National Electrical Code Top Ten Tips: Article 409 -- Industrial Control Panels

by Mark Lamendola

Based on the 2021 NEC

Please note, we do quote from copyrighted material. While the NFPA does allow such quotes, it does so only for the purposes of education regarding the National Electrical Code. This article is not a substitute for the NEC.

These are the 10 NEC Article 409 items we deem most important, based on the pervasiveness of confusion and the potential costs of same.

  1. Any control panel operating at 1000V or less must comply with Article 409 [409.1].
  2. An industrial control panel can have control circuits, power circuits, or both.
  3. Quite a few other Articles apply to these panels, in addition to the specific requirements of Article 409. See Table 409.3. For example, if the industrial control panel is for a rail crane, Article 610 also applies.
  4. Base the ampacity of the supply conductor on the sum of three items [409.20]:
    A. 125% of the full-load current rating of all resistance heating loads (combined).
    B. 125% of the full-load current rating of the highest rated motor.
    C. Sum of the full-load current rating of all the other motors (and apparatus) that may be operating at the same time.
  5.  Provide overcurrent protection per Article 240, Parts I, II, and IX [409.21].
  6. You can put overcurrent protection ahead of the panel or inside it [409.21(B)].
  7. You do not ground an industrial control panel. You bond it [409.60]. Grounding means a path to the earth, which is fine for lightning protection. It does nothing for reducing dangerous differences of potential because it is not a low-impedance path between metallic objects or to the equipment grounding conductor or back to the source.
  8. Don't use industrial control panels as junction boxes or as any kind of feed-through system. Circuits that are not part of the panel must be routed around it, not through it. While this is not explicitly stated in Article 409, it is implicitly stated. In addition to the fact it is a control panel (read that name again), the marking requirements in 409.11 make this fairly obvious.
  9. Control cabinets have wire bending and spacing requirements. Those nice 90 degree bends for 5V systems do not belong inside a typical industrial control panel. And if wiring is voluminous, simply dumping it in a gutter or routing it inside plastic wrap isn't the solution. See 409.104 for requirements.
  10. Spacing requirements are critical. See Table 430.97(D) [409.106].