Sizing the AC Output Breaker for Your Solar Inverter — The Step Installers Skip

Every grid-tied or hybrid solar inverter must have a dedicated AC disconnect or circuit breaker between the inverter output and the distribution panel. This breaker protects the AC wiring from overcurrent and serves as the required disconnect means under PEC 2017. Sizing it incorrectly is one of the most common code violations found during Meralco interconnection inspection.

The Correct Sizing Method

The AC output breaker is sized at 125% of the inverter's rated output current — not the panel board's main breaker, and not the inverter's peak surge rating.

Key Rules Under PEC 2017 / NEC 690

• The AC output breaker must be dedicated — not shared with other loads
• It must be accessible and lockable — Meralco linemen need to disconnect safely
• For back-fed breakers in a panel board, there must be a warning label: "WARNING — DUAL POWER SOURCE"
• The breaker must be located within 1.8m of the inverter or at the point of interconnection with the grid
• For 3-phase inverters, use a 3-pole breaker — never three separate single-pole breakers

What Meralco Inspects

During net metering application inspection, Meralco will check: correct breaker sizing, anti-islanding function test, proper labeling, and that the AC disconnect is accessible. A wrong breaker size is grounds for rejection and re-inspection — delaying your net metering approval by weeks.

Use the free Inverter Output Breaker calculator at solarenergyph.shop to get the correct size instantly for any inverter, single or three phase.

Engr. Jason Morales — Founder, SolarEnergyPH