National Electrical Installation Standards

Standards as High as Your Own

Tuesday, February 21, 2023


Hi Charlie, I have two (2) outbuildings, not attached to my residence. Building one (1) is a barn with a dedicated 320-amp meter base. I have installed two (2) 200-amp outdoor breaker panels on each side of the meter base. Panel one (1) is dedicated to the barn and is only used by the barn, and the 200-amp Panel two (2) is not being used. Building two (2) is a shop, and I am planning to run power from the barn (Building 1) to the shop (Building 2). I would like to run a single 2" conduit, underground, from the extra 200-amp panel and run two (2)-70-amp circuits to the shop, using #4 AWG copper conductors I have already have on hand. This would allow the shop to be divided into two (2) units, divided by an interior wall, both with a separate electric power panel. Would this be considered two (2) separate services to a single structure, even if they are in the same single conduit? Is installing two (2) 70-amp circuits large enough for this installation, or should I relocate the extra 200-amp panel on the barn, to the shop? Thanks in advance, Todd Topley


Hello Todd, thank you for submitting such a detailed question.

To answer the first question:

This would not be considered 2 separate services. From the information provided, this would be considered two (2) feeders. The NEC® does permit multiple feeders to be installed in the same conduit if the conduit is sized large enough for all of the necessary conductors.

Section 225.30(B) permits 1-6 feeders to supply the same building under the following conditions

  1. They originate in the same panelboard/distribution equipment
  2. Each feeder terminates in a single disconnecting means
  3. All disconnecting means are grouped in the same location
  4. The disconnects are marked as to which loads they serve.
  5. To answer the second question: The size of the feeders for the shop units, will be dependent on the demand of the load to be served. Article 220 provides guidance on calculating load demand for various occupancies with various types of equipment.

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CHARLIE TROUT: Charles M. Trout, better known as Charlie, was a nationally known NEC® expert and author. He served on several NEC® technical committees and is past chairman of CMP-12. In 2006 Charlie was awarded the prestigious Coggeshall Award for outstanding contributions to the electrical contracting industry, codes and standards development, and technical training. Even though Charlie passed away in October of 2015, his work continues in spirit. NECA continues to maintain this question forum for its many subscribers in memory and recognition of all his significant contributions to making the NEC what it is today.

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