Assign new values to modify voltage type, all of the unit are volt. 
   Namespace:   Autodesk.Revit.DB.Electrical  
  Assembly:   RevitAPI  (in RevitAPI.dll) Version: 2015.0.0.0 (2015.0.0.0) 
Syntax
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Parameters
- actualValue
 -  Type:  System Double  
 
- minValue
 -  Type:  System Double  
 
- maxValue
 -  Type:  System Double  
 
Exceptions
| Exception | Condition | 
|---|---|
| Autodesk.Revit.Exceptions ArgumentException | Actual value can't be more than minValue or less than maxValue, and all of them can't be negative, otherwise the exception will be thrown. |