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, charles@charlesRmiller.com or www.charlsRmiller.com

Articles by Charles R. Miller

August 2013
Section 240.21 in the National Electrical Code (NEC) contains feeder tap rules. As defined in 240.2, a tap conductor has overcurrent protection ahead of its point of supply that exceeds the value permitted for similar conductors that are protected as described elsewhere in 240.4. READ MORE
July 2013
Table 310.15(B)(16) is one of the most referenced tables in the National Electrical Code (NEC). It contains allowable (or maximum) ampacities for insulated conductors rated up to and including 2,000 volts (V). The ampacities listed in this table are based on specific conditions.
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June 2013
As a general rule in the National Electrical Code (NEC), the ampere rating of the overcurrent device (fuse or breaker) must not be less than the ampacity of the conductor. READ MORE
May 2013
The overcurrent device rating is a key factor when determining the correct size conductor. Article 240 in the National Electrical Code (NEC) provides general requirements for overcurrent protection and overcurrent protective devices. READ MORE
April 2013
Article 240 in the National Electrical Code (NEC) provides general requirements for overcurrent protection and overcurrent protective devices. READ MORE
March 2013
While selecting the correct size conductor is not difficult, more is involved than selecting a conductor based solely on the ampacity shown in Table 310.15(B)(16) in the National Electrical Code (NEC). READ MORE
February 2013
The rating of the overcurrent device must be considered when sizing a conductor. In accordance with 240.4 in the National Electrical Code (NEC), conductors (other than flexible cords, flexible cables and fixture wires) shall be protected against overcurrent in accordance with their ampacities specified in 310.15, unless otherwise permitted or required in 240.4(A) through (G).
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January 2013
Table 310.15(B)(16) (formerly Table 310.16) in the National Electrical Code (NEC) provides allowable ampacities for insulated conductors rated up to and including 2,000 volts (V). The ampacities in this table are based on no more than three current-carrying conductors in a raceway, cable or earth (directly buried). The ampacities are also based on an ambient temperature of 30°C. 
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December 2012
Article 240 in the National Electrical Code (NEC) provides general requirements for overcurrent protection and overcurrent protective devices. When sizing conductors, the rating of the overcurrent device must be considered. READ MORE

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