National Electrical Code Explanations

Based on the 2020 NEC

by Mark Lamendola

National Electrical Code Tips: Article 840, Premises-Powered Broadband Systems


  1. Article 840 is the last Article in the NEC (as of the 2020 Code). It is not the last place to find valuable information. Past this point in the NEC you'll find useful tables an annexes.
  2. The Scope of Article 840 has expanded and contracted over the past few Code cycles. Now the Scope is the same as the title of the Article. Much simpler that way.
  3. Part I contains principles/requirements that are found elsewhere in the NEC repeatedly, except here you get referred to other places to read them: 1. Mechanical execution of work needs to be neat and workmanlike [820.24]; Abandoned cables have to be labeled as such [840.25]; and 3. You can't substantially increase the spread of fire [840.26].
  4. Part II is titled "Cables Outside and Entering Buildings". Most of the text provides requirements for optical cables [840.47(A)]. You'll find a couple of quick blurbs about communications wires and cables [840.47(B)] and coaxial cables [840.47(C)].

  5. What if you have unlisted wires and cables entering buildings? Those are covered by 840.48..
  6. Part III provides "protection" requirements. It does so in a verbose and convoluted way. Basically, you must either ground (bond to the equipment grounding jumper) these incoming cables or install an interrupting device on them.
  7. Part IV contains the "grounding" requirements. Much of this is done by referring to other requirements. That makes sense for consistency of application, but following all these text jumps can be confusing. If you're going to do a project covered by Article 840, look up all of the "grounding" (it's typically bonding, instead) requirements and write them down in one place. Alternatively, you can just note that if it's metallic it needs to be bonded to the equipment bonding jumper and that includes any driven ground rods. Do not drive a ground rod for this system and let it float relative to other ground rods; that creates a dangerous difference of potential.
  8. In Part IV, premises circuits leaving the building are covered separately [840.102].


  9. Part V provides requirements for installation methods within buildings. Part V is extremely short, and consists of 840.133 which is not much. It tells you to apply the requirements of 770.133.
  10. The communications cables can carry power wiring, too [Part VI]. The text here has been extensively revised with the 2020 NEC.