Reason for Credential: Except as provided under s. 145.06 (4) Stats., and pursuant to s. 145.06, Stats., no person may install plumbing unless the person holds a credential issued by the department as a licensed master plumber, licensed master plumber restricted, licensed journeyman plumber, licensed journeyman plumber-restricted, registered plumbing apprentice, registered plumbing learner-restricted, registered utility contractor or registered pipe layer.Requirements of Credential: Pursuant to s. 145.14, Stats., the plumbing activities that may be undertaken by a person who holds a credential as a licensed master plumber-restricted service, licensed journeyman plumber-restricted service or a registered plumbing learner-restricted service shall be limited to the installation or modification of all of the following:- Privately owned wastewater treatment systems and components under ch. Comm 83.- Building sewers and private interceptor main sewers under ch. Comm 82.- Water services and private water mains under ch. Comm 82.A person who holds the credential shall carry on his or her person the credential issued by the department while performing or conducting the activity or activities permitted under the credential.The plumbing activities that may be undertaken by a person who holds a credential as a registered learner-restricted service shall be performed under the direct supervision of a person who holds a master plumber license, a master plumber-restricted service license, a journeyman plumber license or a journeyman plumber-restricted service license. A business engaged in the installation of plumbing that utilizes plumbing learners shall maintain a ratio of at least one journeyman plumber or journeyman plumber-restricted for each plumbing learner. For this purpose, a master plumber or master plumber-restricted may act as a journeyman plumber or journeyman plumber-restricted, respectively.Qualifications for Credential: A person applying for a plumbing learner-restricted service registration to install or modify plumbing shall be at least 16 years old and shall have completed the 12th grade in school or its equivalent.