Conformity Magazine

See this article in our Digital Edition
Download a pdf of this article (right click to save the pdf)

Many machine tools are manufactured and placed into service in the United States. Unfortunately, many of these machines are placed into service without meeting the legally required safety approvals for industrial machinery. In great measure, this is due to the fragmented system of enforcement which characterizes the machinery safety field in the U.S. However, it is also due to the presence in the United States of NRTL-approved “panel shops.” Many enforcement authorities, manufacturers, and users of machinery misunderstand a panel shop approval, and therefore fail to enforce the overall machinery safety requirements.

Legal Requirements for Machinery Approval by an NRTL
Legal requirements for machinery begin at the federal level. The Occupational Safety and Health Administration (OSHA, the federal agency responsible for regulating machinery used in the workplace) has defined types of products that require evaluation to published safety standards in order to be legally used in U.S. workplaces. OSHA defines types of equipment that require approval by an NRTL (Nationally Recognized Testing Laboratory)¹. This list includes electrical conductors or equipment². All machine tools that are electrical equipment (e.g., they receive electrical power or generate electrical power for on-board use) are thus included, and require approval by an NRTL.

State workplace safety agencies, as well as county, and municipal authorities, typically follow OSHA requirement by requiring electrical products to be approved before the product may be used in workplaces within the jurisdiction. These authorities, who enforce safety requirements for specific locations, are referred to as AHJs (authorities having jurisdiction).

The AHJ commonly looks to the National Electrical Code (NEC, published as the standard NFPA-70) for guidance on how to enforce NRTL approval requirements. The NEC, in article 100, defines an approved product as “acceptable to the authority having jurisdiction.” In light of the requirement by OSHA at the federal level, NRTL approval is the basis of acceptance by the AHJ.

The NEC also defines how an AHJ may recognize that a particular piece of equipment has been approved by an NRTL. The NEC defines two methods of identification, “listed” and “labeled.” Listed is defined, in the NEC article 100, as:

“Equipment, materials, or services included in a list published by an organization that is acceptable to the authority having jurisdiction and concerned with evaluation of products or services, that maintains periodic inspection of production of listed equipment or materials or periodic evaluation of services, and whose listing states that the equipment, material, or services either meets appropriate designated standards or has been tested and found suitable for a specified purpose.”

What this means is that a product is “listed” if a NRTL tests and approves a product as meeting published safety standards, performs periodic reviews of the compliance of continuing production, and then lists that approval in a publication by the NRTL. In actual practice, the NRTL performs at least two follow-up inspections per year to verify continued compliance with the safety requirements, and the publication of listed products is commonly performed via the Internet.

The NEC also defines a method for labeling approved equipment. The NEC, in article 100, defines labeling as:

“Equipment or materials to which has been attached a label, symbol, or other identifying mark of an organization that is acceptable to the authority having jurisdiction and concerned with product evaluation, that maintains periodic inspection of production of labeled equipment or materials, and by whose labeling the manufacturer indicates compliance with appropriate standards or performance in a specified manner.”

This means that a product is “labeled” if a NRTL tests and approves a product as meeting published safety standards, performs periodic reviews of the compliance of continuing production, and then affixes on each approved product a mark indicating compliance. Again, in actual practice, the NRTL performs at least two follow-up inspections per year, and each product manufactured is marked with the NRTL’s trademarked listing symbol indicating compliance.

Often a product is both listed and labeled, that is, it is both listed in a publication (or online directory) and bears the NRTL listing mark.

The AHJ requires that products which connect to the electrical system or which have electrical power within them be listed or labeled. This requirement fulfills the requirements of the National Electrical Code, which most jurisdictions have adopted as a legal requirement in the jurisdiction. It also fulfills the requirements of OSHA for usage of machinery in the workplace.

Technical Standards for Machinery Approval
Machines that undergo a field evaluation process are assessed according to published technical standards. The definition of applicable standards follows a hierarchy. First, the standards defined by OSHA as applicable standards under the NRTL program should be applied. Since these standards are legally required by OSHA under U.S. statutory authority, they take precedent over all other technical standards. The list of standards required by OSHA for use by NRTLs in approving products is publicly accessible at this link.

After the OSHA required standards, the second most important source of defining applicable standards for equipment is the National Electrical Code. The NEC itself is always applicable. In addition, where specific requirements for products exist, the NEC defines product safety standards in Annex A, Product Safety Standards. This list of standards is informational, but it should be followed wherever possible.

Third, standards that are published by standards development organizations in the United States (such as the National Fire Protection Association (NFPA) or the American Society of Mechanical Engineers (ASME)), or standards which have been recognized by the American National Standards Institute (ANSI) should be followed if there is no directly applicable OSHA-recognized standard or no direct requirements in
the NEC.

Compendium of Common Standards for Machinery
Generically, all machines in the United States are assessed to two technical standards: ANSI/UL 508A, Industrial Control Panels, and ANSI/NFPA 79, Electrical Standard for Industrial Machinery. UL 508A, being an OSHA recognized standard, is the primary standard, and applies to all industrial control enclosures on the machine. The overall machine is assessed per ANSI/NFPA 79, which addresses wiring outside the machine enclosures, as well as machinery-related requirements such as interlocking devices, guarding, and so forth.

In addition, special requirements exist for special types of machines. These requirements are applied over and above the basic requirement for ANSI/UL 508A and NFPA 79 compliance. Examples of these requirements are the ANSI B11 series of standards for metal working machines, the ANSI B151 series of standards for injection molding machines, the ASME B20.1 and B30.13 standards for factory automation machinery, and the ANSI RIA R15.06 standard for industrial robots. When in doubt about the required standards for a particular machine, an NRTL should be consulted to help define the applicable standards and requirements.

Panel Shop Approval Programs
A panel shop program is a program whereby a machinery manufacturer can produce industrial control panels and place an NRTL panel shop approval mark on the completed control panel. These industrial control panels are approved per the technical standard UL 508A, Industrial Control Panels.

A panel shop approval is not the same as listing of the panel. During a listing examination, the NRTL directly examines the panel and approves the construction of the specific panel under consideration. That exact panel may then be produced by the manufacturer, with quarterly follow-up inspection of the panel manufacturing process to assure continued compliance with the standard.

Under a panel shop approval program, however, the NRTL may never directly inspect the approved panel. Instead, the panel shop performs a self-assessment of the panel and records basic information regarding the panel construction. On a quarterly basis, the NRTL inspects the panel shop, verifying proper record keeping and that documented procedures are being followed. Any panels currently in construction at the time of the inspection may also be spot-checked by the NRTL inspector.

The panel shop affixes a panel shop approval mark, which differs from NRTL to NRTL, inside the panel. This mark designates that the panel has been constructed to comply with the requirements of UL 508A, Industrial Control Panels, under a supervised panel shop program.

Figure 1: An NRTL panel shop approval from Underwriters Laboratories (UL, Underwriters Laboratories, and the depicted approval marks are trademarks of Underwriters Laboratories).

Panel Shop Approval and Machine Tools
Panel shop approvals for a panel apply only to the industrial control panel, not the entire machine for which the control panel is used. The technical standard, in the scope of the standard, states:

“These requirements cover industrial control panels intended for general industrial use, operating from a voltage of 600 volts or less. This equipment is intended for installation in ordinary locations, in accordance with the National Electrical Code, ANSI/NFPA 70, where the ambient temperature does not exceed 40°C (104°F) maximum.³”

In particular, the standard specifically states:

“An industrial control panel does not include an evaluation of the controlled equipment such as motors, heaters, lighting, and other loads connected to power circuits. Unless specifically noted on the wiring diagram of the industrial control panel, an industrial control panel does not include equipment mounted remotely from the panel and connected via a wiring systems or equipment field installed on or within the industrial control panel.⁴”

In addition, the standard states:

“An evaluation of the adequacy of the controls and protective devices contained in an industrial control panel for supervision and proper functioning of the controlled loads or equipment is not covered by the requirements in this standard. Such evaluations are covered by the standards applicable to the complete piece of utilization equipment.⁵”

All construction outside the industrial control panel is not examined, nor included in the industrial control panel approval. In particular, external loads (such as motors, heaters, and so on) are not examined. External control circuits, including safety-relevant circuits such as interlocking and emergency controls, are also not examined. Finally, the standard UL 508A includes within the standard no electrical safety tests.

An overall machine tool, therefore, cannot be considered approved merely by the presence of an industrial control panel approval. Such a control panel approval provides assurance that the internal construction of the control panel meets the requirements of UL 508A. However, the requirements of OSHA and the requirements of the National Electrical Code, remain unfulfilled.

NFPA 79 and Machinery Approvals
NFPA 79 is the applicable standard for overall machinery safety in the U.S. ANSI/NFPA 79, Electrical Standard for Industrial Machinery, is a compilation of the overall National Electrical Code (NEC) requirements for industrial machinery,
in particular article 670 on industrial machinery, but also various other relevant articles throughout the NEC.

NFPA 79 includes within its scope the complete machine, not just the electrical panels. The standard states:

“The provisions of this standard shall apply to the electrical/electronic equipment, apparatus, or systems of industrial machines operating from a nominal voltage of 600 volts or less, and commencing at the point of connection of the supply to the electrical equipment of the machine.⁶”

This means that when a machine is approved per NFPA 79 the machine then can be assumed to meet all the requirements of the National Electrical Code, as well as OSHA requirements for equipment used in the workplace. Therefore, only after the overall machine is approved to NFPA 79 should the AHJ for a particular jurisdiction find the equipment “acceptable for use” under the National Electrical Code.

Requirements of NFPA 79 for Machinery
NFPA 79 introduces numerous requirements for machinery that are not addressed in UL 508A. These requirements are critical for machinery safety and, as mentioned, are necessary elements of overall machinery safety in light of the National Electrical Code and OSHA requirements.

NFPA 79 requires constructional approval of the following critical areas:

Acceptable conditions of response to operating supply variation;
Physical environment and operating conditions of the machine;
Provisions for installation, handling, and storage of the machine;
Machinery disconnecting devices for supply and major assemblies;
Protection from electrical shock on the overall machine;
Grounding systems for safety, electrical function, and high-frequency interference on the overall machine;
Over-current and over-load requirements for machine loads (external to the control panel);
Safety interlocking, emergency stop, and emergency switching-off controls;
Overall machine controls and man/machine interface requirements;
Wiring practices outside the control panel;
Motor installation, connection to supply, and sizing requirements;
External conductor ampacity requirements;
Marking and safety signage on the machine;
User documentation and safety-relevant instructions.

In addition, it is only under NFPA 79 that electrical test requirements to ensure safety are required. The electrical tests for safety which NFPA 79 requires are:

Continuity testing of the machine safety grounding system;
Dielectric breakdown testing (hi pot) of the safety-relevant electrical insulation;
Electrical resistance of the safety-relevant insulation;
Functional testing of each safety interlock, e-stop, and emergency off control.

It is only after the overall machine has been assessed and approved per the requirements of NFPA 79 that the machine can be considered approved for use.

Conclusion
In conclusion, it is clear that the prevalence of panel shop program approvals can be misleading. Many AHJs, machinery manufacturers, and users assume that the presence of a panel shop approval in a machine control panel denotes that the machine meets the requirements of the National Electrical Code, and would be acceptable to OSHA for use in the workplace.

However, as has been demonstrated, the panel shop approval indicates that only the construction of the machine panel meets the constructional requirements of the standard UL 508A, Industrial Control Panels. The overall machine construction, including many elements which are critical for safety, such as electrical protection of external loads or safety interlocking systems, have been unaddressed. The control panel constitutes a component with constructional approval in the overall machine, but the machine itself is unaddressed. In addition, the panel itself still requires electrical safety testing, which can only be performed with validity after the panel is installed in the machine and connected to external loads.

Therefore, it is not valid for AHJs to approve machines as meeting the requirements of the National Electrical Code based solely on a panel shop approval. The machine is not yet known to comply with the National Electrical Code, and the machine does not yet meet OSHA requirements for use in a workplace. Overall approval per NFPA 79 achieves the safety goal of the AHJ and of OSHA, and allows users of machines to operate them confident that an NRTL has assessed and approved the complete machine for safe operation. n

Frank West is the North American Industrial Machinery Manager for TÜV SÜD America, and can be reached at fwest@tuvam.com.

Notes

Approval by an NRTL for specified product categories is required under 29 CFR 1910.
The list of product types requiring NRTL approval may be located at this link.
UL508A, §1.1.
UL508A, §1.3.1.
UL508A, §1.3.2.
NFPA 79, §1.1.1.