Electrical – Impact of 2020 NEC Changes on the Rule of Six and Network Topologies

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In reference to my question Main and subpanels selection in new project I was told the 2020 NEC (that my state will adopt next year) will not allow a "ranch panel" to be installed anymore.

In practice, my question is simple: if I have different buildings or spots in my property where it is desirable to have an electric panel, and I just have a single meter from the power company, what is a circuit topology allowed by the 2020 NEC to do so?

Example scenario:

  1. house with a 200A panel and a load center in the kitchen
  2. garage/workshop with a 200A panel
  3. 100A panel at the pool
  4. 100A panel in a BBQ area

If the main breaker panel is not allowed to have any extra circuits other than the main (rules of six no longer exist) how is one supposed to do the above, which to me does not seem like a very uncommon topology?

I have read about exterior disconnects, but I am not sure they are relevant in this particular case.

Best Answer

You either need a single main, or service-entrance taps/guttering with separate disconnects

NEC editions prior to 2020 permitted a service to have up to six main (service) disconnects (six throws of the hand), whether in a single enclosure (like a ranch panel) or separate enclosures. In the 2020 NEC, this changed so that each main (service) disconnect requires its own enclosure. As a result, for single-metered-service-to-multiple-building applications, you can no longer use a "rule of six" or "ranch panel" disconnect to split power, but must instead either:

  • Use separate service entrance lines from the meter to each building. This is commonly done on single-dwelling acreages and farms where the utility secondary drop lands on a central "meter pole" or "maypole", with customer conductors run from the central metering point to each building. However, the wording of Exception 3 to 230.40 limits this in a way that makes the exception likely inapplicable when accessory dwelling units are present (your problem, in other words). Furthermore, the only other language that permits this use is 547.9(A), which only applies when agricultural buildings are being fed and requires the utility to provision a poletop switch with a remote operating handle.
  • Use a single service disconnect that has all power flowing through it. This can be problematic for Class 320 and larger services, especially in a residential context where such equipment can be disproportionately expensive to the rest of the hardware involved. Limiting the use of such hefty hardware isn't always practical, either, as it may require working under the constraints of the feeder tap rules, which can be quite restrictive in terms of wiring methods and maximum run lengths.
  • Use a gutter or tap conductors with multiple service disconnects in individual enclosures. This provides the closest thing to an existing "rule of six" setup, but has the downside that the multiple boxes and tap splicing involved add size, cost, and complexity to the installation. Using a bussed gutter instead of tap connectors reduces the complexity, but adds further cost and some more size as well.
  • Or have the utility provide separate services to separate buildings. This may be the most practical thing to do with large properties, where feeder runs would become too long (several hundred feet or more) to be performed economically at secondary voltages, but obviously requires buy-in from the utility, something they are free to not give, especially if extenuating factors are not present.

Note, though, that none of this sets any limits on how many circuits a single main disconnect can feed, or impacts the applicability of the rule of six to outbuilding disconnecting means, for that matter.

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