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EC&M Tech Talk — Separately Derived Systems

May 1, 2025

Randy breaks down everything you need to know about separately derived systems.

In this EC&M Tech Talk Randy Barnett, Electrical Codes Manager at NTT Training, first explains the definition found in Article 100 of the NEC® for “Separately Derived Systems.” Once the definition is understood the most common types of these systems are explained. They include distribution transformers and automatic transfer switches. Next, NEC rules are addressed.

Article 250 Grounding and Bonding has specific requirements for the grounding and bonding of separately derived systems. These are found in Sec. 250.30 and consists of three subsections. An overview and some specific wording is examined in each of these subsections. Another commonly installed separately derived system is the Solar Photovoltaic (PV) System. These systems are covered in NEC Article 690. Part V of this article provides requirements for grounding and bonding. The Tech Talk identifies each of the subsection requirements.

Proper installation of separately derived systems is a must. Otherwise, systems and equipment will not operate properly, and safety will be in jeopardy. Use this EC&M Tech Talk to decide if you have such a system and where to find the rules for proper installation.

About the Author

Randy Barnett | CESCP

Randy Barnett is an NFPA Certified Electrical Safety Professional, a long-time journeyman electrician, instructor and author with expertise in industrial electrical construction and maintenance. He is Electrical Codes & Safety Manager for NTT Training. Because of his ability to develop and deliver quality programs, Randy has trained more than 10,000 students in all 50 states, including Canada, Singapore, Afghanistan, Dubai, Trinidad, and Saudi Arabi. His articles appear in numerous trade publications and, his book on "Commercial and Industrial Wiring" is used as an entry-level text in many electrician training programs. Randy also appears at various corporate and trade association speaking engagements and consults on training program design and implementation. Randy is a graduate of the U.S. Navy Nuclear Power School, served as a nuclear electrician in submarines and holds a B.S. in business.