Accessing Entity Framework from Timer Job: connection string problem

I had a DB that normally I access from my SharePoint (2010) custom feature by Entity Framework. The connection string is stored in the web.config.

If I do something like that from outside TimerJob:

using (DB db = new DB()) { }

I get a working instance, if I do the same thing from TimerJob I get exception. To avoid this I stored a connection string into my "Configuration List" so that my code now is:

string cs = //GET STRING FROM LIST
using (DB db = new DB(cs)) { }

but this generates me an exception.

Where is the problem?

I tried with these connection string: metadata=res:///NewDB.csdl|res:///NewDB.ssdl|res://*/NewDB.msl;provider=System.Data.SqlClient;provider connection string='Data Source=.;Initial Catalog=CNH_MW;Integrated Security=True;MultipleActiveResultSets=True;Application Name=EntityFramework'

OR

metadata=res:///NewDB.csdl|res:///NewDB.ssdl|res://*/NewDB.msl;provider=System.Data.SqlClient;provider connection string="Data Source=.;Initial Catalog=CNH_MW;Integrated Security=True;MultipleActiveResultSets=True;Application Name=EntityFramework"

without any success..

Exception: The specified named connection is either not found in the configuration, not intended to be used with the EntityClient provider, or not valid
Stacktrace:    at System.Data.EntityClient.EntityConnection.ChangeConnectionString(String newConnectionString) 

at System.Data.Objects.ObjectContext..ctor(String connectionString, String defaultContainerName) at CNH.WorkFlowManufacturing.CNH_MW..ctor() at CNH.WorkFlowManufacturing.DBHandler.get_GetCNH_MW() at CNH.WorkFlowManufacturing.JobImportazione.ImportaFile(SPFile file, SqlConnection& conn, Int32 PK_LOG) at CNH.WorkFlowManufacturing.JobImportazione.Execute(Guid targetInstanceId)

Any suggestion? Thank you very much!