New Language in the 2012 NFPA 70E clarifies the importance of one line diagrams for verifying the proper sources of energy are being isolated:
•120.2(F)(1)(a): Revised by indicating that the employer is responsible for providing an effective means for locating “all” sources of energy when up-to-date drawings are not available.
Locating Sources. Up-to-date single-line drawings shall be considered a primary reference source for such information. When up-to-date drawings are not available, the employer shall be responsible for ensuring that an equally effective means of locating all sources of energy is employed.