Fielding Questions: Can liquidtight flexible metal conduit be installed in a ceiling?

Shutterstock / Vinap
Shutterstock / Vinap
Published On
Sep 15, 2022

Some of the most common questions people bring up to me sound like, “Does the National Electrical Code permit this very specific thing to be done?” The email or message usually doesn’t state whether the installation is being contemplated or has already been completed.

There are times when I know the installation has already been completed simply by how adamantly the person tries to defend it. This is especially apparent when the installation doesn’t follow NEC requirements and the person argues with me vehemently that it is acceptable. At this point, I usually ask if the installation is already complete. The answer invariably comes back as yes, and the electrical inspector has written a notice of violation or issued a red tag.

Complex issues and answers

I have had questions dealing with complex issues where the fix will be expensive and complicated. For example, I had an electrical engineer ask me if hallway convenience receptacles, general lighting and other similar types of general loads in a large office complex could be directly supplied from an emergency panelboard. He also asked if the emergency loads could be installed in the same raceways and boxes as the normal circuits. I said no, and referred him to the definition of emergency systems in 700.2 for the permissible loads and separation requirements in 700.10(B) in the NEC.

I told him that a panelboard would be required for the normal and emergency loads. He told me he didn’t agree with my assessment and interpretation of the NEC. I replied that it would be a very easy fix to redo the plans and provide the appropriate separation of circuits and separate panelboards to bring it up to Code.

That is when he told me that the project was totally installed and ready for final inspection, with a violation notice for noncompliance with the NEC for the reasons I had stated. He was not happy with my answer, but safety must never be compromised.

Providing alternative solutions

There are times when my answer to a question will clarify an issue; sometimes a simple fix is to provide an alternative to what normally would be a violation. As an example, I was driving back from giving a workshop in Las Vegas. An electrical contractor friend of mine called with a unique question about an installation he had done involving 10 liquidtight flexible metal conduits installed from the air-conditioning compressor units on the roof into the ceiling area of an office building to connect individual fan coil units.

The ceiling area was not originally an “other space for environmental air (plenum),” according to the plan, but it had been converted to an HVAC return air space. The office building had been given permission for temporary occupancy before the final inspection.

My friend wanted to know, “Is the installation of the liquidtight flexible metal conduit a violation of the NEC?” He already knew that it was, but he also knew that having to replace the conduit would involve major disruption for the occupants. I confirmed that it was a violation of 300.22(C)(1) and would need to be replaced.

He was not happy about the answer, but totally understood the issue of not installing a wiring method with a nonmetallic jacket in an “other space for environmental air (plenum).” A combustible jacket could start a fire and spread products of combustion throughout the facility, creating smoke inhalation hazards to occupants.

About an hour after I gave him the bad news, I called him back with a possible fix for his problem that wouldn’t compromise safety. Article 360 covers flexible metallic tubing that is defined as “a metal raceway that is circular in cross section, flexible, and liquidtight without a nonmetallic jacket.” It is permitted in dry, concealed and accessible locations and lengths of 6 feet or less. I told him to work with the building’s owners and the electrical inspector to obtain special permission to remove the liquidtight flexible metal conduit’s jacket in the return air ceiling, and since it was already in lengths of 6 feet or less, he would not have to totally disrupt the customer while still complying with the NEC.

He did call the owner and the electrical inspector, who agreed to this safe, unique fix for the problem.

About the Author

Mark C. Ode

Fire/Life Safety, Residential and Code Contributor

Mark C. Ode is a lead engineering associate for Energy & Power Technologies at Underwriters Laboratories Inc. and can be reached at 919.949.2576 and Mark.C.Ode@ul.com.

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