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NFPA 79, the Electrical Standard for Industrial Machinery

2002 edition, is scheduled to be published in October

2002. During this past cycle, NFPA 79 has undergone a

major overhaul in an effort to harmonize requirements with

those of IEC 60204. This, as you can imagine, was a

major undertaking and resulted in a heavy workload. The

work pioneered by the NFPA 79 technical committee has

provided a benchmark for future harmonization efforts.

This article will discuss the harmonization process that

took place and resulting changes to the NFPA 79 stan-

dard. In addition, significant changes that occurred dur-

ing the 2002 cycle will be discussed individually.

Update on NFPA 79, 2002by Tom Garvey and Todd Lottmann

www.iaei.org SEPTEMBER/OCTOBER 2002 81

UPDATE ON NFPA 79

Harmonization—Historical BackgroundIn March 1998, the NFPA 79 committee prepared astatement of work. The major elements of the state-ment of work are:

Harmonization—PurposeAs the users and the manufacturers of industrial ma-chines move toward a global manufacturing com-munity, the need for a harmonized standard affect-ing industrial machinery becomes an economic ne-cessity. Generally, large users and manufacturers findregulations burdensome. However, multiple regu-lations as well as conflicting regulations are an eco-nomic disincentive to global expansion. In order toease the burden of differing regulation, and at thesame time maintain the high standard of electricalmachine safety, the NFPA 79 committee has ex-pressed their desire, through balloted vote, to har-monize NFPA 79 with IEC 60204-1.

Importance of Issue—HarmonizationToday’s industrial machines are very complex andexpensive. As manufacturing lines become modularand transportable, industrial machines originally

produced for a foreign market may quickly be trans-ported to the domestic market. The reverse is alsotrue. Differing electrical standards add a large costto multinational manufacturers as they build, andsometimes move, manufacturing facilities.

Harmonization—ObjectiveThis work is necessary to accomplish the goal of al-lowing industry to economically build one indus-trial machine capable of passing a detailed electri-cal safety inspection using either IEC 60204-1 orNFPA 79 standard. Both the NEC Technical Corre-lating Committee (TCC) and the Standards Councilreviewed the statement of work in July 1998. TheTCC unanimously recommended the following actionto the Standards Council:

“The Technical Correlating Committee agrees withthe efforts of the NFPA 79 committee to harmonizethe technical requirements of NFPA 79 and IEC60204, where feasible and where in concert with theNEC and its related codes and standards”

ResultThe NFPA Standards Council considered and con-

NFPA 79 Document Form Change SummaryNFPA 79 – 1997 Chapter Title/Topic NFPA 79 – 2002

1 Scope and Purpose 1

2 Referenced Publications 2

3 Definitions 3

5 General Operating Conditions 4

7 Supply Circuit Disconnect and Termination 5

6 Protection of Personnel 6

8 Overcurrent Protection 7

19 Grounding 8

9 Control Circuits and Functions 9

13 Operator Interface and Control Devices 10

20 Electronic Equipment 11

11 Control Equipment: location, mounting, and enclosures 12

15 Conductors, Cables, and Flexible Cords 13

16 & 17 Wiring Practices 14

18 Electric Motors and Associated Equipment 15

14 Accessories and Lighting 16

4 Marking, Warning Signs and Reference Designations 17

4 Technical Documentation 18

- Testing and Verification 19

Table 1. NFPA 79 Document Form Change Summary

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curred with the recommendation. In June 1999, theNFPA 79 committee formed 20 task groups. Each taskgroup was assigned one proposed new clause. Thetask group compared NFPA 79–1997, Clause X withIEC 60204-1 Clause X. The task group presented itswork to the entire committee on several occasionsfor review and comment. The task group chair thensubmitted the work as a proposal to amend NFPA79–1997.

Changes Resulting from Harmonization EffortOne of the major revisions that occurred as a resultof harmonization was the reorganization of the docu-ment chapters to match the IEC 60204 layout. Theintent was to increase the usability of the documentand align similar requirements. As a result, the ma-jority of the clauses in the 1997 edition of NFPA 79have moved to align with IEC 60204. Table 1 (previ-ous page) provides a summary of the chapter relo-cations.

Highlight and Analysis of Significant ChangesSignificant changes, in addition to the changes result-ing from harmonization, occurred during the past cycle.Many of the changes were editorial to update the docu-ment to comply with the NFPA Manual of Style. How-ever, some significant technical changes occurred inthe NFPA 79 standard this past cycle. An overview ofthe significant changes is provided here:

Chapter 4: General Operating Conditions.Chapter 4, specifically 4.3.1 and 4.4.1, was revised toclarify the allowance for operation of electrical equip-ment outside those conditions specified in chapter 4with the use of an agreement between the user andsupplier. A note, referencing Annex B, was added. Thenew Annex B contains a sample inquiry form, whichcan be supplied by the user to provide the supplier ofthe machinery sufficient information for the proper de-sign, application, and utilization of the electrical equip-ment of the machine.

5.3.3.1 Supply Circuit DisconnectingMeans Requirements.New requirements for supply circuit disconnectingmeans were added in section 5.3.3.1(3) & (5) andstate:

“5.3.3.1 Requirements…(3) Be provided with apermanent means permitting it to be locked in theoff (open) position only (e.g., by padlocks) inde-pendent of the door position. When so locked, re-mote as well as local closing shall be prevented.…(5)Be operable, by qualified persons, independent ofthe door position without the use of accessory toolsor devices.”

These new requirements pertain to devices usedas the supply circuit disconnecting means, whichutilize a door-mounted handle. The new require-ments mandate the use of an internal, permanentlylockable handle in addition to the external door-mounted handle (see photo 1). These requirementswere added to cover a safety concern with loss ofcontrol of the disconnecting means operatingmechanism when the door is opened and the exter-nal handle swings away. The added requirementsprovide a solution to this concern while allowingthe use of these disconnects.

7.2.1 Overcurrent Protection—General.A new sentence and note were added to the generalovercurrent protection requirements regarding theproper use of overcurrent protective devices. Thenew sentence states:

“7.2.1 General. Supplementary overcurrent pro-tective devicesshall not be usedas a substitute forbranch circuitovercurrent pro-tective devices…”

This clarifiesthat branch-cir-cuit overcurrentprotection is re-quired for protec-tion of industrialmachinery cir-cuits. Theses u p p l e m e n t a lovercurrent pro-tective devicesare not suitablefor branch-circuitprotection andcannot be used

UPDATE ON NFPA 79

Photo 1. Example of internal, permanently lockable handle.

Photo 2. Examples of branch circuit andsupplementary fuses.

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for this purpose. Supplementalovercurrent devices are intendedto be used as a component of anend product. They are offered in awide variety of performance char-acteristics, voltage ratings, and in-terrupting ratings; and, therefore,each supplemental overcurrentprotective device is only allowed tobe used under specific conditions.The use of supplementalovercurrent protective devices inreplacement of branch-circuit pro-tection creates an unsafe installa-tion. Accompanying the new sen-tence was the addition of a note inAnnex A. Note A.7.2.1, providesbackground information and a listof different types of supplementalovercurrent protective devices andhow to identify them.

“How can I tell if a device is a branch-circuitovercurrent protective device?”

Review of the device labeling will be required toassure the proper device is being used to providebranch-circuit protection. NEC 240.6 provides a listof devices which are suitable for protection of branchcircuits. This includes inverse time circuit breakersand fuses. In addition, NEC 430.52 provides a list ofdevices which are suitable for short-circuit andground-fault protection of motor branch circuits.Fuses suitable for branch-circuit protection includeClasses L, R, J, T, CC, G, H, K5, and plug fuses. Popu-lar supplementary fuses include midget, glass tube,and miniature types (see photo 2).

Circuit breakers suitable for branch-circuit pro-tection will be listed and marked circuit breaker.Supplemental protectors, often referred to as minicircuit breakers, are recognized components ratherthan listed devices (see photo 3).

9.2.4 Overriding Safeguards.A new requirement was added for control circuitsused in the suspension of a safeguard. The require-ment states:

“9.2.4 Overriding Safeguards. The control circuitfor the suspension of a safeguard shall have the samesafety requirements as the suspended safeguard it-self.”

A system fault in the suspension of the safeguardcan lead to hazardous conditions. Therefore, thecontrol circuit for the suspension of a safeguard mustbe treated like the suspended device itself to pro-vide the same level of safety as the safeguard itself.

9.3.6 Protective Interlock.This section was revised to clarify the types ofswitches allowed for use in protective interlock cir-cuits. The new requirement states:

“9.3.6 Protective Interlock. Where doors or guardshave interlocked switches used in circuits with safety-related functions, the interlocking devices shall belisted safety switches, have either positive (direct)opening operation or provide similar reliability andprevent the operation of the equipment when thedoors are open (difficult to defeat or bypass).”

The term listed safety switch was added to re-strict devices, such as limit switches, which are eas-ily defeatable. Listed safety switches, as required in9.3.6, refer to switches used in door and guard in-terlock circuits which are listed for this purpose andnot easily defeatable. Concern over the new word-ing listed safety switches was voiced through pub-lic comments received during the Report On Com-ments (ROC) phase of the cycle. The committeevoiced its intent that the new wording is not in-tended to require UL 98 fusible and nonfusibleswitches, which are commonly referred to in the in-dustry as “safety switches.” The desired level of per-formance requirements, positive-opening contacts,for these listed safety switches were added to clarifythe intent of this requirement.

9.4.3 Control Systems Incorporating Software andFirmware Based Controllers.This is a new requirement for control systems incorpo-rating software and firmware based controllers. Theorigin of this requirement is IEC 60204. This section

Photo 3. Listed circuit breaker and supplemental protector.Photo courtesy of Square D/Schneider Electric

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relocated from 11.3.4 during the comment stage toseparate the system requirements, which are appropri-ate in Chapter 9, from the component requirements,which are appropriate in Chapter 11. The requirementis as follows:

“9.4.3 Control Systems Incorporating Software andFirmware Based Controllers. Control systems incor-porating software and firmware based controllersperforming safety-related functions shall:

(1) In the event of any single failure perform as follows:a. Lead to the shutdown of the system in a safe stateb.Prevent subsequent operation until the compo-

nent failure has been correctedc. Prevent unintended startup of equipment upon

correction of the failure,(2) Provide protection equivalent to that of control

systems incorporating hardwired/hardware compo-nents, and

(3) Be designed in conformance with an approvedstandard that provides requirements for such systems.”

This change provides a list of requirements forcontrol systems incorporating software and firmwarebased controllers. In addition, this section now re-quires compliance with an appropriate applicationstandard. Note A.9.4.3 provides a link to IEC 61508which provides requirements for this control systemdesign.

11.3.4 Programmable Equipment—Use in Safety-related Functions.This is a new requirement for programmable equip-ment used in safety-related functions. The origin of thisrequirement is IEC 60204.The new requirement reads:

“11.3.4 Use in Safety-Related Functions. Softwareand firmware-based controllers to be used in safety-related functions shall be listed for such use.”

This section was revised to require listing of soft-ware and firmware based controllers used in safety-related functions.

Table 13.5 Conductor Ampacity.Allowable ampacity of conductors in Table 13.5 wasrevised from Table 4 NFPA 79–1997. The revision re-moved the fourth column in Table 4, titled “ControlEnclosure,” which contained ampacities from the firstcolumn in NEC Table 310.17 for conductors in openair. This change now restricts application of conduc-tors to ampacities similar to the 75°C column in NECTable 310.16. The reason for the change relates tothe fact that nearly all devices are now rated for con-nection to 75°C conductors applied at ampacities inNEC Table 310.16.

13.5.2 Ampacity Adjustment.This section contains a new requirement clarifyingproper ampacity adjustment for 90°C insulated con-ductors used on industrial machinery. The new re-quirement states:

“13.5.2 Ampacity adjustment for 90 degree C in-sulated conductors ampacities shall be based uponthe ampacities in the 75 degree C column of Table13.5.”

This requires 75°C ampacities to be used forampacity adjustments for 90°C insulated conductors.

13.6.1 Conductor Sizing. A significant change to NFPA 79 is revision to 13.6.1permitting the use of 16 and 18 AWG conductors insmall branch-circuit applications. The change keeps14 AWG as the minimum recommended conductorsize with the allowance for the use of 16 and 18 AWGconductors under the specified conditions. A sampleof 13.6.1 is shown here:

“13.6.1 Conductors shall not be smaller than 14 AWG forpower circuits unless otherwise permitted in (a) or (b).

(a) 16 AWG shall be permitted, if part of a jacketedmulticonductor cable assembly or flexible cord, or in-dividual conductors used in a cabinet or enclosure,under the following conditions:

(1) Non-motor power circuits of 8 amperes or lessprovided all the following conditions are met:

(a) Circuit is protected in accordance withClause 7

(b) Overcurrent protection does not exceed 10amperes

(c) Overcurrent protection is provided by oneof the following:

(1) A branch circuit rated circuit breakerlisted and marked for use with 16 AWG wire

(2) Branch circuit rated fuses listed andmarked for use with 16 AWG wire

(3) Class CC, Class J, or Class T fuses…”

Notice this allowance is limited to certain require-ments including: limited ampacity circuits, specificovercurrent protective devices, and limits for exposureto physical damage. An extensive investigation includ-ing engineering analysis and laboratory testing wereused to substantiate the change.

14.1.4 Cables.Several new sections were developed to recognize andregulate the use of cables. The type, size, and ampacityof the cable assembly are determined by applying therequirements of Clause 13. Clause 14 is intended toensure that cables are installed in such a manner to

UPDATE ON NFPA 79

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minimize the potential for physical damage. Anothernew section, 14.5.11, specifically recognizes the usesof cable tray as a support method.

16.1.2 Receptacles.Worker safety is enhanced through a new require-ment that applies to maintenance receptacles.

“16.1.2 Receptacles, which are part of the indus-trial machine, either external or internal to the con-trol cabinet and intended for use by maintenancepersonnel, shall have ground-fault circuit-interrupterprotection for personnel.”

In addition, Section 16.1.2 requires that worklights be protected by Class A type ground-fault cir-cuit interrupter if used in wet locations.

19.1 Testing and Verification—General.This important new clause requires testing to en-sure that the machine has an effective ground-faultcurrent path. Industrial machines are permitted toutilize the machine frame as an equipment ground-ing conductor. Typically, all tests will be done in thefactory. However, if the machine is manufactured insections and assembled on the site, the continuityof the equipment grounding conductor will be veri-fied after assembly. Section 19.2 stipulates that oneof the two proscribed test methods shall be used toverify equipment-grounding continuity. In addition,re-testing is required by Section 19.7 on portions ofa machine that have been changed or modified.

Tom wishes to thank the chair of NFPA 79, Mike Callanan, andthe NFPA 79 staff liaison, Joe Sheehan. The successful completionof this project is founded on your energy, patience, and expertguidance.

Tom Garvey inspects for the state of Wisconsin. He repre-sents the International Association of Electrical Inspectors onCode Making Panel-11 for the National Electrical Code. He isthe IAEI representative on NFPA 79, The Electrical Standardfor Industrial Machinery. The global companies that makeup Wisconsin’s industrial base gives Tom frequent opportuni-ties to view a variety of attempts in harmonizing the electri-cal wiring of industrial machinery to the NEC market.

Todd Lottmann is an engineer for Cooper Bussmannfocusing on electrical codes and standards. He serves asan alternate member of NEC Code Making Panel-12 rep-resenting the National Electrical Manufacturers Associa-tion. He is a nationally known authority on overcurrentprotection techniques. Todd was of great help to the NFPA79 committee during critical stages of the harmoniza-tion project. Todd can be often found at IAEI Sectionand Chapter meetings. His seminars on electrical safetyand overcurrent protection are interesting, informative,and often very entertaining.