Technical data

Safety Integrated Functions
8.1 Standards and regulations
Function Manual
Function Manual, 06/2012, 6SL3097-4AB10-0BP4
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8.1.3.3 NFPA 79
Standard NFPA 79 (Electrical Standard for Industrial Machinery) applies to electrical
equipment on industrial machines with rated voltages of less than 600 V. A group of
machines that operate together in a coordinated fashion is also considered to be one
machine.
For programmable electronics and communication buses, NFPA 79 states as a basic
requirement that these must be listed if they are to be used to implement and execute safety-
related functions. If this requirement is fulfilled, then electronic controls and communication
buses can also be used for Emergency Stop functions, Stop Categories 0 and 1 (refer to
NFPA 79 9.2.5.4.1.4). Like EN 60204-1, NFPA 79 no longer specifies that the electrical
energy must be disconnected by electromechanical means for emergency stop functions.
The core requirements regarding programmable electronics and communication buses are:
system requirements (see NFPA 79 9.4.3)
1. Control systems that contain software-based controllers must:
– In the event of a single fault
(a) cause the system to switch to a safe shutdown mode
(b) prevent the system from restarting until the fault has been rectified
(c) prevent an unexpected restart
– Offer the same level of protection as hard-wired controllers
– Be implemented in accordance with a recognized standard that defines the
requirements for such systems.
2. IEC 61508, IEC 62061, ISO 13849-1, ISO 13849-2 and IEC 61800-5-2 are specified as
suitable standards in a note.
Underwriter Laboratories Inc. (UL) has defined a special category for "Programmable Safety
Controllers" for implementing this requirement (code NRGF). This category covers control
devices that contain software and are designed for use in safety-related functions.
A precise description of the category and a list of devices that fulfill this requirement can be
found on the Internet at the following address:
http://www.ul.com → certifications directory → UL Category code/ Guide information → search
for category "NRGF"
TUV Rheinland of North America, Inc. is also an NRTL for these applications.