Conformity Magazine- May 2008 - (Page 30) • 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 30 Conformity mAy 2008 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. Frank West is the North American Industrial Machinery Manager for TÜV SÜD America, and can be reached at fwest@tuvam.com. Notes 1. 2. 3. 4. 5. 6. 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 www.conformity.com/1742. UL508A, §1.1. UL508A, §1.3.1. UL508A, §1.3.2. NFPA 79, §1.1.1. FAST Link www.conformity.com/1740 http://www.conformity.com/1742 http://www.conformity.com/1740
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