In the United States, an electrician specialized in the installation of electrical systems is required to follow the National Electrical Code and follow all local legislation regulating the installation of electrical systems. Failure to do so might cost an  electrician  his license. The regulations will change depending on the state and depending on the setting. A factory will for instance, have different codes to follow from a private residence. These regulations are quite important for ensuring safety and good service quality. Safety would be a much iffier thing were it not for these codes.