specifying conductors for a job & Ch 3 of NEC

[iblittljn]

Hope this is not too much of a "how to" question:

I need to spec conductors for a project. I can gather info from the ME's and CE's about environments, spaces and do the calcs needed to determine ampacity required for the various loads and run lengths.

Chapter 3 of the NEC provides wiring methods. In some cases it provides detailed info on certain cable types (UF MC AX or what ever) and how they can be used and not used. In other cases, there are cable types that are only listed in Tables. Ex THWN-2 = wet and dry locations.

Does the fact that a cable such as THWN-2 is not explicitly described in a separate article mean it can be used in accordance with a table, any wet or dry location, not otherwise prohibited by the code?

 

[charlie b]

Re: specifying conductors for a job & Ch 3 of NEC

There is nothing wrong with an engineer asking a "how to" question, so long as it is not along the lines of "how to do wiring at my own home."

THWN-2 is explicitly described in Chapter 3. THWN is in Table 310.13, and the "-2" is defined in the notes that follow that Table.

 

[rbalex]

Re: specifying conductors for a job & Ch 3 of NEC

The general progression starts in Article 300; specifically Section 300.5 which states the permitted applications of conductors specified in Table 310.13. In addition Tables are brought into the Code ?by reference? from a Section normally numbered the same as the Table. In this case, Section 310.13. Therefore conductors specified in Table 310.13 must also be installed consistent with Sections 300.5 and 310.13 and with Notes included with the Table.

A general ?Rule of Interpretation? states where specific means or methods are required all other means and methods are prohibited in absence of a declared ?Exception.? Another ?Rule of Interpretation? states that, in absence of an irreconcilable conflict between two requirements, an installation must comply with all applicable requirements.

Conductors in Table 310.13 must be installed per a recognized Chapter 3 wiring method. [300.5 ?shall be?] All other ?wiring methods? are prohibited. Since there is no inherent conflict between the ?shall be? in 300.5 and the ?shall be permitted? in 310.13, the 300.5 requirement prevails.

 

[mvannevel]

Re: specifying conductors for a job & Ch 3 of NEC

Originally posted by iblittljn:

Chapter 3 of the NEC provides wiring methods. In some cases it provides detailed info on certain cable types (UF MC AX or what ever) and how they can be used and not used. In other cases, there are cable types that are only listed in Tables. Ex THWN-2 = wet and dry locations.

Does the fact that a cable such as THWN-2 is not explicitly described in a separate article mean it can be used in accordance with a table, any wet or dry location, not otherwise prohibited by the code?

Be careful here not to confuse a "conductor" with a "cable". I think that may have caused you some confusion in one of your earlier posts.