Relay(s) Welded

What does F21 mean?

This Manual Fault indicates that an unidentified transfer relay is faulty, or an external AC source was incorrectly wired directly to the AC output. This can lead to improper power transfer and potential damage to the inverter.

• Excessive current draw through one of the internal transfer relays causing contacts to arc and weld shut.
• Internal relay failure due to mechanical wear, high temperature, or voltage spikes.
• Incorrect external wiring, such as backfeeding a live AC source into an inverter's output port.
• Prolonged overcurrent condition on an AC output phase due to a downstream load fault.
• Logic control circuit error preventing proper de-energization of a specific transfer relay.

Click steps to track your progress.

1. 1

   De-energize all AC inputs and outputs, then individually test continuity across each internal transfer relay's contacts with the inverter off.

2. 2

   Perform a thorough visual inspection of all AC input and output wiring connections for any signs of miswiring or external AC source backfeeding.

3. 3

   Verify the integrity of all external AC circuit breakers and contactors to ensure they are opening correctly and not shorted.

4. 4

   Measure output current on all AC phases (L1, L2, L3) using a clamp meter under operational conditions to identify any sustained overcurrent.

5. 5

   Check system log data for correlation with previous fault conditions that might indicate which relay was active during overcurrent or transfer events.