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By Mike Holt, for EC&M Magazine
Don't let your familiarity with switches interfere with NEC compliance.
We've been around switches all of our lives. We even have them throughout our homes. They are so familiar to us, we can easily think we know all about installing them.
But, the NEC devotes an entire article (404) to switches. Article 100 provides six separate definitions for "switch," covering bypass isolation, general-use, general-use snap, isolating, motor-circuit, and transfer. Article 404 requirements apply to all switches, switching devices, and circuit breakers used as switches.
Some like it hot
You wire a switch 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)] (Figure 404-2).
Note: Graphics are not included in this newsletter.
Thus, for a simple on/off operation of a 120V light, you wire the switch contacts in series with the hot lead. That is, the hot lead comes from the supply to the switch, and then goes from the switch to the light. The neutral and ground wires are not switched, though 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 are still switching only the ungrounded (hot) conductor [404.2] (Figure 404-1).
In applications where you are pulling wires from spools into raceway, your black wire is hot, neutral is white (or gray), and green or bare is ground. You could use some other color for the switched hot, if you desired. But, what if you are 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 are 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 is 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)].
Now that we've addressed the hot wire, what about switch installation requirements? You need to consider such issues as:
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) is not more than 6 ft 7 in. above the floor or working platform [404.8] (Figure 404-8).
You can mount switches (and circuit breakers used as switches) higher than 6 ft 7 in., if they are next to the equipment they supply and are accessible by portable means (Figure 404-10). There is no minimum height requirement for switches.
You cannot group or gang snap switches in enclosures with other snap switches, receptacles, or similar devices if the voltage between devices exceeds 300V (Figure 404-11 and Figure 404-12).
Switch boxes and faceplates
There cannot be any gaps greater than 1/8 in. at the edge of the box [314.21] containing the switch. 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:
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. On each end of the yoke are 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 are mounting the switch flush to the wall, it must be seated against the finished wall surface [404.10]. The means of accomplishing this is obvious-hold the switch up and screw it in.
If you are 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 that 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-this 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 will see a "score-line"
marking 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.
Notice, these ears provide a small adjustment-they don't correct for gross mismounting. In walls or ceilings of noncombustible material, boxes cannot be set back more than 1/4 in. from the finished surface. In combustible walls or ceilings, boxes must be flush with the finished surface [314.20].
You must ensure switches-including dimmer and similar control switches-are effectively grounded to an effective ground-fault current path. Provide a means to ground metal faceplates, whether or not you are installing a metal faceplate (Figure 404-13)-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)] if:
Exception: 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. That's exactly the reason you should periodically review Article 404. If you make sure the various things you know from Article 404 don't end up in the "off" position, your switch installations will comply with NEC requirements.
Note: The above was extracted from my best selling book, Understanding the National Electrical Code.
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