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Article 406 Receptacles

Mike Holt for EC&M Magazine

Are you plugged in to what you need to know about Article 406?

True or false: The NEC requires receptacles to be mounted with the neutral slot on the left. Do you know what Article 406 says about this? Keep both answers in mind, as we look closer at Article 406 requirements.

Article 406 covers the rating, type, and installation of receptacles, cord connectors, and attachment plugs (cord caps). One important requirement of Article 406 is that you must ground (bond) the grounding terminal of a receptacle to a low-impedance fault current path [250.146, 250.148, and 406.3(C)]. You don't need to do this, however, if you are replacing a receptacle-and you comply with the applicable portions of 406.3(D).

The NEC specifies what that low-impedance path is, by requiring you connect the receptacle grounding terminal to the branch-circuit equipment grounding conductor [250.146] (Figure 406-4). If you install an isolated ground receptacle, though, follow the requirements of 250.146(D) (Figure 406-5).

Note: Figures are not contained in this newsletter.

Receptacle replacement requirements

If you have a grounding means in the enclosure, use a grounding-type receptacle-even if you are replacing a nongrounding-type receptacle [4-6.3(C)]. Make sure you ground (bond) the grounding terminal of that receptacle.

If the enclosure doesn't have a grounding means-for example, if the box contains old 2-wire NM cable without a ground-you can use a nongrounding type receptacle (Figure 406-6). You have two other options, as well. You can use a GFCI receptacle if you make sure it's marked "No Equipment Ground." Or, you can use a grounding-type receptacle-if it's GFCI protected and marked "GFCI Protected" and "No Equipment Ground."

When you replace a receptacle in a location where GFCI protection is required, the replacement must be GFCI-protected. See 210.8 for GFCI protection requirements.

Here's a pop quiz. A relative asks you to replace a failed GFCI receptacle. But, you notice the home has a two-wire system-no ground wire. Will that GFCI provide ground fault protection?

Answer: Yes. GFCI protection functions properly on a 2-wire circuit without an equipment grounding conductor. The equipment grounding conductor serves no purpose in the operation of the GFCI protection device. The GFCI uses a small CT on the neutral and a small CT on the hot. There is no CT on the ground. Buy a new GFCI, and you will probably find this information in the enclosed instructions.

Does this mean that if you extend a circuit from an ungrounded box you can install a GFCI? No. Permission to replace nongrounding type receptacles with GFCI-protected grounding type receptacles does not apply to new outlets that extend from an existing ungrounded outlet box. Once you add a receptacle outlet (branch-circuit extension), the receptacle must be of the grounding type and be grounded per 250.130(C) (Figure 406-8).

This requirement may seem inconsistent, but it's not. Here's the logic. Your existing two-wire system was installed per the Code that existed at the time. Today's NEC does not mandate ripping out existing two-wire systems and replacing them just so you can add a GFCI. Nor does it allow you to add on to the two-wire system and just throw in a GFCI. A three-wire system is safer than a two-wire system. So, if you add to an existing system, what you add must be of the three-wire configuration-not the two-wire configuration.


Have you ever wondered if you can mount a receptacle in, say, a hobby box you just happen to have lying around? Or in a cutout in the side of a panel where there's plenty of room and the receptacle is obviously protected? You can stop wondering-you can mount a receptacle only in a box designed for the purpose [406.4]. Fasten that box securely in place [314.23].

If you mount a receptacle in a box that is set back from the wall surface, install it so the mounting yoke of the receptacle is held rigidly to the wall surface. If the receptacle sits back too far, break off the "ears" on the yoke and use them as shim washers on the receptacle mounting screws.

In walls or ceilings of noncombustible material, boxes cannot be set back more than 1/4 in. from the finished surface. In walls or ceilings of combustible material, boxes must be flush with the finished surface [314.20]. You cannot have gaps greater than 1/8 in. at the edge of the box [314.21].

If you mount a receptacle in a box that is flush, install it so the mounting yoke of the receptacle is held rigidly against the box or raised box cover. If the receptacle mounts to the cover, it must be held rigidly to the cover with two screws (Figure 406-9).

Receptacle faceplates must completely cover the outlet opening and seat firmly against the mounting surface (406.5). Ensure a metal faceplate, if used, is grounded (bonded) by securing it to the receptacle (Figure 406-11).

Receptacles in Damp or Wet Locations

You can install a receptacle next to, but not within, a bathtub or shower space (Figure 406-16). Receptacles must be at least 5 ft from spas or hot tubs [680.21(A)(1) and 680.43(A)(1)].

What kind of enclosure must you use for a receptacle installed outdoors under roofed open porches, canopies, marquees (and the like)-if it's not subjected to beating rain or water runoff? One that is weatherproof when the attachment plug cap is not inserted and receptacle covers are closed (Figure 406-13). Receptacles thus installed are considered to be in damp locations.

But, what if you think you have a wet location? Look up "location, wet" in Article 100 to see the definition. If your location meets this definition, 406.8(B) applies. All 15A and 20A, 125V and 250V receptacles installed outdoors in a wet location must be within an enclosure and cover that is weatherproof at all times-even when an attachment plug is inserted (Figure 406-14).

Any other receptacle in a wet location must comply with one of the two following rules:

  • If the equipment plugged into it is not attended while in use, the receptacle must have an enclosure that is weatherproof with the attachment plug cap inserted or removed.
  • If the equipment plugged into it is attended while in use, the receptacle must have an enclosure that is weatherproof when the attachment plug is removed.

Suppose you flush-mount an outlet box on a wall surface in a wet location. In such a case, you must make the enclosure weatherproof by using a weatherproof faceplate assembly that provides a watertight connection between the plate and the wall surface.

Overlooked requirements

Our familiarity with receptacles can cause us to overlook certain requirements. For example, what kind of receptacle you can use with aluminum wire, and how you can wire it? First, look for the marking CO/AL on the terminal screws. These markings are required for all receptacles rated 20A or less and designed for direct connection with aluminum conductors. If the receptacle is over 20A, see the manufacturer's instructions or contact the manufacturer to ensure you're not violating the UL listing for that receptacle.

Here's another fact regarding UL. Per UL requirements, aluminum conductors cannot terminate onto screwless (push-in) terminals of a receptacle. More than one installation has been rejected for this….

Suppose you wire a receptacle for isolated ground. Do you know how to identify the right kind of receptacle for such an application? It must have an orange triangle marking on its face [250.146(D)] (Figure 406-1).

What else do people commonly overlook with isolated ground receptacles (IGRs)?

  • You can use IGRs only with an insulated grounding conductor installed with the circuit conductors.
  • If you install an IGR in a nonmetallic box, you must cover it with a nonmetallic faceplate-because you can't ground (bond) the metal faceplate in such an installation (Figure 406-2).

Now, what about our two opening questions? The answer to both is the NEC doesn't specify which way to orient a receptacle. The ground terminal can be up, down, or to the side. In the last few Code cycles, proposals to specify the mounting orientation were all rejected.

Well, there is one exception to this non-specification. If you install a receptacle in a countertop or similar work surface in a dwelling unit, you cannot install it in a face-up position (Figure 406-10).

We have focused on the receptacle aspect of Article 406. But, this Article covers more. Some of the provisions in Article 406 surprise people who thought receptacle requirements are too "simple" to worry about. Were you able to answer our two opening questions correctly, and pass the pop quiz? Were you aware of all the requirements we identified as "commonly overlooked?" If so, you still might find a surprise or two in Article 406. That's a good reason to become familiar with it now, rather than at inspection time. You'd hate to be dinged on something as "simple" as a receptacle requirement, wouldn't you?

The above was extracted from Mike Holt's best selling book "Understanding the National Electrical Code."

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