Question
I am connecting 2 x 4 lay-in fluorescent fixtures in a suspended ceiling, and I am being told that you cannot daisy chain the connections to fixtures. I am using type MC cable with a ground and the lengths in some cases do exceed 6′. Am I in code violation and what code would reference this? — G. M.
Answer
This response is based on the information provided in the question. 2 x 4 lay-in style fluorescent luminaires are permitted to be wired with any branch circuit wiring method in chapter 3 of the NEC, depending on the type of building construction it is being installed in. You indicated that the luminaires are being wired using MC cable that is run from one luminaire to the next, using the ballast compartment as a junction box. As long as the luminaire is listed for this connection to the branch circuit, there is no Code requirement that would prohibit this installation. There is no length limitation in the Code for MC cable that is installed as a branch circuit.
Let’s go a step further for clarification. If we are talking about ⅜ in. fixture whips that include 18 AWG fixture wire, these are limited for use in 6 foot lengths to connect to a full size branch circuit in junction box typically located above the luminaire in a ceiling access space. The section that permits the use of these fixture whips (fixture tap conductors) is 210.19(A)(4), Exception 1(b) that refers to 410.117(C). This section permits the tap conductors in lengths not less than 18 inches and not longer than 6 feet, to connect to the branch circuit conductors. That being said, if the MC cable you refer to in your question is the factory whips that contain only tap conductors (18 AWG), then the installation described in the question is in violation of the NEC.
The next 6-foot restriction is in 250.118(5) and restricts flexible metal conduit from being used as an equipment grounding conductor in lengths exceeding 6 feet. Where an equipment grounding conductor is provided in flexible metal conduit, this length restriction is not applicable. There is no length limitation for flexible metal conduit unless it is ⅜ in. size and used for fixture tap conductor connections, once again the reference in 348.20(A)(2)(c) points to 410.117(C). However, the question does not deal with flexible metal conduit; it deals with MC cable installed as a branch circuit.
Article 330 covers MC cable and 330.10(A) provides the general uses for MC cable. Section 330.10(A)(1) indicates that MC cable can be used for branch circuits (without length limitations). Section 330.12, Uses Not Permitted, does not indicate that MC cable cannot be used in lengths longer than 6 feet. Type MC cable is recognized as providing equipment grounding conductor path when it meets the provisions in 250.118(10). There is no length limitation here either.
Summary: As long as the 2 x 4 lay-in luminaires are connected to the full size branch circuit (MC cable) conductors (usually 12 AWG with equipment grounding conductor), and the luminaire includes a junction box (ballast compartment) that is recognized for use as a junction point for branch circuit conductors (most lay-in luminaires are), then the installation as described would meet the minimum requirements in the NEC. If the question is, Can I daisy chain the luminaires with the ⅜ in. flexible metal conduit whips that typically are provided with the luminaires, the answer is no because these conductors are only tap conductors (usually 18 AWG) and not full size branch circuit conductors. See the information and Code sections provided in the first paragraph. I hope this effectively answers your question. As always check with the local authority having jurisdiction for any local code requirements that might modify or be in addition to the minimum requirements in the NEC. — Michael J. Johnston, CMP-5
