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I'm adding some more circuits to a finished garage. Most of the wiring is going in the joist cavities (or in EMT otherwise). Perpendicular to the joists, in the middle of the garage, is a steel I-beam. I can't (don't want to) drill through that. To get across the I-beam, I span it with a fluorescent fixture (non-hanging with built-in J-box). The lighting circuit goes in one side of the fixture and out the other.

Is it OK to also run another circuit through the fluorescent fixture in this manner? I'm basically using the fixture as conduit between two locations.

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This is fine as long as they can be joined end-to-end, are identified for through-wiring, or are listed and marked as a raceway, as per NEC 410.64. Just keep in mind that end-to-end joinable luminaires are limited to one branch circuit (that must feed one or more luminaire(s) in the set) in addition to the circuit that is feeding the remaining luminaire(s).

410.64 Luminaires as Raceways. Luminaires shall not be used as a raceway for circuit conductors unless they comply with 410.64(A), (B), or (C).

(A) Listed. Luminaires listed and marked for use as a raceway shall be permitted to be used as a raceway.

(B) Through-Wiring. Luminaires identified for through-wiring, as permitted by 410.21, shall be permitted to be used as a raceway.

(C) Luminaires Connected Together. Luminaires designed for end-to-end connection to form a continuous assembly, or luminaires connected together by recognized wiring methods, shall be permitted to contain the conductors of a 2-wire branch circuit, or one multiwire branch circuit, supplying the connected luminaires and shall not be required to be listed as a raceway. One additional 2-wire branch circuit separately supplying one or more of the connected luminaires shall also be permitted.

Also, in your case, as per 410.21, the luminaire must be identified for through-wiring in its integral junction box:

Branch-circuit wiring, other than 2-wire or multiwire branch circuits supplying power to luminaires connected together, shall not be passed through an outlet box that is an integral part of a luminaire unless the luminaire is identified for through-wiring.

  • Excellent! That's exactly the info I was looking for. Thanks! – watkipet Apr 14 '15 at 14:33
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Yes, that should be perfectly fine - most fluorescent fixtures are built with an application like this in mind (where many can be joined end-to-end - not all of which will be on the same circuit in many cases.)

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