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The purpose of this document is to give outline details regarding American legislation and the selection of interlocks for your machinery.

IEEE and American National Standards Institute (ANSI) Standards:

  • ANSI Z244.1 (2003) Control of Hazardous Energy-Lockout/Tagout and Alternative Methods (For more info see below)
  • IEEE Std C37.20.1-1993 for Metal-Enclosed Low-Voltage Power Circuit Breaker Switchgear.
  • IEEE Std C37.20.2-1993 for Metal-Clad and Station-Type Cubicle Switchgear.
  • ANSI/IEEE Std C37.20.3-1987 for Metal-Enclosed Interrupter Switchgear.
  • IEEE Std C37.20.6-1997 for 4.76kV to 38kV Rated Grounding and Testing Devices Used In Enclosures.
  • IEEE Std C37.35-1995 Guide for the Application, Installation, Operation, and Maintenance of High-Voltage Air Disconnecting and Interrupter Switches.
  • ANSI/IEEE Std C37.38-1989 for Gas-Insulated, Metal-Enclosed Disconnecting, Interrupter, and Grounding Switches.
  • IEEE Std C37.59-1996 Standard Requirements for Conversion of Power Switchgear Equipment.
  • ANSI Std C37.121-1989 Requirements for Unit Substations.
  • IEEE Std 241-1990 Recommended Practice for Electric Power Systems in Commercial Buildings.
  • IEEE Std 499-1997 Recommended Practice for Cement Plant Electric Drives and Related Electrical Equipment.
  • ANSI/IEEE Std 502-1985 Guide for Protection, Interlocking, and Control of Fossil-Fueled Unit-Connected Steam Stations.
  • IEEE Std 510-1983 Recommended Practices for Safety in High-Voltage and High-Power Testing.
  • IEEE Std 1015-1997 Recommended Practice for Applying Low-Voltage Circuit Breakers Used in Industrial and Commercial Power Systems.

National Electric Code (NEC) Articles and National Fire Protection Association (NFPA) Standards:

  • NEC Article 440-33 Air-Conditioning and Refrigeration Equipment.
  • NEC Article 440-34 Air-Conditioning and Refrigeration Equipment.
  • NEC Article 460-24 Switching.
  • NEC Article 490-21 Circuit Interrupting Devices, High-Voltage Fuses.
  • NEC Article 490-22 Equipment Over 600 Volts, Isolating Means.
  • NEC Article 490-42 Interlocks - Interrupter Switches.
  • NEC Article 490-45 Interlocks - Circuit Breakers.
  • NEC Article 665-22 Guarding, Grounding, and Labeling.
  • NEC Article 710-22 Isolating Means.
  • NEC Article 710-24 Metal-Enclosed Power Switchgear and Industrial Control Assemblies.
  • NEC Article 810-71 Interior Installation - Transmitting Stations.
  • NFPA-70E Standard for Electrical Safety Requirements for Employee Workplaces 2000 Edition.
  • NFPA-79 Electrical Standard for Industrial Machinery 1997 Edition.

Occupational Safety and Health Administration (OSHA) Regulations:

  • 1910.212 - Machine Guarding: General Requirements.
  • 1910.217 - Mechanical power presses.
  • 1910.255 - Resistance welding.
  • 1910.261 - Pulp, paper, and paperboard mills.
  • 1910.262 - Textiles.
  • 1910.265 - Sawmills.
  • 1910.269 - Electric Power Generation, Transmission, and Distribution.
  • 1910.305 - Wiring methods, components, and equipment for general use.
  • 1910.308 - Special systems.
  • 1910.333 - Selection and use of work practices.
  • 1910.66 - Powered platforms for building maintenance.
  • 1926.405 - Wiring methods, components, and equipment for general use.
  • 1926.406 - Specific purpose equipment and installations.
  • 1926.408 - Special systems.

ANSI Z244.1 (2003) Control of Hazardous Energy-Lockout/Tagout and Alternative Methods

Cited in OSHA interpretations and private sector materials, the Z244.1 Standard is a significant standard used by many, if not most, SH&E professionals as a resource for addressing control of hazardous energy and lockout/tagout. The scope and purpose of the standard is to establish requirements for the control of hazardous energy associated with machines, equipment, or processes that could cause injury to personnel. The purpose of this standard is to establish requirements and performance objectives for procedures, techniques, designs and methods that protect personnel where injury can occur as a result of the unexpected release of hazardous energy. Unexpected release of hazardous energy can include any unintended motion, energization, start-up or release of stored energy, deliberate or otherwise, from the perspective of the person(s) at risk.

Here are the basics:

  • The unexpected release of hazardous energy continues to be a major occupational safety issue. Despite the efforts of many stakeholders involved with this issue, deaths and injuries continue at unacceptably high levels.
  • All forms of stored, potentially hazardous, energy must be considered. Technological advangements have required that additional methods be developed to control hazardous energy.
  • The purpose of the standard is to protect personnel from injury and death that may result from the unexpected release of hazardous energy.
  • Lockout/tagout is the primary method of hazardous energy control.
  • Based upon risk assessment, some alternative methods of control are permitted, including Trapped Key Interlocks.

The following information describes the main areas in for which Castell Interlocks are particularly suitable. Please do not hesitate to contact us if you would like to discuss the interlocking of your machinery. We would be pleased to offer a free site visit, literature and details of an interlocking scheme to suit your safety requirements.

Safety of Machinery - Trapped Key Interlocking

Castell Trapped key Interlocks are used to achieve the required safety on numerous types of machinery in a complete range of industries. They are particularly suitable for :-

  1. both Power Interlocking and all types of Control Circuit interlocking
  2. machinery with different types of power source. e.g. pneumatic, hydraulic
  3. machinery with fixed or variable run-down times
  4. harsh environments. Castell have a range of material specifications and weatherproofing
  5. areas requiring full-body access. If the guard swings shut during access the interlocked electrical circuit is not re-made as wiring is not required to the guards
  6. full-body access within the guarded area but out of sight from the gate / control panel. In such areas persons could be accidentally trapped inside the danger area and the machinery re-started. Castell Personnel Keys can be released upon access to prevent this from happening
  7. robot compounds where access must be restricted to the end of a cycle and where safe "teaching" is required from inside the guarded area
  8. interlocking of mechanical devices needed to ensure safe access. e.g. "scotch pins"
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