Can not connect to an external DB

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I need to read some data from an external DB in some of my custom blocks, but when I ask to concrete5 to connect to my 2nd DB, he just ignore me:

$db = Loader::db();
$db = Loader::db( 'server2', 'user2', 'pass2', 'db2', true);         
$fts = $db->Execute('SELECT * FROM table2');


He attempt to run the query but connected to de main DB.

I know this code is from version 5.6, I tried to find son reference for 5.7 but with no luck.

Thanks for your help, I am now desperate.