I am looking for products to secure FMC (flexible metal conduit). I am having trouble finding any straps or hangers larger than trade size 3/8" that are labeled for anything other than EMT (electric metallic tubing) and RMC (rigid metal conduit)--typically they seem to be combination listed for both RMC/EMT.
UL-listed straps/hangers that accommodate the diameter requirements for FMC (refer to table 9.0 from UL 1 Ed 11.0 quoted below) and pull strength of greater than 228N (refer to UL 2239 Ed. 2.0 Section 7.4 quoted below) should be able to be used to secure and support FMC. Many UL-listed electrical cable ties (i.e. "zip ties") will meet these requirements.
Also, if you're looking for something a little sturdier, you should be able to use straps/hangers double-listed for EMT/RMC. It's still best to double-check with your inspector before starting work because they are technically not listed for FMC. However, it is easy to argue they meet the requirements for FMC based on the following information:
- The outer diameters of FMC are typically in between the outer diameter requirements for EMT and RMC per the applicable UL standards (see "UL 2239 Ed. 2.0 - Hardware for the Support of Conduit, Tubing, and Cable" below)
- The pull strength requirements for FMC are lower than both EMT and RMC for all trade sizes (see "Standards for Dimensions of FMC, EMT, and RMC" below)
UL 2239 Ed. 2.0 - Hardware for the Support of Conduit, Tubing, and Cable
UL 2239 Ed. 2.0 Section 7.4: "The force shall be as specified in Tables 6 – 9 for HANGERS, STAPLES, and STRAPS intended to secure or support non-flexible conduits and tubing. For flexible conduits or tubing or cables, the force shall be 228 N (50 lbf) for all sizes."
Below is a summary of what I found in the referenced tables 6-9 of UL 2239 Ed. 2.0 as force requirements to be listed as an EMT or RMC staple, strap, or hanger. Note: I list only the minimum force required which is always for the smallest trade size of EMT and/or RMC:
- Table 6 - Pull force requirements and LOAD RATINGS for STAPLES and STRAPS: Minimum of 334 N for 1/2" EMT -- this exceeds the 228 N required to be listed for FMC.
- Table 7 is the same as table 6, but in units of lbf instead of newtons.
- Table 8 Pull force requirements for HANGERS": Minimum of 667 N for 1/2 EMT -- this exceeds the 228 N required to be listed for FMC.
- Table 9 is the same as table 8, but in units of lbf instead of newtons.
Standards for Outer Dimensions of FMC, EMT, and RMC
It does appear to be true that the outer diameter of FMC does sit in between EMT and RMC as supported by the tables from the UL standards quoted below.
- FMC - Relevant portion of Table 9.1 Internal and external diameters in inches from UL 1 Ed 11.0:
- EMT - Relevant portion of Table 6.2 Dimensions and weight in USA customary units from UL 797A Ed 3.0:
- RMC - Relevant portion of Table 5.1 Dimensions of ERMC-S from UL 6 Ed 14.0: