B11 LMSS Module 5

NFPA 79 Key Definitions

• Shall: Indicates mandatory requirements.
• Should: Suggests recommendations or advice, not required.
• Listed: Equipment or services evaluated by an authoritative organization, meeting designated standards.
• Direct Opening Operation: Achieved by the movement of a switch actuator through non-resilient members, without relying on springs.
• Hazardous Condition: A scenario where a person may face immediate or long-term harm.
• Safety Circuit: Part of a control system performing safety-related functions to maintain safety.
• Controlled Stop: Machine halts while retaining power to the actuators.
• Uncontrolled Stop: Machine halts by cutting power, initiating brakes or other mechanical stops.

NFPA 79 Control Functions

• Control Functions in Failure Scenarios:
  • Protective devices are essential (interlocks, guards, trip devices).
  • Electrical circuits must include protective interlocking.
  • Proven circuit techniques and components should be utilized.
  • Partial or complete redundancy may be required.
  • Functional testing should be provisioned.

NFPA 79 Operator Interface & Control Devices

• Controls must be rigidly mounted in clean, dry areas to minimize damage.
• Hand controls must be positioned at least 0.6 meters above the servicing level.
• Operator positions must avoid hazardous situations and minimize inadvertent operations.
• Start pushbuttons should be above or to the left of stop buttons.
• Emergency stops must be accessible and operable at each control station.

NFPA 79 Control Equipment: Location, Mounting & Enclosures

• Equipment should be easily accessible for maintenance and operation.
• Protective constructions must align with UL standards (e.g., UL 508, UL 508A, NEMA 250).
• Minimum enclosure protection is Type 1.
• Working spaces in front of control cabinets must be at least 762 mm (30 in).

Wiring Practices

• All wire connections need securing against accidental loosening.
• Proper identification is required for connections based on the conductor's type and area.
• Shields on conductors should prevent fraying and allow easy disconnection.
• Tags must be permanent and legible.
• Terminal blocks must be configured to prevent crossover wiring.

Conductors & Cable Requirements

• Conductors must be insulated and made of copper.
• Insulation should be flame retardant.
• Conductors are color-coded for identification (e.g., green for ground, black for ungrounded).

OSH Act and OSHA Overview

• Passed in 1970 to protect workers from workplace hazards.
• OSHA enforces and sets safety standards under the US Department of Labor.
• General Duty Clause requires employers to maintain a hazard-free workplace.

Responsibilities Under OSHA

• Suppliers: Ensure machines are designed for effective hazard control.
• Users: Ought to establish protective programs against hazardous energy.
• Personnel: Must follow the hazardous energy control programs.

Case Studies

• Secretary v Loren Cook: Highlighted compliance issues regarding machine guarding; defense of infeasibility established.
• Secretary v Walmart: Focused on workplace accidents and penalties for safety violations.

Risk Management Terminology

• Risk Reduction: Actions taken to minimize potential hazards.
• Acceptable Risk: Level of risk deemed manageable and justifiable.
• Lockout/Tagout: Procedures to prevent the accidental energization of machinery, crucial for safety in handling hazardous energy.

Learning Objectives

• Cover essential topics including conductors, wiring practices, electric motors, and safety regulations in relation to NFPA 79 standards.

Test your knowledge of the key definitions and mandatory requirements outlined in NFPA 79. This quiz covers applications, compliance with existing machinery, and important regulatory clauses. Perfect for those studying electrical standards and safety guidelines.