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There is an argument between two engineers in the company on the use of FMC. Question arose when the contractor is trying to serve two vaccuum pumps that are more than 6 feet away. One engineer argues that NEC 348-20(A)(2) limits the use of flexible metal conduit for utilization equipment to less than 6 feet. The other engineer references paragraph 348.10 "Uses Permitted", it states that Flexible Metal Conduit, 1/2" and larger, may be installed in unlimited lengths, provided that an EGC is installed with the circuit conductors. And he also points out that the 6 ft length limitation for FMC is in reference to the U.L. rating which states that FMC in lengths over 6 ft are not approved as acceptable ground fault pathways and therefore when over 6 ft the FMC CANNOT be considered as the circuits equipment ground conductor (EGC). So, when using FMC in "unlimited lengths" as allowed by 348.10, an actual wire conductor EGC must be pulled with the circuit conductors. There have been lots of back and forth on this, and this might be a interpretation issue of the code. My question is: Who do you think is right. and what are your opinions on FMC when installed more than 6ft? Is it allowed under the condition that the engineer referenced? Sincerely, Joe
Hey Joe thanks for your question. It's fun to have engineers argue but the second one is more correct. Section 348.20 applies to flexible metal conduit (FMC) that is smaller than 1/2 inch (3/8). There is no length limitation for 1/2 inch and larger sizes in 348.10. If longer than 6 ft or the other conditions in 250.118(5) are not met then a wire type equipment grounding conductor must be installed as stated in 348.60.
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