To the uninitiated, this topic sounds like a simple one. But turn to Article 400, and you see Table 400.4 that, with its extensive table notes, takes up five full pages plus a nearly full sixth one. Then you have Tables 400.5(A)(1), 400.5(A)(2), and 400.5(A)(3) after that.
Article 400 consists of Parts I and II. Part II provides the construction specifications, so the typical installer can ignore them (manufacturers cannot); the same is true of the marking requirements in 400.6.
General tips:
- If your intended use is not one of the 11 permitted uses [400.10], don’t use a flexible cord or cable. Move on to another wiring method.
- Similarly, don’t use a flexible cord or cable for prohibited use, such as a substitute for the fixed wiring of a structure [400.12].
- Before using any NEC table, read the notes. Even though they come at the end, read them first. Otherwise, your use of the table will be inefficient and possibly wrong.
- Use flexible cords and cables suitable to the application [400.3]. How do you know what’s suitable? Use Table 400.4.
- What if it’s not in the table? Then don’t use it [400.4].
- Use the correct size and type for the application, per the tables [400.5(A)].
- Don’t splice a flexible cord or cable when installing it [400.13]. You can repair an existing one by splicing, however.
- Connect in a way that doesn’t transmit tension to joints and terminals [400.14]. For example, use the correct strain relief(s) while also providing adequate support.
All the tables have notes, but here are two things to consider from the Table 400.4 notes:
- There are two unenumerated notes to the table. These are for the manufacturer but may be useful for the installer. Some flexible cords and cables are required to have individual conductors twisted together; others are not. How can it help to know which ones are which? For those that are, induction is the issue. Don’t run their conductors in parallel once they leave the cord or jacket cable; twist them or separate them with space. A barrier doesn’t stop induction, but distance weakens it.
- The 11 enumerated notes are what would be called back notes in a research paper. They aren’t general notes; each one is referenced from within the table itself for a specific type of flexible cord or cable. If you look in the Type Letter column, you will see numbers in superscript next to the type letters for many, but not all, flexible cord or cable types. Type C (Lamp Cord) has no back note. But the very next entry, Type E (Elevator Cord), has four back notes. Type EC (Elevator Cable) has only three back notes. Always go by the Type Letter, not by the trade name (if you look at the tradename Portable Power Cable, you will see why).
Rushing through Article 400 by quickly glancing at a table to see if your ampacity is right doesn’t really save time. Spending a few more minutes to ensure everything else is right does.
