Knowing the ins and outs of cords and cables

Listen to this article

At times, electrical installations may require some sort of flexibility. Applications range from minimizing the transmission of vibration as for motors, air conditioning and refrigeration equipment, to allowing access to fixed electrical parts as in connections to luminaires, appliances, or junction boxes. Flexible wiring also permits movement of the equipment without damage to electrical circuits.

In Chapter 3 you can find the requirements for flexible wiring methods that I covered in the February edition of this column.

Flexible cords and cables are not considered wiring methods. The NEC considers cords and cables as equipment and that is why we find the installation requirements in Chapter 4, specifically Article 400, for flexible cords and cables followed by Article 402 for fixture wires.

The differences between a cord and a cable are not simple to define. A cable can be a single conductor as well as an assembly of two or more conductors to make up a cable. Look at type EO, elevator cable in Table 400.4 which describes it as a cable with 2 or more conductors. Whereas type W, Portable Power Cable, can comprise of one or up to six conductors in sizes 12 AWG up to 500 kcmil. Type W, power cable, sizes 501 through 1000 kcmil, is only available as a single conductor. Contrast that to a cord which always has at least two conductors and typically is used to connect portable equipment.

Another cord that you can find in Table 400.4 is called tinsel cord. (Type- TST, TPT) This cord is manufactured with a helical wound memory like the old handsets of a wall phone or desk phone. This allows the cord to be stretched out and retracted back, naturally minimizing the slack of the longest required length. A common application of this type of flexible cord could be the extendable, aimable, luminaire required at loading docks for semi-trucks. Or the heat lamps in commercial kitchens than require adjustable heights over the food waiting to be served to the patrons.

Additionally, the cords and cable are also rated for specific voltages. Do not assume that any type SO cord will work for 480 volts. Table 400.4 contains many types of SO cords rated from 300 volts up to 600 volts. While some types of cords and cables may be as low as 30 volts others could be as high as 1kV or even 2kV.

Ampacities for cords and cables must be in accordance with 240.5. This section specifies using Table 400.5(A)(1) for most thermoset and thermoplastic outer coverings and Table 400.5(A)(2) for 600-volt cable types, SC, SCE, SCT, and 1000-volt cables type, PPE, G, G-GC, and W. So, the ampacities tables of Article 310 are not to be used. However, we must make temperature corrections in accordance with 400.5. This NEC requirement points us to the correction tables located in 310.15(B)(1). Adjustments to cords and cables are found within each table for up to three current carrying conductors. Table 400.5(A)(1) under Column A is for three conductors and Column B is for two. You can similar columns in Table (A)(2) for one, two and three current carrying conductors for columns D, E, and F respectively. If adjustments for more than three conductors are required, then Table 400.5(A)(3) must be used.
400.10 are permissive rules for use which generally include:

• Pendants
• Wiring of luminaires
• Connections for specific portable equipment
• Elevator cables
• Connection for equipment that may require frequent interchange
• Prevention of the transmission of vibration and noise
• Appliances to permit ready removal for maintenance and repair
• Connection of moving parts
• Where specifically permitted elsewhere in the Code
• Between an existing receptacle outlet and an inlet, where the inlet provides power to an additional single receptacle outlet.

400.12 you will see where the use of flexible cords and cables are not permitted. This would include:

• As a substitute for the fixed wiring of a structure
• Where run through holes in walls, structural ceilings, suspended ceilings, dropped ceilings or floors.
• Where run through doorways, windows, or similar openings
• Where attached to building surfaces. See Exceptions
• Concealed in walls, floors, and ceilings or located above suspended or dropped ceilings. See exceptions in accordance with 300.22
• Installed in raceways, except as otherwise permitted in this Code
• Where subject to physical damage

Underwriters Laboratories (UL) has standards for proper application of flexible cords and cables under UL 62 and UL 817 contain standards for Cord Sets and Power-Supply Cords.

400.14 prohibits the tension of the cord or cable to be transferred to the terminals or joints of the connections

400.15 contain specific flexible cords that are permitted in show windows and show cases. This does not include supply cords for portable luminaires and other merchandise being displayed or exhibited.

Throughout the Code you can find permissive rules which allow for specific cord-and-plug connected appliances and equipment for use as a disconnecting means.

You can see in the table found in 400.5(A)(1) that conductor sizes appear in 11 AWG, 13 AWG or 5 AWG and other odd number sizes of the American wire gauge. The reason is the type of stranding. Often these cables and cords are constructed mainly in either bunch stranding or rope stranding. Both types use much finer strands that can make up 100’s or 1000’s of strands for each conductor. This promotes the desired flexibility for the specific application. The fine stranding also allows for a broader range in wire sizes from manufactures of flexible cables and cords.

Terminating finely stranded conductors that make up cords and cables, require special provisions to prevent damage to the strands while mechanically torquing the conductor at the terminal. The connection or terminal must be listed for fine stranding. The second option is using a listed ferrule. This may be used to retain the strands within it and protect the strands from damage as the mechanical lug is torqued.

Flexible cords and cables are ordered from the supply house differently. When ordering other cables as with Romex for example, a 12-2 cable will include an equipment grounding conductor. But for Article 400 cables and cords you must specify that. A type SJO, 12-2, 300-volt, cable will not have the necessary EGC if required. You must specify all the conductors required for your application.

The 2020 National Electric Code added a new Article 337 for Type P cable. This is not a new wiring method but a method that is now permitted in electrical installations covered in the 90.2(A) scope of the NEC. Type P cable has well over 40 years of proven survivability in harsh and adverse conditions such a land-based oil drilling and shipyards and marinas. This is now an approved wiring method even though it is called a cable, so its installation requirements are found in Chapter 3.

400.4 gives us some options to use other flexible cords and cables other than that approved in Article 400. But only if permission is granted by the authority having jurisdiction.

To summarize flexible cords and cables

• Applications Table 400.4
• Ampacities Table 400.5(A)(1) and (A)(2)
• Adjustments Table 400.5(A)(3)
• Corrections Table 310.15(B)(1)
• Uses Permitted 400.10
• Uses Not Permitted 400.12

As you can see, where the application requires flexibility, these cords and cables with finely constructed strands permit constant repetitive movement of conductors without breaking or stressing the terminations. Although increased risks of hazards could be introduced if installed in violation of the NEC, manufactures instructions, as well as any requirements mandated by OSHA.