I have automated scripts that load features into a geometric network. I use the Append (Data Management)—ArcMap | Documentation (arcgis.com) tool to load features. You would likely need to open an edit session on the target database for this, as well. Example below.
One thing to note - I found that the append method works well if loading less than 10,000 features. Once you get over this, it would really slow down. So, if you have a lot of features, you may want to break them up into subsets of 10,000 features and perform an append of each subset into the network.
with arcpy.da.Editor(target_db_conx_file) as edit:
script.logger.info('Appending new meters to target feature class: ' + target_meters_fc)
arcpy.management.Append(inputs=new_meters_fc, target=target_meters_fc, schema_type='NO_TEST')
script.logger.info('Successfully appended new meters to target feature class: ' + target_meters_fc)
