National Electrical Code Articles and Information

National Electrical Code Tips: Article 690 -- Solar Photovoltaic Systems, Part 2

Part II of Article 690 provides the circuit requirements for PV systems. These are not the same thing as the wiring methods and materials (covered in Part IV)

1. With the 2020 revision, much of 600.7 was completely rewritten. It was heavily revised again with the 2023 revision. So when determining the maximum voltage of PV system dc circuits, read carefully. This value is critical, because you must use it for all sorts of things such as conductors, equipment, and working space.
    
2. The maximum current calculation has not appreciably changed from the 2017 NEC. It's still somewhat complicated, because the method you must use depends upon the characteristics of your system. For example, if your PV system has an inverter capable of under 100KW then the maximum current is the sum of the short-circuit current ratings of the PV modules connected in parallel multiplied by 125%. But if the inverter is capable of 100KW or more, then you can use a different method but to do so you must have a documented and stamped (by a licensed PE) PV system design [690.8(A)(1) and (2)].
   
3. If a circuit is protected by an OCPD not exceeding the conductor ampacity, you can make the maximum current value equal to the rated input current of the electronic power converter input to which it is connected [690.8(B)].
    
4. You'll find two other type of maximum current calcuations, in 690.8(C) and 690.8(D). These are "Systems with Multiple Direct-Current Voltages" and "Sizing of Module Interconnection Modules", respectively. The latter was completely rewritten with the 2023 revision.
    
5. The overcurrent protection rules are in 690.9. The first rule is this: PV system dc circuit and inverter output conductors and equipment must be protected against overcurrent.
   
6. You may have circuits where overcurrent protection is not required, for example where the conductor ampacity is sufficient for the maximum current [690.9(A)(1)]. And/or you may have circuits were overcurrent protection is required only at one end [690.9(A)(2)]. There are also "other circuits", which are those that don't comply with either of the preceding requirements. Those must be protected by one of the methods listed in 690.9(A)(3).
    
7. Any OCPD you use in a PV system must be listed for use in PV systems [690.9(B)].
    
8. Install overcurrent protection for power transformers per 705.30(F) [690.10(D)].
    
9. Arc fault protection is required for any PV system with PV circuits operating at 80 VDC or greater (between any two conductors [690.11].
    
10. Any PV system installed in or on a building must have a rapid shutdown function [690.12]. The reason for it is to protect firefighters. The requirements for this are fairly detailed.

Bonus material:

"Saving the planet" is not a reality-based reason to install solar. Over the life of the installation, the carbon per watt is almost as much as it is for a modern coal-powered generating station. And have you ever noticed that there are no trees at a solar farm? Some good reasons to install solar include:

1. As a backup in case of a utility outage.
2. As as supplemental energy source to allow for a demand increase. A factory might, for example, install a solar power source for a new machine rather than go through a utility service upgrade.
3. As a means of reducing or eliminating peak loading charges.
4. To supply a remote building such as a ranger station.
5. To supply a remote operation or piece of equipment.