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I purchased several LED flat panel fixtures that came without wiring instructions.

I’m using suspension cable kits to hang the lamps from an open basement ceiling with fiberglass insulation and TJI-type joists.

The lamps have Junction Boxes (pictured) with what look like type NM (romex) inputs — to the LED driver — and tiny, maybe 18-20 gauge lines to the LEDs themselves.

The fixtures draw a rated 40 watts. I have a junction box in the ceiling currently with a bare bulb fixture.

Is it necessary or required by NEC to use type NM-B/Romex to wire these fixtures? It doesn’t seem very useful to use solid NM rather than stranded lamp cord, since I’ve seen simple lamp cord provide power safely to 150-watt floor lamp bulbs all my life.

Junction box on LED fixture photo

bare bulb in junction box photo

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    What's the issue with using NM here? Handling?
    – ThreePhaseEel
    Commented Apr 28, 2019 at 21:05
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    Would you be open to other wiring methods?
    – ThreePhaseEel
    Commented Apr 28, 2019 at 23:07
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    Do you want to be able to dim them in the future? Also, is leaving a bit of extra cable up in the ceiling for future positioning an issue for you?
    – ThreePhaseEel
    Commented Apr 29, 2019 at 1:38
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    The weird label instructions mean "don't short the LED outputs to the dim inputs" basically, AFAICT
    – ThreePhaseEel
    Commented Apr 29, 2019 at 1:42
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    Do you have access to an electrical supply house that can order things in for you?
    – ThreePhaseEel
    Commented Apr 29, 2019 at 1:53

1 Answer 1

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I gather that you're hanging the lights from cables or chains, and as such, it's possible for them to move or swing. As such, you must use cordage for the connection from light to fixed ceiling box.

Cordage is - well, it's the type of electrical wiring you've been handling all your life. Almost every appliance has a cord. It's designed to flex. It also costs a little more. It's not allowed as permanent wiring, except for a certain few exceptions.

Use of cordage to luminaires in open spaces is explicitly allowed by NEC 400.7 (now 400.10), and I make full use of it. Further, nothing says you can't make them cord-and-plug-connected. They make cover plates that take receptacles, for 4" (across the corners) octagon boxes.

enter image description here

Don't let price tempt you into using a 2-prong cord. The cable/chain hangers are NOT grounds. For 3-prong cords-with-plug, my favorite is Target's $5 8' extension cord, lop off the socket end and you're all set. It's stiff, though; McMaster-Carr has more flexible ones cheap, but the shipping! If you're hardwiring both ends, your local electrical supply will have a variety of cordage, use at least 16 AWG.

However, cordage is not allowed above a drop ceiling or in any kind of plenum space: NEC 400.7 (now 400.12). In that case you need to use one of the Chapter 3 wiring methods, typically a flexible metal conduit or prefabricated wire whip.

Lastly, ballast disconnects. Code requires any hardwired luminaire to connect via disconnect plugs. LEDs might be exempt because they're not technically fluorescents. However, the principle is the same: the power supply/ballast is likely to fail at some point, and you need a way to de-energize with certainty. Since you have to make a connection betweeen house wiring and driver anyway, make it through one of these. These cost less than $1 each.

enter image description here enter image description here

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    Another great source of flexible cordage w/ plug is IEC cables -- since every computer and monitor needs one, they're even more of a cheap commodity. monoprice.com/product?p_id=5279
    – Nate S.
    Commented Apr 29, 2019 at 15:57
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    At 40w or ..33 amps I would the smallest cord I could find if plugging them in but if hard wiring then it gets a bit more complicated since the entire assembly is not ul listed.
    – Ed Beal
    Commented Apr 29, 2019 at 18:27
  • Great info here. I believe my units in the picture above have an equivalent quick-disconnect (pushbutton to release the wiring.). Now I know why. Do I maintain UL rating and code-compliance if I hardwire all four or six fixtures in the room, using IEC type cordage, with plug-ends cut off, from the fixture’s junction box, all the way to a wire-nut in the ceiling junction box? I assume each fixture needs its own “home run” to a junction box. It sounds like from your answer I do, not sure from @EdBeal ‘s comment as to whether this wiring would be considered “permanent” or not.
    – whiskeychief
    Commented Apr 29, 2019 at 19:13
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    If you're snipping off both socket and plug (or even if you're retaining the plug) the labeling on the side of the cord is what decides whether it's legal. It must be a legal type for cordage, e.g. SJOOW, SJTW, etc. I wouldn't trust cheapie mail-order IEC cables unless I actually read the numbers off the side of the cord. But yes, you go in a strain relief or cable clamp into the junction box, and wirenut to in-wall wiring there.
    – Harper - Reinstate Monica
    Commented Apr 29, 2019 at 19:37
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    @whiskeychief as a matter of fact, there is no limit. I have a 40' one. I would use 2 hooks faced opposite directions not a staple. Cordage isn't made to be crimped like Romex. (Well that isn't either).
    – Harper - Reinstate Monica
    Commented May 3, 2019 at 14:06

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