AC Breaker Trip

What does F77 mean?

This Automatic Fault indicates that a primary or secondary AC1 or AC2 breaker has tripped in a multi-unit installation, likely due to an overload condition. The inverter will attempt to auto-clear the fault once the breaker is closed.

• Overload condition on the AC output circuit exceeding the rated current of the primary AC breaker (e.g., >125% of FLA) for an extended period.
• Short circuit or ground fault on the AC output wiring downstream of the inverter, causing instantaneous breaker trip.
• Faulty AC circuit breaker (e.g., worn contacts, internal mechanical failure) tripping below its rated current.
• Severe power quality disturbance on the grid (e.g., voltage spike, surge current) causing nuisance tripping.
• Incorrectly sized AC breaker for the connected load or inverter capacity (e.g., 20A breaker protecting a circuit drawing 25A continuously).

Click steps to track your progress.

1. 1

   1. Identify and manually reset the tripped primary or secondary AC breaker (e.g., AC1 output breaker) at the distribution panel.

2. 2

   2. Measure the load current on the AC output circuit (e.g., using a clamp meter on L1, L2, L3) and compare it to the breaker's ampere rating.

3. 3

   3. Perform an insulation resistance test (e.g., using a Megger MIT420/2) on the AC output wiring downstream of the breaker to detect ground faults or shorts.

4. 4

   4. Inspect the tripped AC breaker for any physical damage, discoloration, or signs of arcing, which could indicate internal failure.

5. 5

   5. Temporarily disconnect non-critical loads from the AC output to reduce the total load and re-test the circuit.