690.45 Size of Equipment Grounding Conductors.
Code Change Summary: A significant amount of the code section has been deleted for simplicity.
In the previous code, the size of an equipment grounding conductor for DC source and PV output circuits was dependent on whether or not ground-fault protection was provided. Now, the code language has been simplified and is much easier to apply.
Equipment grounding conductors for PV source and PV output circuits are still sized in accordance with 250.122 based on the size of an overcurrent device (if used) in a PV source circuit.
Not all PV source circuits require an overcurrent device. Deciding on whether an overcurrent device is required in a PV source circuit depends on if there are any other parallel connected source circuits that can potentially backfeed excess current into the string of modules being protected.
If there are no external current sources such as parallel connected source circuits, batteries, or backfeed from inverters, or if the short-circuit currents from all sources do not exceed the ampacity of the conductors and the maximum overcurrent device size specified on the PV module nameplate then source circuit overcurrent protection is not required (see 690.9).
When determining the minimum size equipment grounding conductor and where no overcurrent protective device is used in the circuit, an assumed overcurrent device rated at the PV maximum circuit current shall be used when applying Table 250.122. Increases in equipment grounding conductor size to address voltage drop considerations are not required. An equipment grounding conductor can never be smaller than 14 AWG.
Below is a preview of the NEC®. See the actual NEC® text at NFPA.ORG for the complete code section. Once there, click on the “free access” tab and select the applicable year of NFPA 70 (National Electrical code).
2011 Code Language:
690.45 Size of Equipment Grounding Conductors. Equipment grounding conductors for photovoltaic source and photovoltaic output circuits shall be sized in accordance with 690.45(A) or (B).
(A) General. Equipment grounding conductors in photovoltaic source and photovoltaic output circuits shall be sized in accordance with Table 250.122. Where no overcurrent protective device is used in the circuit, an assumed overcurrent device rated at the photovoltaic rated short-circuit current shall be used in Table 250.122. Increases in equipment grounding conductor size to address voltage drop considerations shall not be required. The equipment grounding conductors shall be no smaller than 14 AWG.
(B) Ground-Fault Protection Not Provided. For other than dwelling units where ground-fault protection is not provided in accordance with 690.5(A) through (C), each equipment grounding conductor shall have an ampacity of at least two (2) times the temperature and conduit fill corrected circuit conductor ampacity.
2014 Code Language:
690.45 Size of Equipment Grounding Conductors. Equipment grounding conductors for PV source and PV output circuits shall be sized in accordance with 250.122.
Where no overcurrent protective device is used in the circuit, an assumed overcurrent device rated at the PV maximum circuit current shall be used when applying Table 250.122. Increases in equipment grounding conductor size to address voltage drop considerations shall not be required. An equipment grounding conductor shall not be smaller than 14 AWG.