Electrical Standard for Industrial Machinery
Errata No.: 79-07-1
The Technical Committee on Electrical Equipment of Industrial Machinery notes the following errors in the
2007 edition of NFPA 79, Electrical Standard for Industrial Machinery.
1. Page 79-6, opening paragraph four, beginning with “A reference in brackets [ ] following a section”: Change “Annex
H” to “Annex I.” Also on page 79-6, in opening paragraph five, beginning with “Information on referenced publications”:
Change “Annex H” to “Annex I.”
2. Page 79-15, subsection 5.5.4, item (2): Insert missing ending quotation mark after the word “disconnect,” to read as
(2) A manual motor controller marked “suitable as motor disconnect” and compliant with UL 508 where located
on the load side of the last short-circuit protective device (in the branch)
3. Page 79-15: paragraph 220.127.116.11, Exception, second sentence: Change “can be” to “are capable of being,” to read as
Exception: In the absence of a rated enclosure, the determination of the suitability of an enclosure as protection
from electrical shock shall be determined by using a test finger as described in Figure 18.104.22.168. The test finger shall
be applied, with only minimal force, in every opening in the enclosure after removal of all parts of the enclosure
that are capable of being removed without the use of a tool. The test finger shall not encounter live parts in any
4. Page 79-15: Insert missing paragraph 22.214.171.124 (with editorial change of “When” to “Where”), to read as follows:
126.96.36.199 Where provided with a defeat mechanism as permitted in 188.8.131.52, live parts mounted on the inside of doors
that are operating at over 50 volts shall be protected from unintentional direct contact by the inherent design of
components or the application of barriers or obstacles such that a 50 mm (2 in.) sphere cannot contact any of the
live parts in question.
5. Page 79-17, paragraph 184.108.40.206, item (2): Change “overcorrect” to “overcurrent.”
6. Page 79-81: Annex I, Minimizing the Probability of Control Function Failure, from the 2002 edition was mistakenly
omitted from the 2007 edition. For the 2007 edition, Annex H should be Minimizing the Probability of Control Function
Failure, and the current 2007 Annex H, Informational References, should be Annex I.
Annex H is herewith included in its entirety.
7. Pages 79-81 and 79-82: Change all paragraph numbers in Annex I, Informational References, from H.1, H.2, H.3, etc.,
to I.1, I.2, I.3, etc.
(grounded) side of the control supply (see
(3) Stopping by de-energizing (see 9.2.2)
(4) Switching of all live conductors to the device
Annex H Minimizing the Probability of Control (5) Use of switching devices having positive
Function Failure opening operation (see IEC 60947-5-1)
This annex is not a part of the requirements of this NFPA (6) Circuit design to reduce the possibility of
document but is included for informational purposes failures causing undesirable operations
H.3 Provisions for Redundancy.
H.1 The following discussion is explanatory material H.3.1 By providing partial or complete redundancy it is
on 9.4.1 General Requirements and 220.127.116.11. possible to minimize the probability that one single
H.1.1 The measures, and the extent to which they are failure in the electrical circuit can result in a hazardous
implemented, either individually or in combination, condition. Redundancy can be effective in normal
depend on the safety requirements associated with the operation (i.e., on-line redundancy) or designed as
respective application. special circuits that take over the protective function (i.e.,
H.1.2 General. off-line redundancy) only where the operating function
H.1.2.1 Measures to reduce these risks include, but are
not limited to, the following: H.3.2 Where off-line redundancy that is not active
during normal operation is used, suitable measures
(1) Protective devices on the machine (e.g., should be taken to ensure that these control circuits are
interlock guards, trip devices) available when required.
(2) Protective interlocking of the electrical circuit H.4 Use of Diversity.
(3) Use of proven circuit techniques and The use of control circuits having different principles of
components (see H.2) operation or differing types of devices can reduce the
(4) Provisions of partial or complete redundancy probability of faults and failures giving rise to hazards.
(see H.3) or diversity (see H.4) Examples include the following:
(5) Provision for functional tests (see H.5) (1) The combination of normally open and
H.1.2.2 In general, only single failures are to be normally closed contacts operated by
regarded. In the event of higher levels of risk, it can be interlocking guards.
necessary to ensure that more than one failure cannot (2) The use of different types of control circuit
result in a hazardous condition. components in the circuit.
(3) The combination of electromechanical and
H.2 Measures to Minimize Risk in the Event of
electronic circuits in redundant configurations.
(4) The combination of electrical and
Use of proven circuit techniques and components
nonelectrical systems (e.g., mechanical,
measures to minimize risk in the event of failure include
hydraulic, pneumatic) can perform the
the use of proven circuit techniques and components.
redundant function and provide the diversity.
These measures include, but are not limited to, the
(1) Bonding of control circuits for operational
purposes (see 18.104.22.168) H.5 Functional Tests.
(2) One terminal of the control device (i.e., the Functional tests can be carried out automatically by the
operating coil) connected to the bonded control system, or manually by inspection or tests at
conductor and all switching elements (e.g., start-up and at predetermined intervals, or a combination
contacts) connected to the non-earthed as appropriate (see also Sections 17.2 and 18.6 ).
Issue Date: November 16, 2006
Copyright © 2006 All Rights Reserved
NATIONAL FIRE PROTECTION ASSOCIATION
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