In Database environment, set following database parameter as sysdba:

ALTER SYSTEM SET log_archive_format=’arch_%t_%s_%r.arc’ SCOPE=spfile;
ALTER SYSTEM SET log_archive_dest_1=’location=/u01/oradata/MYSID/archive/’ SCOPE=spfile;

In Grid environment, stop the entire clustered database by following command as oracle user.
$ srvctl stop database -d SID
Note:
By above command, database will be shutdown.
SID: Global database name.

In Database environment, issue the following command to enable archive log mode:
STARTUP MOUNT;
ALTER DATABASE ARCHIVELOG;
SHUTDOWN IMMEDIATE;

In Grid environment, start the entire clustered database by following command as oracle user:
$ srvctl start database -d MYSID
By above method you will alter your RAC database to archive log mode.
************************************************************************

Note: Please don’t hesitate to revert in case of any query OR feedback.

Thanking you.

Have a easy life ahead.