Special Restricted Plumbing & Heating (SP-PH) Classification: shall be permitted to install, maintain or repair electric wiring or devices only as an incident to the licensee’s plumbing, heating or air conditioning business. Furthermore, the license authorizes the licensee to install, maintain or repair only wiring that is directly related to plumbing, heating or air conditioning equipment that: (1)is restricted to circuits or parts of a circuits that operate at voltage not exceeding 600 volts, phase to phase; (2)that is electrically isolated from the building wiring system by an overcurrent protective isolating devise, such as a fused switch or circuit breaker, that; (a) has been installed, complete with line-side connectors, by others.