Just like the receptacle, which was covered in this column last month, switches are a common element in everyday life. You can find them at work, in public, and at home, so it's easy to think you know all about installing them.
But the NEC devotes an entire article (Art. 404) to them for good reason. Art. 100 provides six separate definitions for “switch,” covering bypass isolation, general-use, general-use snap, isolating, motor-circuit, and transfer. Art. 404 requirements apply to all switches, switching devices, and circuit breakers used as switches.
Some like it hot. Switches are wired to make or break the supply conductor — also called the hot lead. The NEC specifically bars switching the grounded (neutral) conductor or the grounding conductor [404.2(B)] (Fig. 1 at right).
Thus, for a simple on/off operation of a 120V light, the switch contacts must be wired in series with the hot lead. In other words, the hot lead comes from the supply to the switch, and then goes from the switch to the light. The neutral and ground wires aren't switched, but you must ground the switch body.
This same hot wire logic carries over to three-way and four-way switches. When you wire in such a configuration, you're still switching only the ungrounded (hot) conductor [404.2(A)] (Fig. 2 at right).
In applications where you're pulling wires from spools into raceway, the black wire is hot, neutral is white (or gray), and the ground is green or bare. You could use some other color for the switched hot, if you desired. But what if you're using a three-wire cable?
Residential applications typically use nonmetallic-sheathed cable for all circuits. Industrial and commercial applications often use some type of metallic cable assembly for 120V power distribution — for example, when deploying pre-fab “snap-in” construction methods. If you're running a cable assembly, how do you wire for a switch? After all, you have only one black wire in that cable.
You can use the white or gray conductor within a cable assembly for single-pole, three-way or four-way switch loops if it's permanently re-identified to indicate its use as an ungrounded (hot) conductor at each location where the conductor is visible and accessible [200.7(C)(2)].
Installation issues. Now that we've addressed the hot wire, what about switch installation requirements? You need to consider the following issues:
Induction. Where metal raceway (or metal-clad cable) contains the conductors for switches, arrange the wiring to avoid inductively heating the surrounding metal. To accomplish this, run all conductors of a given circuit in the same raceway [300.3(B) and 300.20(A)]. Note the 404.2(A) exception, though: a grounded (neutral) conductor isn't required in the same raceway or cable with travelers or switch leg (switch loops) conductors.
Switch enclosures [404.3(B)]. Switch enclosures can contain splices and taps, and conductors can feed through them. But this is true only if the splices or taps don't fill the wiring space (at any cross section) to more than 75%, and the wiring (at any cross section) doesn't exceed 40% (312.8) (Fig. 3).
Wet locations (404.4). You can locate switches next to, but not within, a bathtub or shower space, unless the switch and its assembly have been listed for this purpose. You must locate switches at least 5 feet from pools [680.22(C)], outdoor spas and hot tubs [680.41], and indoor spas and hot tubs [680.43(C)]. This 5-foot rule doesn't apply to switches located adjacent to bathtubs, shower stalls, or hydromassage bathtubs (680.70 and 680.72).
Position. When the switch is operated vertically, observe the ON marking and install the switch so the “up” position means “on.” This provides a failsafe operation in the direction of gravity (240.81). Of course, three-way and four-way switches aren't marked ON or OFF, so this rule doesn't apply to them.
Accessibility and grouping. All switches (and circuit breakers used as switches) must be operable from a readily accessible location. Install them so the center of the operating handle grip (when in its highest position) isn't more than 6 feet 7 inches above the floor or working platform (404.8).
You can mount switches (and circuit breakers used as switches) higher than 6 feet 7 inches if they're next to the equipment they supply and are accessible by portable means [404.8(A) Ex. 2]. There is no minimum height requirement.
Federal American Disabilities Act (ADA) guidelines on switch mounting heights would supersede the NEC, which is still not “code” everywhere in any single form. The ADA is in effect in all parts of the United States, even if that area doesn't have an electrical code. In addition, various states have put out their version of the ADA that may actually be stricter than the federal guidelines. A state isn't allowed to make its rules more lenient than the federal guidelines.
You can't group or gang snap switches in enclosures with other snap switches, receptacles, or similar devices if the voltage between devices exceeds 300V (Fig. 4).
Switch boxes and faceplates. There can't be any gaps greater than 0.125 inch at the edge of the box that contains the switch (314.21). Drywall installers sometimes make this requirement difficult to comply with because they cut the hole too large or in an odd shape. To fix this, you may need to cut out a large section of drywall and replace it with one that has a properly sized hole. Use a receptacle template when making the new hole. To reduce the overall cost of the job, make sure the drywallers use a template for the original hole — even if you have to provide it to them.
Where flush-mounted, the faceplate must seat against the wall surface (404.9). The key to compliance is correctly mounting the switch to the box. You have two options for mounting a switch:
Mount it flush to the wall when the box is set back from the wall.
Mount it flush to the box when the box is mounted flush to the wall.
To mount the switch correctly, you need to know a bit about the switch mounting parts. The “yoke” is the entire metal piece that holds the switch body. Each end of the yoke has tabs with holes in them; manufacturers call these “mouse ears.” You may need to use these ears to adjust the depth of the switch relative to the wall or the box.
If you're mounting the switch flush to the wall, it must be seated against the finished wall surface (404.10). The means for accomplishing this are obvious; hold the switch up and screw it in.
If you're mounting the switch to the box, proper mounting isn't so obvious. You may encounter some error in how far back the box is from the wall surface — especially with wooden studs involved. The box has a guide mark on it, but many things can cause a need for adjustment at the switch.
Suppose the box is set back too far. How do you line things up, depth-wise? Don't try to seat the faceplate flush against the wall by over-tightening the mounting screw because it can damage the faceplate. And leaving the switch mounting screws loose to facilitate this is unsafe.
Instead, use the mounting adjustment ability of the switch itself. If you look at the yoke, you'll see a “score-line” that marks the beginning of each ear. Using a pair of flat-edged pliers, snap the ears off the yoke. Then, use the ears as washers to space the yoke out away from the mounting box. That is the approved method.
Some people leave the ears on and just bend them back to gain the proper spacing. While this works and will allow you to “dial in” the correct spacing, it isn't a recommended method. First of all, those ears aren't made to be bent back. Using them in that manner can lead to a mechanical failure, not to mention the fact that the method is time-consuming. The degree of adjustment is greater with bending than with shimming, but it's not necessary.
Note that these ears provide a small adjustment; they don't correct for gross mismounting. In walls or ceilings of noncombustible material, boxes can't be set back more than 0.25 in. from the finished surface. In combustible walls or ceilings, boxes must be flush with the finished surface (314.20).
Grounding. You must ensure switches, including dimmer and similar control switches, are effectively grounded to an effective ground-fault current path [404.9(B)]. Provide a means to ground metal faceplates, whether or not you're installing a metal faceplate (Fig. 5). Someone else may install a metal faceplate later. A switch is considered effectively grounded to an effective ground-fault current path [250.4(A)(3)] in either of these cases:
It's mounted with metal screws to a metal box (or to a nonmetallic box with integral means for grounding devices).
An equipment grounding conductor or equipment bonding jumper is connected to an equipment grounding termination of the switch (404.12).
However, you can replace an existing snap switch that's installed where no grounding (bonding) means exist in the outlet box, without grounding (bonding) the switch yoke if you use a nonmetallic faceplate.
It may seem you know all the requirements for switches because you work with them all the time, but that's exactly the reason you should periodically review Art. 404. If you make sure the various things you know about their requirements don't end up in the “off” position, your switch installations will comply with NEC requirements.