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 can be sent to firstname.lastname@example.org. Answers are based on the 2011 NEC.
Why are some panelboards marked “Suitable Only For Use As Service Equipment” and others are marked “Suitable For Use As Service Equipment”?
Panelboards with the neutral bar factory--bonded to the frame or enclosure are marked “Suitable Only For Use As Service Equipment.” Panelboards incorporating provisions for bonding the neutral bar to the frame or enclosure in the field can be marked “Suitable For Use As Service Equipment.” This information can be found in the UL White Book under QEUY.
Clarifying conductor count
In your answer to “How much free conductor?” (Electrical Contractor, January 2012), you state that 314.16(B)(1) permits unbroken conductors passing through the box to be counted as one, and it doesn’t restrict the length. What about the line in that same section that reads, “Each loop or coil of unbroken conductor not less than twice the minimum length required for free conductors in 300.14 shall be counted twice”?
It means that, if you have an unbroken conductor that passes through the box and its length is such that cutting this conductor in the center would make the lengths of the conductors derived be as much as or more than is required for free conductors in 300.14, this conductor must be counted twice.
Multiwire circuits in office partitions
Why are multiwire circuits not permitted in office furnishing partitions?
The receptacles used in office partitions are likely to be used for office equipment, such as computers that include electronic switching devices. These “nonlinear loads” have the potential to create harmonic distortion, resulting in overloading the neutral conductor. Sharing the neutral would increase the likelihood of overloading the neutral conductor. This information can be found in 605.8(D) relating to cord-and-plug connected freestanding type office partitions.
Motor service factor
What is the service factor of a motor?
Service factor is a margin of safety. If the motor manufacturer designs a service factor into his motor, it means the motor will develop more than its rated horsepower (hp) without taking damage. For example, a 10-hp motor with a service factor of 1.15 can be allowed to develop 11.5 hp current without damage to the motor-winding insulation. The NEC allows a motor with a service factor of 1.15 to use overload protection of 1.25. This is found in Section 430.32(A)(1). If the motor were to develop an overload of 1.15 percent, the motor branch--circuit conductors would not be affected because Section 430.22 requires these conductors to be sized at 125 percent of motor full-load current.
Definition of ‘outlet’
We recently rewired a large condominium. We installed arc-fault circuit interrupters (AFCI) for all circuits that supplied outlets per Section 210.12(A). The lighting fixtures are wired on separate circuits from the outlets. The electrical inspector indicated that Section 210.12(A) of the NEC requires AFCI protection on the lighting circuits, too. Upon reading Article 210.12(A), I found there is no mention of lighting circuits. Is the inspector right?
Too often readers confuse the term outlet with receptacle. There are receptacle outlets, lighting outlets and device outlets. NEC 210.12(A) references branch circuits supplying outlets installed in dwelling units. This means all lighting outlets and all receptacle outlets. All of these branch circuits are required to be protected by a listed AFCI, combination-type. Check out the definition of “outlet” in Article 100.
Equipment grounding conductor requirement
If I use electrical metallic tubing (EMT) as the raceway for a motor branch circuit and flexible metal conduit (FMC) for the connection to the motor, do I need to install an equipment grounding conductor?
NEC 348.60 requires that, when FMC is used to connect equipment where flexibility is required, a separate equipment grounding conductor must also be installed.
Circuit for a refrigerator?
I installed a duplex receptacle for a refrigerator on its own circuit instead of putting it on the small-appliance branch circuit. Now I’m being told that it must be a single receptacle. Is this correct?
NEC 210.52(B)(1) requires receptacle outlets for refrigeration equipment to be served by the 20-ampere (A), small-appliance branch circuits. Exception No. 2 permits the receptacle outlet for the refrigeration equipment to be supplied from an individual branch circuit rated 15A or greater instead of being served by the small-appliance branch circuit. An individual branch circuit is defined as a “branch circuit that supplies only one utilization equipment.” Using a duplex receptacle would permit more than one utilization equipment to be supplied. Compliance with 210.52(B)(1) Exception No. 2 requires that a single receptacle must be used on a circuit rated 15A or greater. NEC 210.21(B)(1) requires a single receptacle installed on an individual branch circuit to have an ampere rating not less than that of the branch circuit. If you use a 20A rated branch circuit, you must also use a 20A rated receptacle, but if you use a 15A rated circuit, the Code allows you to use either a 15- or 20A rated receptacle.
Electric hand dryers disconnecting means?
Electric hand dryers are generally rated 15 or 20A at 120V. I believe the majority of that load is electric resistance heat. Do these installations require a disconnecting means per Article 422? I have never seen one installed with a disconnect and have only seen one dryer that could be turned off by pressing the on button again. I have never seen one that appeared to have any sort of unit switch per 422.34. It seems to me that disconnect switches are required per 422.30 unless the circuit breaker serving the hand dryer is within sight.
Electric hand dryers are rated more than 300 volt-amperes. NEC 422.31(B) permits the branch-circuit switch or circuit breaker to serve as the disconnecting means where the switch or circuit breaker is within sight of the appliance or is capable of being locked in the open position. The provision for locking or adding a lock to the disconnecting means shall be installed on or at the switch or circuit breaker used as the disconnecting means and shall remain in place with or without the lock installed. The unit switch is generally either a push switch or a photo-cell device used to turn the dryer on and a timer device to turn the unit off.
Barrier between switches?
I remember years ago a need for a barrier between two switches. One switch was 277V normal lighting, and one switch was 120V emergency lighting. I believe 404.8 is the Code reference, but it is unclear to me how to explain it to my students.
NEC 404.8(B) tells us that, where two or more phase conductors of a 480Y/277V system enter a box where switches or switches and other devices are ganged in the box, barriers are required between the devices so that the voltage between adjacent devices does not exceed 300V. However, you may be thinking about using a double-pole switch to switch a 277V fan and a 120V lighting fixture, which may be in a commercial bathroom. This is not permitted by 404.8(C) unless the multipole switch is listed and marked as two-circuit.
Water heater circuit requirement
What size branch circuit is required for a 40-gallon water heater in a single-family dwelling? The nameplate rating is 4,500 watts (W) for each of two elements.
The arrangement of the thermostat will only permit one of the 4,500W elements to be connected at a time. Using a nominal 240V circuit, 4,500 ÷ 240 = 18.75A. Section 422.13 requires that a water heater with a capacity of 120 gallons or less be considered a continuous load for the purpose of sizing branch circuits. Section 422.10 requires that the branch-circuit rating for an appliance that is a continuous load shall not be less than 125 percent of the marked rating. Based on the computation above, 18.75 1.25 = 23.4A. Although Table 310.16 shows a 12 AWG conductor as having an ampacity of 25A, the asterisk directs us to 240.4(D)(5), where we find that a 12 AWG conductor is limited to 20A for our purposes. Therefore, the minimum size conductor is 10 AWG, and the overcurrent protection or branch-circuit rating is either 25 or 30A.
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