Md. Code, Public Utilities § 6–202

(a) The Commission may classify the public service companies under its jurisdiction.

(b) Two public service companies are of the same class, if they are both:

(1) common carrier companies;

(2) electric companies;

(3) gas companies;

(4) gas and electric companies;

(5) sewage disposal companies;

(6) telegraph companies;

(7) telephone companies; or

(8) water companies.