Onan 5.5 HGJAB Wiring Question

[KN5DX]

Troubleshooting Harmonics can be/is a unique skill set from regular service type troubleshooting. We had a 150kva service feeding an industrial building. Customer blaming us for harmonics. I went in with a Fluke Scopemeter, VERY clear harmonics while equipment in operation. I turned off 1 disconnect/panel at a time, until harmonics went away. I then unplugged the offending piece of customer equipment. All the while taking snapshots of waveform with O-scope (Fluke has feature to do this internally and export via a PC later). We then informed customer to not reconnect that equipment until it was repaired or we would disconnect the 150kva service. Harsh but the service equipment was several hundred thousand dollars and 8-12 months lead time for replacements.