Overcurrent protection means using fuses or circuit breakers, called OCPDs, to protect conductors and equipment from excess current. In PV systems, the dc circuits and the inverter output conductors and equipment must be protected against overcurrent. An OCPD is not required when the conductors have enough ampacity for the highest current available to them. PV modules and inverter outputs can supply only limited current. Protection is needed where they connect to stronger sources such as parallel strings, batteries or the utility, and the device usually goes at that stronger-source end. OCPDs in PV dc circuits must be listed for PV use, because dc faults are much harder to interrupt than ac faults. Devices marked only for ac should not be used in dc circuits. As a general rule, an OCPD is sized at 125% of the continuous load current, and its rating normally should not exceed the ampacity of the conductors it protects. Where single OCPDs protect source or output circuits, they must all be in the same polarity. Combined with the required ground-fault protection, one device in either conductor gives adequate protection. On interconnections, the rating of the OCPD that protects a busbar is part of the 120% busbar rule. A backfed breaker must be suitable for backfeed and carry a label warning not to relocate it. How fast an OCPD clears a fault strongly affects arc flash incident energy. Upstream and downstream devices may need to be selectively coordinated.
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related_toAn OCPD is not needed where conductors have enough ampacity for the highest available current; the OCPD rating normally should not exceed conductor ampacity.
sec=h15 h=3ddeddb2f95fsec=h54 h=01989f804c87sec=h22 h=a0abbaeecc7esec=h6 h=0ace453bcb69verified by: review-workflowverified on: 2026-10-24
c2 verified · fact 120% busbar rule
Busbar rating checks add 125% of the source output current to the rating of the OCPD protecting the busbar.
sec=h130 h=32024b578c3csec=h25 h=c63742cb1b49sec=h9 h=6de44b94103fsec=h11 h=e729ef3b6f0fsec=h49 h=0f64065acf47verified by: review-workflowverified on: 2026-10-24
c3 drafted · lead Continuous load
As a general rule, fuse or breaker ampere rating is selected at 125% of the continuous load current.
sec=h6 h=0ace453bcb69sec=h6 h=0ace453bcb69c4 drafted · lead Arc flash incident energy
The protective device's clearing time at the expected arcing current is a key determinant of incident energy.
sec=h5 h=086b216ff4ecc5 drafted · lead Protection coordination
Upstream and downstream OCPDs may need to be selectively coordinated; zone-selective interlocking lets the lower-tier device clear the fault first.
sec=h74 h=1a0128d8c989sec=h6 h=23fbcd0d8d68sec=h86 h=26b219c15da4c6 verified · fact DC ground-fault protection
With the improved PV ground-fault protection, a single OCPD in either the positive or the negative conductor gives adequate overcurrent protection.
sec=h27 h=4230f59325bdsec=h58 h=165f8191a30bsec=h8 h=f17153ed396everified by: review-workflowverified on: 2026-10-24
c7 verified · fact NEC 2017 690.9(C) Overcurrent protection: photovoltaic source and output circuits proposed
sec=h27 h=4230f59325bdsec=h15 h=3ddeddb2f95fsec=h8 h=f17153ed396everified by: review-workflowverified on: 2026-10-24
c8 drafted · lead String protection fuse
String OCPDs must be fitted and correctly specified where used.
sec=h169 h=6309d78dae0areview note: support check: partial - u4 says string OCPDs must be fitted and correctly specified, but it is an IEC TS 62548 inspection checklist item rather than an explicit link to overcurrent protection in general.
c9 drafted · lead AC circuit breaker proposed
sec=h6 h=0ace453bcb69sec=h6 h=0ace453bcb69review note: support check: partial - The passages cover fuse and circuit breaker ratings generally and mention inverse-time breakers, but they never address an AC circuit breaker as a PV component.
c10 drafted · lead 100% rated circuit breaker proposed
An assembly listed for continuous operation at 100% of its rating may be used at 100% of its rating.
sec=h15 h=3ddeddb2f95fsec=h8 h=f17153ed396ec11 drafted · lead Backfeed from another source
Inverters, parallel strings and storage can feed fault current back into PV circuits.
sec=h169 h=6309d78dae0asec=h15 h=3ddeddb2f95fc12 drafted · lead Power control system
sec=h34 h=3594f824a3b8related_to c1related_to c8related_to c3related_to c3related_to c7related_to c1