Charles R. Miller

Code Contributor

Charles R. Miller, owner of Lighthouse Educational Services, teaches classes and seminars on the electrical industry. He is the author of “Illustrated Guide to the National Electrical Code” and NFPA’s “Electrical Reference.” He can be reached at 615.333.3336, or

Articles by Charles R. Miller

February 2012
When sizing conductors, the number of current-carrying conductors installed in a raceway or cable must be considered. No conductor shall be used in such a manner that its operating temperature exceeds that which is designated for the type of insulated conductor involved [310.15(A)(3)]. READ MORE
January 2012
Table 310.15(B)(16) (formerly Table 310.16) in the National Electrical Code (NEC) provides allowable (or maximum) ampacities for insulated conductors rated up to and including 2,000 volts (V). The allowable ampacities in this table are based on two stipulations: adjacent load-carrying (current-carrying) conductors and ambient temperature. READ MORE
December 2011
Allowable ampacities for insulated conductors rated up to and including 2,000 volts (V) are in Table 310.15(B)(16). This table underwent a number change in the 2011 edition of the National Electrical Code (NEC). Before, this table was numbered 310.16. READ MORE
November 2011
Safety is the main reason for the existence of the National Electrical Code (NEC). Its purpose is the practical safeguarding of persons and property from hazards arising from the use of electricity [90.1(A)]. Ensuring conductors and overcurrent protective devices are sized correctly is one aspect of practical safeguarding. READ MORE
October 2011
The National Electrical Code (NEC) is revised every three years. The renumbering of Table 310.16 to Table 310.15(B)(16) was a significant change in the 2011 edition. READ MORE
September 2011
Sizing conductors is not a difficult task, but more is involved than referencing just one section, one article or even one chapter in the National Electrical Code (NEC). To select the correct conductor size, it is necessary to reference several sections throughout the Code. Before referencing the NEC, certain information is needed. Gather it by answering some key questions. READ MORE
August 2011
Whether conductors are supplying power to branch circuits, feeders or services, the ampacity must not be less than the load. The load can be an actual load, or it can be calculated in accordance with the requirements in Article 220 of the National Electrical Code (NEC). READ MORE
July 2011
Many factors are involved when sizing conductors. Specifications for sizing conductors are not just in one section or even one article of the National Electrical Code (NEC). Although the maximum allowable ampacities for conductors are listed in Table 310.15(B)(16) (formerly Table 310.16), other provisions must be considered. Section 110.14(C) must be acknowledged when sizing conductors. READ MORE
June 2011
Selecting the correct size conductor involves referencing more than one section and more than one chapter in the National Electrical Code (NEC). The following questions must be answered before selecting conductors. What is the lowest temperature rating of any connected termination, conductor or device? What is the connected load, or what is the calculated load in accordance with Article 220? READ MORE