Understanding NEC Article 670: Industrial Machinery
NEC Article 670 outlines the electrical requirements for industrial machinery, addressing supply conductor sizing, overcurrent protection, disconnecting means, and nameplate data. These guidelines ensure the safe and reliable operation of machinery in industrial environments while integrating with facility electrical systems.
Scope of Article 670
This article applies to:
- Electrical systems for industrial machinery, including power and control equipment.
- Equipment that may be purchased and assembled on-site or shipped preassembled for reassembly at its location.
Referenced Standards:
- NFPA 79: Electrical Standard for Industrial Machinery.
- NFPA 70E: Standard for Electrical Safety in the Workplace.
Key Requirements for Industrial Machinery
- Machine Nameplate Data (670.3)
- Industrial machines must have a permanent nameplate including:
- Supply voltage, number of phases, frequency, and full-load current.
- Maximum ampere rating for short-circuit and ground-fault protection.
- Short-circuit current rating (SCCR) based on approved methods or UL 508A standards.
- Electrical diagram or drawing references.
- Full-load current must account for all operational equipment simultaneously under normal conditions.
- Industrial machines must have a permanent nameplate including:
- Supply Conductors and Overcurrent Protection (670.4)
- Conductor Ampacity: Must be at least 125% of the full-load current for the highest-rated motor plus the sum of all other motors and resistance heating loads.
- Overcurrent Protection: Protective devices must not exceed the combined ratings of branch-circuit protective devices and the calculated full-load current.
- Disconnecting means must isolate the machine and may omit overcurrent protection when the machine provides it internally.
- Short-Circuit Current Ratings (670.5)
- Machines must not be installed where the available fault current exceeds the SCCR.
- Field marking is required, displaying available fault current and the date of the calculation.
- Overvoltage Protection (670.6)
- Machinery with safety circuits must include overvoltage protection to safeguard against surge damage, which could compromise safety interlocks or cause equipment failure.
Special Considerations
- Duty Cycle and Load Factors
- Load calculations must consider duty cycles, as intermittent loads may affect conductor sizing.
- Reduced or oversized conductors are permitted when justified by specific operating characteristics.
- Disconnecting Means Accessibility
- Disconnects must comply with NFPA 79 for accessibility, placement, and locking provisions.
- Field Integration
- Machinery assembled on-site must conform to Article 670 and applicable NEC articles. Preassembled units follow NFPA 79 standards.
Applications
Article 670 supports safe installations in:
- Manufacturing Facilities: Production machinery and assembly lines.
- Industrial Automation: Robotics and CNC machines.
- Material Processing: High-current industrial applications.
Conclusion
NEC Article 670 provides comprehensive requirements for the safe installation, operation, and maintenance of industrial machinery. By addressing nameplate data, conductor sizing, overcurrent protection, and SCCR compliance, the article ensures safety and functionality in industrial environments.
