Anti-islanding function malfunction

This symptom shows up as status code 456 on Fronius Primo and Fronius Symo inverters. The code means the inverter's anti-islanding function is no longer running as it should. Anti-islanding is a grid-protection function that inverters must have. One manufacturer states that its anti-islanding protection meets the UL1741 and IEEE1547 requirements. Several inverters detect islanding actively by shifting the frequency. Monitoring the largest frequency change is described as an addition to islanding detection. The sources give no root cause or fix for this code. Use the manufacturer's status code documentation as the reference when the code appears.

<!-- review notes

• sentence 1: support check: partial - Code 456 meaning is stated, but the passages don't mention Primo or Symo models.
• sentence 2: support check: partial - The UL1741/IEEE1547 compliance claim is stated, but not that anti-islanding is a function inverters must have.
• sentence 4: support check: partial - Passages give no cause or fix (consistent), but nothing in them recommends the manufacturer's documentation as the reference.
• sentence 4: review: partial - The rows do list no cause or remedy for code 456, but the advice to use the manufacturer's status-code documentation as the reference is not in the passages. -->