Grounding Systems Permitted to Be Connected on the Supply Side of the Disconnect
By: Jerry Durham | Dec 02, 2019
Section 250.25 is brand new for the 2020 Code cycle. It has been created to establish grounding and bonding rules for add-on disconnects, such as a PV system disconnect acting as that PV system’s service equipment, when the disconnect is attached to conductors on the supply side (meaning before the main cut-off) of the utility service disconnect.
Section 230.82 provides electricians with a list of equipment/systems that can legally connect to the conductors on the supply side of an electrical system serving a home or business. The new Section 250.25 outlines grounding and bonding rules for a disconnect serving just such an add-on system.
Section 250.25 in the 2020 NEC
The new requirements for grounding and bonding add-on disconnects:
250.25 Grounding (of) Systems Permitted to Be Connected on the Supply-Side of the Disconnect.
This section will cover the grounding (and bonding) of systems connected on the supply-side of the service disconnect, as permitted in 230.82, when in enclosures separate from the service equipment enclosure. The installation shall comply with 250.25(A) or (B).
(A) Grounded System.
If the utility supply system is grounded, the grounding of add-on systems (systems from 230.82) connected on the supply side of the service disconnect and installed in one or more separate enclosures from the service equipment enclosure shall comply with the requirements of 250.24(A) through (D).
(B) Ungrounded Systems.
If the utility supply system is ungrounded, the grounding of add-on systems (systems from 230.82) connected on the supply side of the service disconnect and installed in one or more separate enclosures from the service equipment enclosure shall comply with the requirements of 250.24(E).
Notice, add-on disconnects making their connection on the supply side conductors of an electrical service, the 2020 NEC sends us to Section 250.24. Section 250.24 is the foundation for properly grounding and bonding all new electrical services for homes or businesses and deserves careful study from all electricians.
Prior to the 2020 Code Cycle
Requirements for the grounding and bonding of electrical service disconnects, and separately derived system disconnects, already existed before the 2020 NEC. However, solar photovoltaic (PV) systems, wind electric systems, fuel cell systems, other interconnected power production systems, and the disconnects that serve as their service equipment, did not fall under traditional grounding and bonding requirements when their disconnect is connected on the supply side of the service. When this type of add-on disconnect is connected to the conductors on the supply side of the service equipment, the add-on system is connected to what amounts to the service drop or service lateral, feeding that home or business.
The 2017 NEC and earlier Code cycles contained a huge void regarding grounding and bonding requirements for these supply side connected add-on electrical systems. Yet, these systems require grounding in the same manner as any other electrical system outlined in Section 250.92.
Example
A PV System disconnect connected to the conductors on the supply side of a home electrical service is actually connected to the utility, therefore, a main bonding jumper will be required. A main bonding jumper normally connects the service neutral conductor, grounding electrode conductor (GEC), branch-circuit equipment grounds, and metal service equipment enclosure together at the first means of disconnect. A grounded conductor is also required, as it serves as the fault-path back to the utility in the case of a short-to-ground event. Finally, a connection to the existing grounding electrode system is also required.
