Using the Revit API, if the voltage of a connector is set using an instance parameter, when an ElectricalSystem is created using it the voltage is set to 0. The ElectricalSystem then cannot be connected to a panel.
More details about this error are available at this forum thread:
https://forums.autodesk.com/t5/revit-api-forum/newelectricalsystem-specify-voltage-amp-poles/td-p/62...
This error has been logged as issue REVIT-180706 [API ElectricalSystem.Create() cannot specify voltage and poles].
Fix this error so that the API can be used to automate what is possible using the standard Revit UI.