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National Electrical Code Explanations

Based on the 2020 NEC

by Mark Lamendola

National Electrical Code Tips: Article 705, Interconnected Electric Power Production Sources

If you have a standby generator, it's probably an interconnected electric power production source. In fact, most onsite generation is interconnected. What does "interconnected" mean? We'll get to that in a moment. Just a teaser: it does not mean a power source that interacts with the grid.

Examples where the onsite power source is probably not interconnected include solar powered decorative lights and solar powered ventilation systems. These are independent systems. The lights, if not operated, pose no threat to safety or operations. The idea behind solar powered ventilation systems is you don't need them when the sun isn't bearing down heating things up. These ventilation systems may be the sole ones or they may be additional, supplemental ones to aid during peak temperatures.

So what is an interconnected power source?

A power source is "interconnected" when it operates in parallel with the primary source(s) of electricity. Though Article 705 doesn't provide the definition, we understand it from the scope in 705.1.

This does not necessarily mean a power source that interacts with the grid. There are other scenarios; this interaction with the grid is just one. The primary source might not be the grid at all. For example, a bank in Omaha, Nebraska has no connection to the grid. It uses onsite fuel cell systems as its primary source. The bank also has gas turbines as interconnected power sources.

So keep in mind that the defining characteristic of an interconnected power source is that it interacts with the primary source(s) which are not necessarily the grid. Don't assume that the grid is the primary source either, even if it is a source (it might not even be used). In some facilities, the grid is a tertiary source and that makes it an interconnected power source.

Let's address some highlights of the Article 705 requirements:

  1. As the name implies, these systems are interconnected. In our intro, we explained what that means. Don't confuse these with other systems. But also, don't make the mistake of thinking these can't also be classified as some other system. Any of the systems covered by Article 700, 701, or 702 can also be covered by Article 705. And they are covered by Article 705 if they are interconnected.
  2. Wherever you have such a system, you must post a permanent plaque or directory that denotes all power sources in or on the premises [705.10]. It makes sense to exceed this basic requirement by also installing a sign or board that has a map or drawing that shows the location of the various power sources (with You Are Here distinctly shown). For example, you can install the same sort of board that's typically used for employee communications outside the clock-in or break room areas.
  3. The "point of connection" is a critical aspect of these systems, even though that language doesn't appear in Article 705 anymore. The installation requirements vary, depending upon whether the connection is on the supply side [705.11] or load side [705.12].
  4. When making supply side connections, the disconnect must be on the service side of the fuses [705.11(C)].

  5. Supply side connections rated 1000A or more must have ground fault protection [705.11(E)].
  6. For load side connections, each source interconnection must have a dedicated circuit breaker or fusible disconnecting means [705.12(E)].
  7. When sizing busbards for load side connections, you must use one of the six methods detailed in 705.12(B)(3).
  8. If you use a power control system (PCS), it must meet the requirements of 705.13.
  9. You can use all applicable Chapter 3 wiring methods for these systems [705.23], if you follow the requirements for any particular wiring method you use.
  10. Part II provides the requirements for microgrid systems. It's pretty short. One of the things it allows is for your microgrid system to be able to disconnect from interconnected sources such as the primary source and run as an isolated system in island mode [705.50].