AC Disconnect: NEC 705 Solar Utility Disconnect & Lockable Visible-Open Requirements

Definition

An AC Disconnect is a switch on the AC side of a solar PV system that interrupts current from the inverter output to the utility service. NEC 690.15 and most utility tariffs require it to be lockable in the open position with a visible blade or contact.

Quick Facts

Field	Detail
Term	AC Disconnect
Category	Solar Components
Standards	NEC 690.15, NEC 705.20, UL 98
Typical Rating	30–200 A, 240–480 V
Difficulty Level	Beginner

NEC 690.15 Requirements

Disconnect between inverter and utility service.
Lockable open with provision for lockout/tagout.
Visible-blade or visible-open indicator.
Within 10 ft of the meter (utility-specific).
Labeled per NEC 690.13(B): “AC DISCONNECT FOR PV SYSTEM.”

Types

Square D heavy-duty safety switch (residential dominant).
Eaton DG-series (residential alternative).
Bussmann fused/non-fused safety switches.
Inverter-integrated AC breakers (some utilities accept).

Sizing Example

8 kW residential inverter, 240 V output:

Continuous output current: 8000 / 240 = 33.3 A.
Sizing: 1.25 × 33.3 = 41.7 A → 60 A standard rating.
60 A, 240 V AC disconnect (e.g., Square D DU222RB).

Best Practices

Specify outdoor-rated (NEMA 3R minimum) for outdoor installations.
Locate near the meter for utility personnel access.
Use load-break-rated devices.
Maintain clear unobstructed access (NEC 110.26 working clearance).
Label clearly per NEC 690.13(B) and utility tariff.

Standards & Certifications

NEC 690.15, 705.20.
UL 98 — Disconnect switches.
UL 489 — Circuit breakers.

Key Takeaways

AC disconnect required by NEC 690.15 between solar inverter and utility service.
Must be lockable open with visible-open indicator.
Sized to 1.25 × continuous AC output; voltage rating to system voltage.
Most utilities require an exterior AC disconnect near the meter for line-worker safety.
Label per NEC 690.13(B) and any utility-specific tariff requirements.

Frequently Asked Questions

10 commonly searched questions about AC Disconnect.

What is an AC disconnect?

A switch that interrupts the AC output of a solar inverter before it reaches the utility service. Required by NEC 690.15 and most utility tariffs. Must be lockable open with visible blade contacts.

Where is the AC disconnect located?

Typically near the main electrical service panel, externally accessible to utility personnel. Some utilities require it outdoors and within 10 ft of the meter.

Why is the AC disconnect required?

Allows utility line workers to physically isolate the solar system during maintenance, preventing back-feed onto a de-energized circuit. Critical safety device.

Does the AC disconnect need to be visible?

Yes, per most utility tariffs — must have a visible open contact or blade so workers can confirm de-energization. Sealed enclosures with indicator lights don't always qualify.

Can the inverter's integrated AC breaker replace the AC disconnect?

Sometimes. Some utilities accept integrated breakers; others require a separate exterior disconnect. Check the utility's tariff.

How is the AC disconnect sized?

Voltage rating ≥ system voltage (240 V residential, 480 V commercial). Current rating ≥ 1.25 × continuous AC output current.

Is the AC disconnect a load-break device?

Yes. It must be capable of interrupting full inverter output current under load. Specify load-break rated for the application.

How does the AC disconnect interact with rapid shutdown?

Opening the AC disconnect typically triggers rapid shutdown (inverter loses AC reference → shuts off DC). The two work together for safe service.

Can an existing main service breaker serve as the AC disconnect?

No. NEC 690.15 requires a separate, dedicated solar AC disconnect for service personnel isolation. The main breaker stays in place for the rest of the service.

Are AC disconnects required for microinverter systems?

Yes. Even with microinverters, an AC disconnect for the combined trunk feeder is required before utility interconnection.