National Electrical Code Top Ten Tips: Article 404 -- Switches
by Mark Lamendola
Based on the 2020 NEC
Please note, we do quote from copyrighted material. While the NFPA
does allow such quotes, it does so only for the purposes of education
regarding the National Electrical Code. This article is not a substitute
for the NEC.
These are the 10 NEC Article 404 items we deem most important, based
on the pervasiveness of confusion and the potential costs of same.
- Donít dismiss switches as not deserving your
attention. There's a reason why the NEC has finally devoted an entire
Article to them. Even the trade magazines, such as EC&M, are writing about
- You must wire switches such that you are switching only the ungrounded
(hot) conductor [404.2(B)]. Don't switch the neutral or the ground. Also, take care to connect these to the correct terminals.
Terminals are usually color-coded. If they aren't then on a given project always connect the switches the same way. For example, on all two-way switches for 120V systems you decide the connect the hot lead to the top terminal and the load lead to the bottom terminal. If you have lighted switches, these usually need a ground so allow for that when running the conductors. If wiring three-way switch circuits, do the next electrician a favor and use some convention to mark the hot wire. For example, use a label maker to create a HOT tag and affix it to that wire. Do not piggytail neutral wires to GFCIs; for the device to provide downstream protection it must be in series with neutral.
- Put switches in enclosures listed for such a use [404.3(A)]. Putting a switch in an
enclosure that is not listed for use as a switch enclosure puts you at risk
for liability, and puts the switch users at risk of injury to property and
people. When deciding on a switch enclosure, it's often worthwhile to go with one that is a little larger so there is sufficient room to make the necessary connections. It is a common practice on 120V circuits, especially residential ones, to exceed the conductor limit on a solderless connector because the box is too small to make the connections correctly without really jamming things into the box to make them fit.
- Don't run other wiring through switch enclosures [404.3(B)]. These enclosures have
one purpose: to act as switch enclosures. They are not pullboxes, junction
boxes, or raceways. This violation occurs in residential circuits, and it is also done in commercial and industrial circuits. Among the reasons not to do it, such an arrangment complicates the job of replacing the switch.
- If you put a switch in a wet location, use an enclosure rated for wet
locations [404.04]. Don't use a GFCI as a license to violate this rule. A GFCI is not
intended to overcome all problems that may arise from putting a switch in an
enclosure not rated for the intended use. Among other problems, a GFCI cannot protect itself from corrosion; that's what an enclosure rated for wet locations is for.
- Mount switches such that gravity won't close them [404.6]. That means "OFF" is
down and "ON" is up. What about mounting it sideways? That may violate its testing lab certification and may also result in premature mechanical failure. If you want a switch to operate with a side to side motion, then install a switch designed for that. If the switch is a disconnecting means for a load with a decent amount of energy (e.g., an industrial motor), mount the switch such that the operator stands to one side of it while operating it with the left hand; this puts the operator out of the blast path.
- If you are grouping or ganging switches, arrange them so they are
operating at similar voltages [404.8]. The NEC requirement is that the voltage
differential not be more than 300V, unless you accommodate the difference by
placing such switches in their own enclosures.
- Faceplates must completely cover the opening in which a switch is mounted [404.9]. What if the opening is too big? Then install an adapter plate to make it smaller, or use a bigger faceplate, or replace the enclosure. Sometimes in DIY residential jobs, the homeowner cut a drywall hole without using a template or a jigsaw. The "fix" may involve adding some drywall compound or caulking to the edge of the drywall. A correct fix would be to cut all the way from stud to stud and to allow for a sufficiently tall (e.g., 2 feet) section of drywall in that space. Then use the proper tools and method to make a correct hole. Use self-adheive drywall mesh (not drywall tape) when repairing the joints this repair creates. You will have a mechanically solid patch that can be made perfectly smooth at the joints for painting.
- You can use general-use dimmer switches only for the control of
permanently installed incandescent luminaires, unless they are listed for
other loads and you install them per manufacturer's directions [404.14(E)]. If you use these with dimmable LEDs, they may seem to work just fine. At first. Then you get a callback that the switches are making funny noises and the lights flicker periodically.
- You must observe the wire-bending space requirements of 404.3 and Table
312.6(B) [404.28]. This does not mean you bend the wires to those dimensions one you are done with the job. It means you adhere to those dimensions at all times. Once you exceed the wire-bending radius (too narrow of a bend) for a conductor, the damage is done. Replace the conductor.