Provided I use a box large enough to meet the fill requirements (and use 10 AWG conductors), are there any additional requirements I should be aware of when installing a new 240v 30 amp receptacle for a clothes dryer?

More specifically, does the box need to be metal or have certain attributes that a standard blue plastic box might not have? Is a cable clamp required?

My state (CA) currently adopts the 2011 edition of the NEC. I haven't had much luck finding anything that specifically addresses this so far.

1 Answer 1


Be sure you use a 30A double-pole breaker to adequately protect your wiring. Make sure you provide an equipment ground and use a NEMA 14-30 receptacle.

The box can be metal or plastic. Some form of cable clamp is always required, it's just that most plastic boxes have an integrated clamp (that finger-trap style door).

If using NM cable, The cable must be supported and secured by staples, cable ties, straps, hangers, or similar fittings designed and installed so as not to damage the cable, within 300 mm (12 in.) of the outlet box. If the wire is being fished through a finished wall and the wire cannot be secured in such a manner, this rule does not apply.

Pure Opinion

As far as selecting an actual box, from experience, I recommend getting a 2-gang plastic box (or something equivalent in size if you want to use metal). The larger the capacity the better because a NEMA 14-30 receptacle with four #10 wires is not only bulky, but can be a very stiff pain to manipulate. They even make boxes that are "specially" designed for this purpose.

If you use a 2-gang box, you'll want to get a faceplate that is designed to match (faceplates for NEMA 14-30 receptacles are also manufactured for 1-gang boxes).

  • I know they're standard these days, but I'd be really hesitant to use a plastic box for a 240v receptacle. But I hate plastic boxes in general. I second the suggestion of using a double-gang.
    – friedo
    Commented Jul 20, 2015 at 18:53
  • @friedo this can turn into quite a debate, but ultimately it's preference. There is nothing inherently wrong with using a plastic box.
    – mjohns
    Commented Jul 20, 2015 at 18:58
  • Obviously, NM (Romex®) is required to be secured if ran through unfinished spaces, otherwise it is permitted not to be secured. It is also okay to run through EMT as an extra protection in an unfinished wall of a garage, in which case a metal box is better.
    – Kris
    Commented Jul 20, 2015 at 20:59
  • @Kris good to bring up the securing-exception for running NM through finished spaces. Added that caveat to my answer.
    – mjohns
    Commented Jul 20, 2015 at 22:35

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