private const string ExampleConString = ConfigurationManager.ConnectionStrings["Example"].ConnectionString;

public class ConnectionStringEncapsulator
{
    private string connectionString = ConfigurationManager.ConnectionStrings["Example"].ConnectionString; //global connection string
    public string connectionString { get; }
}

 public class TradeDB
{
    private ConnectionStringEncapsulator TradeDBconnectionString;
    public TradeDB()
    {
        TradeDBconnectionString = new ConnectionStringEncapsulator();
    }
}

private readonly string TradeDBconnectionString;