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Are electrical boxes required by code to house electrical devices and outlets or is it just an accepted way of doing it?

If it is required, where does this requirement come from? Would it still hold up if an outlet receptacle had no exposed metal parts (and accepted wiring with push-in terminals)?

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Electrical boxes are required by code for some wiring methods. 300.15 specifically mentions conduit, tubing, Types AC, MC, MI, nonmetallic sheathed cable, and other cables. However, 300.15(H) says that insulated devices do not require a box, as permitted by 334.40(B).

300.15(H) Insulated Devices. As permitted in 334.40(B), a box or conduit body shall not be required for insulated devices supplied by nonmetallic-sheathed cable

334.40(B) Devices of Insulating Material. Self-contained switches, self-contained receptacles, and nonmetallic-sheathed cable interconnector devices of insulating material that are listed shall be permitted to be used without boxes in exposed cable wiring and for repair wiring in existing buildings where the cable is concealed. Openings in such devices shall form a close fit around the outer covering of the cable, and the device shall fully enclose the part of the cable from which any part of the covering has been re-moved. Where connections to conductors are by binding-screw terminals, there shall be available as many terminals as conductors.

There's also 300.15(E), which allows devices with an enclosure integrated into the device.

(E) Integral Enclosure. A wiring device with integral enclosure identified for the use, having brackets to securely fasten the device to walls or ceilings of conventional on-site frame construction, for use with nonmetallic-sheathed cable, shall be permitted in lieu of a box or conduit body.

So, yes. If a receptacle was designed and listed specifically to be used without a box, then it can be used without a box.

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    But everything generally used is listed; that alone does not qualify it to be used without a box. You mean it must be designed and listed specifically to be used without a box. May 26, 2017 at 1:54
  • @Harper Do you know the listing number for that type of a device?
    – andrey
    May 26, 2017 at 2:07
  • Also relevant are self contained surface mounted light kits that just require a NM connector, and no electrical box, e.g., some fluorescents and sconces.
    – Kris
    May 26, 2017 at 2:21
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    @Kris yes, that's in another section of 300.15. I only specifically talked about 300.15(H), because that's what OP mentioned in the question.
    – Tester101
    May 26, 2017 at 2:54
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    No. This is an FAQ around here: "This random component I found in Mouser/Digi-Key/Sparkfun/McMaster/Grainger is UL approved. Can I use it in my house wiring?" Nope, because it's not listed to be used as part of house wiring. It is only approved to be a component in a machine which is subsequently listed. Maytag can use it in a dryer; you can't use it in your house. May 26, 2017 at 4:56
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The governing rules are in Article 110.

Approved. Acceptable to the authority having jurisdiction. [your town electrical inspector].

Equipment. A general term, including fittings, devices, appliances, luminaires, apparatus, machinery, and the like used as a part of, or in connection with, an electrical installation.

Identified (as applied to equipment). Recognizable as suitable for the specific purpose, function, use, environment, application, and so forth, where described in a particular Code requirement.

Listed. Equipment, materials, or services included in a list published by an organization that is acceptable to the authority having jurisdiction and concerned with evaluation of products or services, that maintains periodic inspection of production of listed equipment or materials or periodic evaluation of services, and whose listing states that either the equipment, material, or service meets appropriate designated standards or has been tested and found suitable for a specified purpose.

110.2 Approval. The conductors and equipment required or permitted by this Code shall be acceptable only if approved.

110.3 Examination, Identification, Installation, and Use of Equipment.

(A) Examination. In judging equipment, considerations such as the following shall be evaluated: (long list deleted)

(B) Installation and Use. Listed or labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling.

So that's it. You can't use equipment that isn't approved. And "Approved" means by your city electrical inspector, not UL. The inspector will defer to UL and generally approve appliances which are listed, provided you use them consistent with their instructions.

We get this question all the time. "I'm an electronics guy and I buy a lot from Digi-Key, Mouser, McMaster, Grainger etc. They have components that are UL approved. Can I stick them in my house wiring?" And the answer is always "nope". The UL approval on components means that UL will accept them as part of an appliance they are listing. You can't use the components directly; in fact, their listing, labeling and instructions do not discuss using them directly as equipment for house wiring. And as discussed in NEC 110.3B, you cannot install them except in accordance with the instructions.

And usually people try to argue with us. Bottom line it's not our call, it's the inspector's. If it isn't conventionally used for houses, the city inspector won't allow it, and that's the end of the subject.

If you want a good guideline of what is conventionally used for houses, go to a real electrical supply house. (Home Depot etc. are weak substitutes). If you can use it, they'll have it on their sheves. For instance don't use this relay, use this relay. Ask the staff, they'll tell you what can do and how best to do it.

You do know you need to pull a permit for any electrical work that involves new components. The inspector will need to know what you plan to do, and she will inspect. If anything is not right, she'll make you tear it out and do it properly. If she thinks you're a total hack, she'll force you to hire an electrician to finish the job.

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    That's why you need the UL Whitebook, it actually points to NEC code sections.
    – Tester101
    May 26, 2017 at 10:33
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    Good answers but I don't like the question. It's what I think is a leading question and I suspect I know where it is leading. Which Is " Can I put a receptacle in the wall without installing a box if I use the "pushin" connections in the back." and the answer is no. In fact every good electrician wishes they would take those damn things off the back of the receptacles. May 26, 2017 at 13:28
  • @RetiredMasterElectrician Right, that what my question was really about. As I understand, the reason why push-in receptacles aren't certifiable as self-contained is that they don't have wire clamping? What's the reason self-contained aren't used outside of RVs and boats?
    – andrey
    May 26, 2017 at 19:11
  • @andreyg - I really don't comment on RV's and boats. For an electrician the our wiring stops at the dock or rv pedestal. Think of rv's and boats as large pieces of self contained equipment. Their designs are covered by an entirely different set of codes and design standards and should be dealt with by their own set of specialists. May 28, 2017 at 13:55
  • @andreyg the receptacle isn't certified as self-contained because the manufacturer did bot seek that certification and therefore did not alter the product to meet it. I think you may be barking up the wrong tree because you do not understand how jurisdiction flows. Code-lawyering doesn't work. For instance if your goal is to develop a mass producible tiny house anyone can plop on their land, perhaps you are missing that the AHJ in each town will inspect and can reject the electrical setup. Trying to code-lawyer a Peoria county inspector from your L.A. office will fail miserably. May 28, 2017 at 14:33

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