250.30 Grounding Separately Derived Alternating-Current Systems.

Multiple generators of the same type connected in parallel.
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Multiple generators of the same type connected in parallel.

Code Change Summary: Added code language regarding multiple power sources connected in parallel.

In the 2020 NEC®, Section 250.30 was expanded to make it clear that when grounding separately derived systems, multiple power systems of the same type and connected in parallel are considered one separately derived system.

Multiple transformers, engine generators, battery systems, and solar photovoltaic systems are some examples of power systems that can be connected in parallel to form one separately derived system.

Below is a preview of the NEC®. See the actual NEC® text at NFPA.ORG for the complete code section. Once there, click on their link to free access to the 2020 NEC® edition of NFPA 70.

2017 Code Language:

250.30 Grounding Separately Derived Alternating-Current Systems. In addition to complying with 250.30(A) for grounded systems, or as provided in 250.30(B) for ungrounded systems, separately derived systems shall comply with 250.20, 250.21, 250.22, or 250.26, as applicable. Multiple separately derived systems that are connected in parallel shall be installed in accordance with 250.30.

2020 Code Language:

250.30 Grounding Separately Derived Alternating-Current Systems. In addition to complying with 250.30(A) for grounded systems, or as provided in 250.30(B) for ungrounded systems, separately derived systems shall comply with 250.20, 250.21, 250.22, or 250.26, as applicable. Multiple power sources of the same type that are connected in parallel to form one system that supplies premises wiring shall be considered as a single separately derived system and shall be installed in accordance with 250.30.

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250.30 Grounding Separately Derived Alternating-Current Systems.

Below is a Real Question from our Electrical Continuing Education Courses for Electrical License Renewal:

Based on the 2020 NEC, which of the following is true?

A: Multiple power sources of the same type and connected in parallel to form one system that supplies premises wiring are considered as multiple separately derived systems.
B: Multiple power sources of different types and isolated from each other shall be considered as a single separately derived system.
C: Multiple power sources of different types and connected in parallel shall be considered as a single separately derived system.
D: Multiple power sources of the same type that are connected in parallel to form one system that supplies premises wiring shall be considered as a single separately derived system.
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