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I am trying to add a light fixture to a room. I have access to the studs in the wall (new wall being added to the room), but the ceiling is drywalled. There is no attic access. Unfortunately, the ceiling is hung from sound isolation bars, which means there are drywall screws poking up into the cavity between the floor joists. Since I am fishing a wire in this space, it was recommended that I use MC-type wiring to protect the wire from snagging on a screw.

This leads to my problem- I need to install an "old work" style ceiling box, but due to the MC wiring and need to bond the metallic sheath, I need to use a metal ceiling box. How is this typically done? I have been unable to find anything in metal similar to those plastic old work boxes with the tabs that flip out.

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    Do you need an in-ceiling box? Metal surface mount pancake boxes are easy to find and install and may work depending on your desired fixture. – Shimon Rura Mar 26 '13 at 13:30
  • I am planning on installing a 4' florescent fixture that needs to be flush with the ceiling, so unfortunately I think the box needs to be recessed into the ceiling. – MarkD Mar 26 '13 at 14:29
  • The reason for the old work box to be metal is so that with a pair of linesman's pliers, you can place the box against the drywall and bang it into place. A plastic box will break before it gets half-way through. – Some Guy Mar 19 '15 at 0:29
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Look for a "fan" box. they have telescoping arms that expand to secure the box between the ceiling joists. they are designed to hold the weight of a fan, but work well for any heavy fixture.

If your fixture is very light, say under a couple of pounds, simply use a standard metal box with MC clamps and surface ears, and install "hold-it's" on the sides of the box and behind the sheetrock. See http://meproducts.net/products?subcategory=C42 maybe one of my computer literate buds and find a better pic for you.

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    Thanks Shirlock. I found a telescoping fan box at HD (now that I knew what to look for) this evening, and it worked great! – MarkD Mar 27 '13 at 4:43
  • For the second part of your answer, my understanding is that the box has to be listed for lighting fixture support (50 lbs of lighting fixture support implicitly) or be explicitly marked on the box per 314.27(A)(2). How do "hold-its" applied to an old work metal box change the listing of the box to allow supporting a luminaire? – statueuphemism Oct 26 '16 at 14:53
  • 2014 NEC reference: 314.27 Outlet Boxes; (A) Boxes at Luminaire or Lampholder Outlets; (2) Ceiling Outlets. At every outlet used exclusively for lighting, the box shall be designed or installed so that a luminaire or lampholder may be attached. Boxes shall be required to support a luminaire weighing a minimum of 23 kg (50 lb). A luminaire that weighs more than 23 kg (50 lb) shall be supported independently of the outlet box, unless the outlet box is listed and marked on the interior of the box to indicate the maximum weight the box shall be permitted to support. – statueuphemism Oct 26 '16 at 14:53
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If you have some flexibility with where the box goes, you can mount a metal box directly to a joist. Otherwise you might need to open up a small part of the ceiling in order to install bracing between joists and then secure the metal box to the bracing. For hanging ceiling fixtures, I'd suggest you install the box to something fixed and not rely on a box with tabs as the drywall ends up bearing all of the weight.

Spend the little bit of extra time to do it right and you'll save yourself some headaches in the future. Repairing drywall is easy. Falling fixtures are messy.

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