Code Change Summary: Revised language to simplify the requirements for sizing PV dc conductors.

In the 2023 NEC^®, Section 690.8(D) was revised and made into a list to eliminate the previous lengthy description on properly sizing PV system dc circuit conductors when multiple PV string circuits are connected in parallel and protected by the same overcurrent device.

Not all parallel connected PV series string circuits require an overcurrent protective device at the PV source circuit level.

Section 690.9(A)(1) provides language that applies where overcurrent protection is not required.

For PV system configurations that require an overcurrent device at the PV source circuit level, it is most common to see each PV string circuit with its own overcurrent device but sometimes the design will specify the same overcurrent device protecting multiple parallel strings of PV modules. For these designs, PV dc circuit sizing is critical since each conductor must be protected from potential backfeeding that can occur from other parallel-connected PV strings connected to the shared overcurrent device.

The informational note in Section 690.9(C) makes it clear that a single overcurrent protective device in either the positive or negative conductors of a PV system in combination with ground-fault protection specified in 690.41(B) provides adequate overcurrent protection.

The updated 2023 code language in 690.8(D) makes it clear that when an overcurrent device is used to protect more than one set of parallel-connected PV string circuits, the ampacity of each conductor protected by the device shall not be less than the sum of the following:

(1) The rating of the overcurrent device

(2) The sum of the maximum currents as calculated in 690.8(A)(1)(a) for the other parallel-connected PV string circuits protected by the overcurrent device

Since PV system DC circuits are coming from PV modules that are current limited and can only product a set amount of current, properly sizing the PV system dc conductors based on the maximum potential current that could be delivered from the modules and making sure the current from all sources can’t exceed the maximum overcurrent device specified on the PV module nameplate is sufficient and an overcurrent device is not required.

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 2023 NEC^® edition of NFPA 70.