Nrtl Listing; Nfpa 79 - Siemens SINUMERIK Series Function Manual

Standards and specifications
9.3 Machine safety in the USA
9.3.3

NRTL listing

To protect employees, all electrical equipment used in the USA must be certified for the planned
application by a "Nationally Recognized Testing Laboratory" (NRTL) certified by the OSHA.
NRTLs are authorized to certify equipment and material by means of listing, labeling, or similar.
Domestic standards (e.g. NFPA 79) and international standards (e.g. IEC/EN 61508 for E/E/
PES systems) are the basis for testing.
9.3.4

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
– Offer the same level of protection as hard-wired controllers
– Be implemented in accordance with a recognized standard that defines the requirements
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.
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(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
for such systems.
Function Manual, 10/2015, 6FC5397-3EP40-5BA3
Safety Integrated