690.9(D) Photovoltaic Source and Output Circuits.
Code Change Summary: The previous code language in 690.9(C) has been shortened up and relocated to 690.9(D).
The previous 2011 text in 690.9(C) was confusing and allowed the use of supplemental overcurrent devices to protect PV source circuits. As well, it made mention of overcurrent device sizes that were uncommon according to 240.6(A).
The revised text in the 2014 NEC® deletes the allowance to use supplemental overcurrent devices and requires that only listed overcurrent devices be used.
Allowing only listed overcurrent devices and removing the allowance to use supplementary-type overcurrent protection, makes it clear that blocking diodes are not accepted as an overcurrent device to protect strings of PV modules wired in series.
Blocking diodes are commonly used in PV modules to ensure that reverse current from other PV series strings does not enter and damage a PV module in another string. Blocking diodes are not listed as overcurrent devices and do not comply with 690.9(D).
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:
690.9(C) Photovoltaic Source Circuits. Branch-circuit or supplementary-type overcurrent devices shall be permitted to provide overcurrent protection in photovoltaic source circuits. The overcurrent devices shall be accessible but shall not be required to be readily accessible.
Standard values of supplementary overcurrent devices allowed by this section shall be in one ampere size increments, starting at one ampere up to and including 15 amperes. Higher standard values above 15 amperes for supplementary overcurrent devices shall be based on the standard sizes provided in 240.6(A).
2014 Code Language:
690.9(D) Photovoltaic Source and Output Circuits. Listed PV overcurrent devices shall be required to provide overcurrent protection in PV source and output circuits. The overcurrent devices shall be accessible but shall not be required to be readily accessible.