Nirav Dhanani A DC disconnect is a switch that isolates the DC conductors of a solar PV system from other equipment so they can be serviced safely. NEC 690.13 requires a disconnecting means for PV system conductors and NEC 690.15 covers equipment isolation. It must be rated for the maximum system voltage and current.
Quick Facts
| Field | Detail |
|---|---|
| Term | DC Disconnect |
| Category | Solar Components |
| Standards | NEC 690.13, NEC 690.15, UL 98 |
| Rating | Match system Voc (cold-temp) and 1.25 × Isc |
| Difficulty Level | Beginner to Intermediate |
NEC 690.13 Requirements
- (A) Means to disconnect all current-carrying conductors of the PV power source from all other conductors.
- (B) Marking: “PHOTOVOLTAIC SYSTEM DC DISCONNECT” + voltage + current.
- (C) Rating ≥ Voc and ≥ 1.25 × Isc.
- (D) Readily accessible.
- (E) Lockable in the open position (NEC 110.25).
Types
- Knife switch (heavy-duty industrial).
- Fused safety switch (typically Square D, Bussmann).
- Inverter-integrated: built into central inverters and microinverter systems from SolarEdge, SMA, Sungrow, and Enphase.
- Rotary disconnect (small commercial).
In the physical wiring path, the DC disconnect sits downstream of the array’s source-circuit junction boxes and field-terminated MC4 connectors, immediately ahead of the inverter’s DC input, which is why its rating must account for the combined output of every string feeding it.
Sizing Example
System: 1,000 V system, 5 strings parallel, Isc = 13.5 A.
- Required voltage rating: ≥ 1,000 V.
- Required current rating: 1.25 × 5 × 13.5 = 84 A.
- Choose: 200 A, 1,000 V DC fused safety switch.
Standards & Certifications
- NEC 690.13, 690.15.
- UL 98, Disconnect switches.
- UL 50, Enclosure ratings.
Key Takeaways
- DC disconnect per NEC 690.13 is mandatory; readily accessible and lockable.
- Match voltage rating to system max Voc and current to 1.25 × parallel Isc.
- Use DC-rated devices only; AC-rated switches cannot break DC arcs reliably.
- Inverter-integrated disconnects from modern manufacturers typically satisfy 690.13.
- Label per 690.13(B) with system voltage and current.
Related Reading
The DC disconnect isn’t just a field component, it also has to show up correctly, with the right symbol, voltage rating, and label text, on the project’s electrical drawings. Our breakdown of solar SLD software with NEC 2023 auto-generation covers how disconnect ratings and 690.13 labeling get carried through into a bankable single-line diagram.
On projects that pair PV with battery storage, the same disconnection logic extends to the DC-coupled storage bus, the BESS glossary entry explains how that changes the picture for hybrid inverter systems. When these details need to be compiled into a permit-ready package, our Electrical CEIG Drawings service documents disconnect placement, sizing, and labeling alongside the rest of the electrical scope.
Frequently Asked Questions
4 commonly searched questions about DC Disconnect.
Is a DC disconnect required on every solar system?
Where should a solar DC disconnect be located?
What labels does a DC disconnect need?
How is a DC disconnect different from rapid shutdown?
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