A 'person conducting a business or undertaking' (PCBU) is a legal term under WHS laws for individuals, businesses or organisations that are conducting business. A person who performs work for a PCBU is considered a worker.
An RCD (residual current device), also called a safety switch, is a life-saving device which is designed to prevent you from getting electrocuted. The RCD monitors the electric current between the Active and the Neutral wire and should be the same in the opposite directions. If it detects a difference more than (for example) 30mA, the RCD trips. The difference can be caused by a person touching live parts, through moisture leaking to the earth, ...
The term transportable structure includes both vehicles and structures with or without wheels that can readily be moved from one site to another under their own motive power or by some other means. This includes temporary site offices, cloakrooms, meeting offices, dormitories, canteens, toilets, workshops, site huts or other facilities provided on construction and demolition sites.