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For EC&M Magazine
By Mike Holt, NEC® Consultant
Here's the follow-up to yesterday's newsletter.
This includes the answers to the questions sent, so you can see how you did.
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Figure 01
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Figure 01
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For EC&M Magazine
By Mike Holt, NEC® Consultant
Here's the follow-up to yesterday's newsletter.
This includes the answers to the questions sent, so you can see how you did.
Note: The answers to these questions are based on the 2017 NEC.
Underlined text indicates a change for the 2017 NEC.
Q1. What is the NEC rule for the ampacity of flexible cords and flexible cables?
A1. (A) Ampacity Tables. Table 400.5(A)(1) lists the allowable ampacity for copper conductors in flexible cords and Table 400.5(A)(2) lists the allowable ampacity for copper conductors in flexible cords with not more than three current-carrying conductors at an ambient temperature of 86ºF [400.5].
Where the number of current-carrying conductors in a cable or raceway exceeds three, the allowable ampacity of each conductor must be adjusted in accordance with the following multipliers:
Table 400.5 Adjustment Factor |
Current Carrying |
Ampacity Multiplier |
4“6 Conductors |
0.80 |
7“9 Conductors |
0.70 |
10“20 Conductors |
0.50 |
If the ambient temperature is other than 86°F, the flexible cord or flexible cable ampacity, as listed in Table 400.5(A)(1) or 400.5(A)(2), must be adjusted by using the ambient temperature correction factors listed in Table 310.15(B)(2)(a).
Author's Comment:
• Temperature ratings for flexible cords aren't contained in the NEC, but UL listing standards state that flexible cords are rated for 60°C unless marked otherwise.
Q2. What uses are permitted by the Code for flexible cords and flexible cables?
A2. (A) Uses Permitted. Flexible cords within the scope of this article can be used for the following applications [400.10]:
(1) Pendants [receptacles”210.50(A) and boxes”314.23(H)].
(2) Wiring of luminaires [410.24(A) and 410.62(B)].
(3) Connection of portable luminaires, portable and mobile signs, or appliances [422.16].
(4) Elevator cables.
(5) Wiring of cranes and hoists.
(6) Connection of utilization equipment to facilitate frequent interchange [422.16]. Figure 01
(7) Prevention of the transmission of noise or vibration [422.16].
(8) Appliances where the fastening means and mechanical connections are specifically designed to permit ready removal for maintenance and repair, and the appliance is intended or identified for flexible cord connections [422.16].
(9) Connection of moving parts.
Author's Comment:
• Flexible cords are permitted for fixed permanent wiring by 501.10(A)(2) and (B)(2), 501.140, 502.4(A)(1)(e), 502.4(B)(2), 503.3(A)(2), 550.10(B), 553.7(B), and 555.13(A)(2).
(B) Attachment Plugs. Attachment plugs are required for flexible cords used in any of the following applications:
Portable luminaires, portable and mobile signs, or appliances [400.10(A)(3)].
Stationary equipment to facilitate its frequent interchange [400.10(A)(6) and 422.16].
Appliances specifically designed to permit ready removal for maintenance and repair, and identified for flexible cord connection [400.10(A)(8)].
Author's Comment:
• An attachment plug can serve as the disconnecting means for stationary appliances [422.33] and room air conditioners [440.63].
Q3. What uses of flexible cords and flexible cables are not permitted by the NEC?
A3. Unless specifically permitted in 400.10, flexible cords sets (extension cords) and power supply cords aren't permitted for the following [400.12]:
(1) Flexible cord sets (extension cords) and power supply cords aren't permitted to be a substitute for the fixed wiring of a structure.
(2) Flexible cord sets (extension cords) and power supply cords aren't permitted to be run through holes in walls, structural ceilings, suspended or dropped ceilings, or floors. Š
(3) Flexible cord sets (extension cords) and power supply cords aren't permitted to be run through doorways, windows, or similar openings.
(4) Flexible cord sets (extension cords) and power supply cords aren't permitted to be attached to building surfaces.
(5) Flexible cord sets (extension cords) and power supply cords aren't permitted to be concealed by walls, floors, or ceilings, or located above suspended or dropped ceilings. Š
Ex: Flexible cords can be located above suspended or dropped ceilings if installed in a metal enclosure in accordance with 300.22(C)(3).
(6) Flexible cord sets (extension cords) and power supply cords aren't permitted to be installed in raceways, except as permitted by 400.17 for industrial establishments where the conditions of maintenance and supervision ensure that only qualified persons will service the installation.
(7) Flexible cord sets (extension cords) and power supply cords aren't permitted where they're subject to physical damage.
Author's Comment:
• Even cords listed as extra hard usage must not be used where subject to physical damage.
Q4. What does the Code require when fastening flexible cords and cables at joints and terminals?
A4. Flexible cords must be installed so tension won't be transmitted to the conductor terminals [400.14]. Š
Informational Note: This can be accomplished by knotting the cord, winding the flexible cord with tape, or by using support or strain-relief fittings.
Author's Comment:
• When critical health and economic activities are dependent on flexible cord-supplied equipment, the best method is a factory-made, stress-relieving, listed device, not an old-timer's knot.
Q5. What is the Code requirement for the identification of the equipment grounding conductor within a flexible cord or cable?
A5. A conductor intended to be used as an equipment grounding conductor must have a continuous green color or a continuous identifying marker distinguishing it from the other conductor(s). Conductors with green insulation, or green with one or more yellow stripes aren't permitted to be used for an ungrounded or neutral conductor [250.119 and 400.23].
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