National Electrical Code Articles and Information

Code Quiz: Article 310, Part 4

Based on the 2011 NEC

Questions and answers written by Mark Lamendola, who has worked as a master electrician, electrical inspector, and design engineer. Mark is an IEEE Senior Member, and the Code article author for Codebookcity.com. Since 1996, he has been writing National Electrical Code articles for electrical trade magazines and has an extensive portfolio of hundreds of NEC articles..

1. What's the important concept you need to understand about 310.18?
    

2. Many electricians and electrical engineers say you can't use the 90 degree column of the ampacity tables in Chapter 3. Why would they say this, and what's going on there? Why is the 90 degree column provided?
    

3. If you have four conductors in a raceway, can you use Table 310.15(B)(16) for the ampacities?
    

4. What's the difference between Table 310.15(B)(16) and Table 310.15(B)(17)?
    

5. "I'm designing power distribution within my facility, and I need THHN conductors that can carry 780A each. But the table goes up only to 750A. What should I do?"

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