If you have a problem related to the National Electrical Code (NEC), are experiencing difficulty in understanding a Code requirement, or are wondering why or if such a requirement exists, ask Charlie, and he will let the Code decide. Questions and comments can be sent to firstname.lastname@example.org. Answers are based on the 2011 NEC.
I’m looking for a requirement for three- and four-way switches located at each entrance to a room. Article 404 does not outline any such requirement. Where in the Code is it defined?
There are no specific requirements for three- and four-way switches where there are multiple entrances to a room or an area. Section 210.70 covers lighting outlets required and the applicable switching requirements. Section 210.70(A)(2)(c) has a requirement for interior stairways that requires a wall switch at each level that has an entry to the stairway. This can best be done using three- and four-way switches, but it is not a specific requirement.
Horizontals made plain
Can I install a load center horizontally?
It’s surprising how often this question comes up. If you install a load center in the horizontal position, the circuit breakers would operate in a vertical direction. The top row of circuit breakers would then be “on” in the down position. NEC 240.81 requires that, where circuit breaker handles are operated vertically, the “up” position of the handle shall be the “on” position. Therefore, you cannot install them horizontally.
I have been searching the Code book for information regarding the maximum distance between terminations before a pull box must be inserted for a three-wire 120/240V feeder circuit using 300 MCM aluminum wire. Can you help me locate this info?
The NEC does not specify a maximum distance that raceways can be run before a pull box must be used. Informational Note No. 1 in Chapter 9, Table 1, reads: “Table 1 is based on common conditions of proper cabling and alignment of conductors where the length of the pull and the number of bends are within reasonable limits. It should be recognized that, for certain conditions, a larger size conduit or a lesser conduit fill should be considered.” This note and 90.1(C), which reads, “This Code is not intended as a design specification or an instruction manual for untrained persons,” place the responsibility for proper design and installation on the installer.
AFCIs, legally speaking
In the 2008 NEC Section 210.12(B), it states arc-fault circuit interrupter (AFCI) protection must be provided for outlets in family rooms, dining rooms, or similar rooms or areas. In 210.52(C), it mentions kitchens, pantries, breakfast rooms, dining rooms and similar areas. Doesn’t that mean kitchens, pantries and breakfast rooms are all similar to dining rooms, and therefore, as mentioned in 210.12(B), AFCI protection would be required in all those locations? Since both sections are in Article 210, it would be reasonable to assume that what is in one section would apply to the similar areas. The same panel deals with both sections. Maybe I’m being more of an attorney than an electrician, but there are a lot of attorneys out there when it comes to interpreting the NEC. What is your opinion?
Don’t quit your day job. However, you make a good point. I think the term “similar areas,” although not defined, is used to discourage wordsmiths (nit-pickers and attorneys), but I believe the requirements are clear enough for qualified installers and inspection authorities.
I have a question regarding the use of two 2-conductor NM cables to form a three-way switch loop. I believe that this installation is not Code-compliant because it’s a violation of 300.3(B), which requires all conductors of a circuit to be contained within the same cable.
Read on. Section 300.3(B)(3) permits conductors with a nonmetallic sheath to be run in different cables. The reason for the general rule that all conductors of a circuit must be contained within the same raceway or cable is to cancel out the magnetic fields produced by the current flow in the conductors. Since there is no ferrous metal raceway or magnetic cable sheath on Type NM cable where current flow could be induced by the magnetic field, all of the circuit conductors of the same circuit are not required to be contained in the same cable.
In the bath
Section 406.9(C) states that no outlet shall be placed within or directly over a bathtub or shower stall. What is meant by “within”? Is this the four corners of the tub or the tub area? What is considered the tub area?
Actually, 406.9(C) states receptacles shall not be installed within or directly over a bathtub or a shower stall. Too often the term “outlet” is thought to mean receptacle only, but there are lighting outlets, which can be installed in these areas. Check out 410.10(D) for requirements for bathtub and shower areas, and if you have an NEC Handbook (which you should have), look at Exhibit 410.1 in the 2011 NEC Handbook.
Is it single?
In a recent response to a question regarding a refrigerator receptacle, you said it must be a single receptacle. I’m not quite sure how you interpret section 210.21(B)(1) to require a single receptacle. The section appears to simply state that if you have a single receptacle on a single circuit, the receptacle has to be rated for the amperage of that circuit. I don’t think the section requires a single receptacle if you are using a single circuit.
Exception No. 2 to 210.52(B)(1) permits the receptacle outlet for refrigeration equipment to be supplied from an individual branch circuit rated 15 amperes (A) or greater in lieu of being supplied from a small appliance circuit. If you choose this option, Article 100 defines an individual branch circuit as a “branch circuit that supplies only one utilization equipment.” The use of a receptacle device with more than a single receptacle would permit more than one utilization equipment to be supplied. NEC 210.21(B)(1) shows the requirements for a single receptacle on an individual branch circuit.
What can I use?
Can you use the 90° column when derating? I have four 4-inch underground conduits. I have an adjustable trip, 1,600A circuit breaker. I plan on using four sets of 600-kcmil conductors with a 100 percent neutral. I am told they have nonlinear loads (so we have to derate). Can we use the 90° column to derate the 600 kcmil from 475A to 380A (80 percent), then dial back the circuit breaker to 1,500A? Is this NEC legal?
Using the 90° column of Table 310.15(B)(16) (formerly Table 310.16) is permitted by 110.14(C) for ampacity adjustment (derating) of conductors. Ampacity adjustment is required by 310.15(B)(3) where the number of current-carrying conductors in a raceway exceeds three. Your installation has four 600 kcmil conductors in each raceway but only the three-phase conductors are considered as being current-carrying. Also, ampacity adjustment is not required. Using four 600 kcmil per phase (4 420) equals 1,680A and using a 1,600A breaker is permitted.
I am not sure I agree with your answer regarding the individual branch circuit for a microwave. In your October 2010 column, you wrote the 15 amp-rated circuit could not be used for the 12.3A-rated microwave. Section 210.23 allows an individual branch circuit for any load for which it is rated. The 12.3A microwave can be served by a 15A circuit with a single 15A receptacle. Your quote of 210.21(B)(2) is for two or more outlets; thus, it no longer meets the definition of an individual branch circuit. I also think the Code allows the 20-amp single receptacle on the 15 amp circuit per 210.21(B)(1). I agree that, if it were not an individual circuit, the rating must be 20A per Table 210.21(B)(2) and 210.23(A)(1).
Yes, thanks for your very knowledgeable correction. NEC 210.23 permits an individual branch circuit to supply any load for which it is rated. A 12.3A-rated microwave oven can be supplied by an individual 15-ampere circuit.
In your November 2010 column, you state a variable speed drive (VSD) “alters the speed by changing the voltage to the motor.” Then you state, “With a VSD, you have continuous control of the motor speed by varying the output frequency from the drive unit.” Direct current does not have a frequency, hence the need to vary the voltage to affect the speed of a motor. Was this an error?
I don’t see an error in my answer. A variable frequency drive (VFD) varies the speed of an AC motor by varying the frequency. A VSD varies the speed of a DC motor by varying the voltage. Since both the VFD and the VSD are used to vary motor speed, they are collectively called variable speed drives. Don’t make a big deal out of it.
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