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I use NM staples to secure NM cable to wood studs but I am unfamiliar with the options to secure NM cable directly to metal studs despite trying a number of different search terms. Would it be okay to substitute metal screws in place of the nails using plastic NM staples which come with nails or would that void the UL listing of the staples? Or, is there another recommended method? I know for horizontal runs I can go through the center of the stud (also, I believe that counts as supporting, but not securing as per NEC:2011 section 334.30). Also, for this case I need to secure and support a vertical run down from the ceiling to an electrical box.

The Preferred Solution will:

  1. secure the wire to the edge of the metal stud. The back edge of the stud faces the cinderblock foundation of my house and there is an air gap between the stud and the foundation wall.

  2. not involve wood or other organic materials since the wall is in a basement and I am trying to avoid materials that could potentially breed mold (moisture is currently well under control, but you never know what the future holds). E.g. Attach wood to the stud and then use NM staples to secure to the wood.

Code Reference:

334.30 Securing and Supporting.

Nonmetallic-sheathed cable shall be supported and secured by staples, cable ties, straps, hangers, or similar fittings designed and installed so as not to damage the cable, at intervals not exceeding 1.4 m (41⁄2 ft) and within 300 mm (12 in.) of every outlet box, junction box, cabinet, or fitting. Flat cables shall not be stapled on edge. Sections of cable protected from physical damage by raceway shall not be required to be secured within the raceway.

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Cables do need to be secured, but as you surmise, stapes and other nailed retainers wont work. There is a discussion of how to attach cables to steel studs in a brochure put out by the Steel Framing Alliance. Included in that broader pamphlet is this advice:

NM wire is not stapled to a CFS stud because the staples will not penetrate the steel. Instead, wires are held in place with wire ties fed through punchouts in the CFS or with mounted head cable ties which are cinched around wire bundles. Mounting hole or mounted head cable ties are specialized ties that have a ring at one end that serves for fastening the tie to a CFS component with a screw. Other specialized wire accessories are available to re-support wires, like cable supports and standoffs.

Cable fasteners such as these can be used

cable fastener

There are also a wide variety of cable ties that can be threaded through slots in the framing or have standoffs that can be screwed to the framing such asthis type

cable tie

Search steel stud cable mount and steel stud cable tie. Big box stores tend not to have them, so you probably need to seek out a specialty shop or look online.

You also can use cable spacers that work on wood or metal studs (using a screw)

cable spacer

It is also extremely important that you use grommets when you feed NM cables through steel studs or you risk a serious chance of shorting them out.

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According to bib you can use those yellow things, no idea what they are. If you can get the "Steel Framing Alliance" to wire your house for you, no doubt you will find out.

What the (hack) electricians who use Romex actually do in reality is usually not to secure it to anything. If they think they might get inspected by a non-bribed inspector, then what they do is wrap it to the stud using electrical tape at the minimum required distance. Once in while you can find an electrician who uses plastic cable ties. Its actually faster to use the plastic cable ties, but most electricians who are doing Romex jobs never get to the point where they need to secure anything, so they never bother to buy the ties even though its costs like $10 for 500 of them.

Galvanized stud is mostly used in commercial construction and commercial electricians always use metallic cable (or conduit).

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