Surge Protective Device for machines
The Electrical Standard for Industrial Machinery NFPA 79 is the relevant safety standard published by the USA's National Fire Protection Association (NFPA). It sets essential electrical safety requirements for industrial machinery. Every industrial machine that is produced in or imported into the USA has to fulfil this requirements. If not, it is prohibited from being connected to the mains supply. NFPA 79, § 7.8.1 states that " SPD's (surge protective device) shall be provided for industrial machinery with safety interlock circuits to protect against the effects of over-voltages due to lightning and switching surges." Important to know is that the stated short-circuit current of the SPDs should not exceed the short-circuit current rating required at the installation location. UL Standard UL 1449 describes where SPDs should be installed using the type classification. This should not be mistaken with IEC type classification, which describes the device performance. As the voltage level and ground configuration of the mains supply can vary, the correct surge protection device need to be selected e.g. to match WYE or corner grounded DELTA.