All references are based on the 2023 edition of the NEC.
Lame Use of LFMC
Too Close for Comfort!
If we read through all of Art. 350, we will find no rules that permit using liquidtight flexible metal conduit (LFMC) to support an outlet box. However, we will also find no rules that prohibit this practice. So, where does this leave us when trying to determine if the installation in this photo is Code-compliant or not? Well, if we take a look at Sec. 314.23, we will find several rules about securing and supporting boxes.
For outlet boxes containing devices such as switches or receptacles, Sec. 314.23(F) provides requirements for raceway-supported enclosures. The size of the box in the photo complies with the requirement to not exceed 100 cu. in. as specified in that Section, but using the LFMC to support that box is not permitted. Two conduits such as rigid metal conduit (RMC) or intermediate metal conduit (IMC) must be threaded wrench tight into the enclosure and then be secured within 18 in. of the enclosure to provide a Code-compliant installation. Neither of the two exceptions to Sec. 314.23(F) applies to the installation in the photo. Using LFMC to support a box does not comply with Sec. 314.23(F).
On a more positive note, at least the installer installed a cover that complies with Sec.406.9 for receptacles installed in wet locations.
The workers who repaired the roof for this building came close to getting a snappy and sparky surprise. If any one of those long screws penetrating the roof had been positioned a little differently, there could have been a big kaboom. Those self-tapping screws could have easily penetrated the box or electrical metallic tubing (EMT) and destroyed any wiring contained in them. Thankfully, all of the screws missed hitting any parts of the electrical installation.
Those long screws are a good example of why Sec. 300.4(E) requires cables, raceways, and boxes to be installed so there is at least 1½ in. of space between the lowest part of the metal roof decking and the top of the cable, raceway, or boxes. Exception No. 1 allows rigid metal conduit (RMC) or intermediate metal conduit (IMC) to be installed without the 11/2-in. spacing. Exception No. 2 eliminates the 1½-in. spacing requirement where the metal roof is covered with a concrete slab at least 2 in. thick. While luminaires are not covered by Sec. 300.4(E), Sec. 410.10(F) requires the same 1½-in. spacing for luminaires installed under any roof decking where subject to physical damage with one exception for roofs covered with a concrete slab at least 2 in. thick.
