Definition
A DC Disconnect is a switch that interrupts current from a solar PV array, required by NEC 690.13. It must be lockable in the open position, rated for the maximum system voltage and current, and located in a readily accessible position.
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 (SolarEdge, SMA, Sungrow, Enphase).
- Rotary disconnect (small commercial).
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.
Frequently Asked Questions
10 commonly searched questions about DC Disconnect.
What is a DC disconnect?
A switch that interrupts the DC current flowing from a PV array to an inverter. Required by NEC 690.13. Must be lockable open, rated for system voltage/current, accessible.
Where should the DC disconnect be located?
Typically at the inverter (integrated) or within sight of it. Per NEC 690.13(A), 'readily accessible' to qualified persons — typically meaning unobstructed and within 6 ft of the floor.
How is the DC disconnect sized?
Voltage rating ≥ maximum system Voc (cold-day Voc × series modules). Current rating ≥ 1.25 × Isc × parallel string count.
Does the DC disconnect need a fuse?
Not necessarily. If overcurrent protection isn't required (single source, can't be overloaded), a non-fused disconnect is acceptable. NEC 690.9 governs fuse requirements.
What labels are required?
NEC 690.13(B) requires 'PHOTOVOLTAIC SYSTEM DC DISCONNECT' plus voltage and current ratings. Plus the warning 'DO NOT OPEN UNDER LOAD' on non-load-break devices.
Can the inverter's integrated disconnect satisfy 690.13?
Yes if it's listed for that purpose. SolarEdge, SMA, Sungrow, Enphase combiner all include integrated DC disconnects meeting 690.13.
Is a load-break disconnect required?
Strongly recommended. NEC 690.15 requires the disconnect to be load-break rated unless prominently labeled 'DO NOT OPEN UNDER LOAD'. Modern integrated inverter disconnects are load-break.
How is a DC disconnect different from the rapid shutdown initiator?
DC disconnect is the manual switch for service work. Rapid shutdown is automatic/remote for firefighter safety. Many systems have both — they serve different purposes.
Can I use an AC disconnect on DC?
Only if rated for DC. AC and DC disconnects have different arc-breaking requirements; using an AC-only switch on DC can fail dangerously. Always specify DC-rated.
How many DC disconnects are needed?
One per PV source circuit or one for the combined output, per NEC 690.13. Larger systems may have multiple — typically one at the combiner output, one integrated at the inverter input.
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