Redundancy 15 : The application of more than one device or system, or part of a device or system, with the objective of ensuring that in the event of one failing to perform its function another is available to perform that function
NFPA 79 Electrical Standard for Industrial Machinery, 2002 ed. http://www.nfpa.org/assets/files/AboutTheCodes/79/ 79-A2002-rop.pdf, (Electr Std for Ind Machinery - Amer) {225 NFC}