, "Internal parts of electrical equipment, including busbars, wiring terminals, insulators, and other surfaces, must not be damaged or contaminated by foreign materials such as paint, plaster, cleaners, abrasives, or corrosive residues." The rule goes on to state that "no damaged parts may adversely affect safe operation or mechanical strength of the equipment." One can clearly see in the photo that the mechanical strength of this RMC has definitely been compromised over the years.
- Section 300.6 also covers protection against corrosion and deterioration. "Raceways, cable trays, cablebus, auxiliary gutters, cable armor, boxes, cable sheathing, cabinets, elbows, couplings, fittings, supports, and support hardware must be of materials suitable for the environment in which they are to be installed." In addition, this statement appears in 300.6(A), "Where corrosion protection is necessary and the conduit is threaded in the field, the threads shall be coated with an approved electrically conductive, corrosion resistant compound."