Growatt No AC Connection: Inverter Error 302 and Isolator Triage

Key Takeaways

• Growatt "No AC Connection" and Error 302 occur when the inverter senses an absence of grid voltage at its AC input terminals.
• The most frequent causes are a tripped miniature circuit breaker in the main consumer unit or an external rotary AC isolator in the OFF position.
• Checking the installation requires verifying that all upstream isolators are closed, inspecting terminal wiring security, and confirming that voltage matches nominal grid voltage.
• If stable AC mains voltage is present directly at the inverter connector but Error 302 persists, the internal AC detection circuit is defective and requires manufacturer service.

What does Growatt No AC Connection mean?

When a Growatt grid-tied or hybrid solar inverter displays "No AC Connection" on its screen or broadcasts Error 302 in the mobile monitoring application, the internal control board has failed to detect mains grid voltage across its alternating current terminals. Because solar inverters operate as grid-following current sources, they cannot export power without sensing a live, stable utility reference. The inverter disconnects from the home electrical system, illuminates its fault indicator, and halts generation.

For British solar installations, the electrical supply between the consumer unit and the inverter must satisfy strict isolation and protection criteria set out in our UK solar electrical installation guide.

This alarm condition protects both the equipment and utility line workers by preventing islanding during network outages. In most home installations across England, Wales, and Scotland, the error stems from an open circuit breaker, a loose screw terminal, or a regional distribution outage rather than an internal component breakdown.

Primary causes of missing AC grid voltage

Growatt service engineering documentation identifies four primary failure modes responsible for loss of AC detection:

In systems with domestic energy storage or dynamic export tracking, an unpowered AC bus also suspends battery charging and export metering; see our battery storage fire safety guide and Smart Export Guarantee guide.

Step-by-step diagnostic workflow

To triage No AC Connection and Error 302, follow this systematic troubleshooting sequence:

Step 1: Verify grid supply and switchgear positions

Check whether the rest of your home has mains electricity. If household lights and appliances are unpowered, check with your local Distribution Network Operator (DNO) to confirm whether a regional power cut has occurred. Restore grid supply if interrupted before troubleshooting further.

If household power is normal, navigate to the dedicated solar generation sub-board or main consumer unit. Locate the solar generation breaker and verify that both the breaker and any associated residual current devices are in the ON position. Next, inspect the external AC rotary isolator mounted adjacent to the Growatt inverter and verify it is set fully to the ON position.

Step 2: Perform a safe dead wiring continuity check

If the breakers and isolators are engaged but the inverter still reports Error 302, a loose connection may have severed the circuit:

1. Isolate the solar AC circuit at the main consumer unit.
2. Turn the external AC rotary isolator to OFF.
3. Turn the integrated inverter DC switch to OFF.
4. Check the AC wiring after shutdown to verify terminal integrity.
5. Inspect all screw clamps inside the rotary isolator enclosure and AC connector plug.
6. Tighten or repair AC connections as needed to eliminate high-resistance joints.

Step 3: Measure AC terminal voltage

A certified electrician uses an approved two-pole voltage tester to verify live conductors:

1. Re-energize the AC isolator switch while leaving the inverter disconnected.
2. Measure AC voltage at inverter terminals (should match nominal grid voltage).
3. Test line-to-neutral, line-to-earth, and neutral-to-earth potentials.
4. Check the AC terminals for correct mechanical seating. If Error 301 appears instead, the phase and neutral conductors are inverted and must be swapped.

Step 4: Execute a controlled system re-energisation

Once stable voltage is verified at the terminal plug:

1. Insert the AC connector firmly into the base of the inverter until the locking ring clicks.
2. Turn on the AC consumer unit breaker.
3. Turn the external AC rotary isolator to ON.
4. Turn on the inverter integrated rotary DC switch.
5. Restart inverter after confirming stable AC voltage presence.
6. The inverter will initiate a countdown timer before closing its internal grid synchronisation relays and resuming generation.

For micro-generation notification rules and grid synchronisation delays, refer to our micro-generator grid connection guide.

Safety: alternating current electrical hazards

Mains alternating current presents severe shock and electrocution risks. Electrical inspection must observe rigorous safety controls:

• Safe isolation before opening enclosures: Never open the cover of an external rotary isolator, junction box, or consumer unit without first isolating the circuit and locking off the supply.
• Proving dead: Always test your voltage detector against a known live proving unit before and immediately after checking the inverter AC terminals.
• Capacitor discharge time: Even after disconnecting AC and DC supplies, internal inverter capacitors retain lethal charge. Wait several minutes for the display to power down completely before unplugging connectors.

When to contact an MCS-certified technician

Homeowners can safely check the consumer unit toggle positions and confirm whether external power cuts have occurred. However, testing terminal voltages, opening switchgear enclosures, and rewiring connector plugs must only be performed by certified professionals with valid electrical qualifications.

Escalate to your MCS-certified installer under these conditions:

• The consumer unit breaker trips immediately: If the breaker trips instantly upon switching the AC isolator on, a short circuit or earth fault exists along the cable run.
• Terminal voltage is missing despite closed breakers: A blown service fuse or broken buried cable core requires professional fault-finding instruments.
• Voltage is present but Error 302 persists: If multi-meter testing proves nominal grid voltage is reaching the terminal pins, the internal AC detection circuit issue prevents the inverter from reading the supply.

In case of persistent hardware failure where field wiring is proven sound, the only authorized path for repair is contacting the official Growatt Service Department at service@growatt.tech.