Standard for Definite Purpose and Limited Duty Definite Purpose Magnetic Contactors

ARI 780/790: Standard for Definite Purpose and Limited Duty Definite Purpose Magnetic Contactors

For engineers and designers in the vital fields of HVAC and refrigeration, ensuring component reliability and performance is paramount. ARI 780/790, the "Standard for Definite Purpose and Limited Duty Definite Purpose Magnetic Contactors," provides an authoritative framework for selecting, testing, and applying these essential electrical control devices, underpinning the robust operation of countless systems.

What is ARI 780/790?

This comprehensive standard, published by the Air-Conditioning and Refrigeration Institute (ARI), establishes clear definitions, classifications, testing procedures, and performance requirements for both definite purpose and limited duty definite purpose magnetic contactors. Its primary purpose is to provide a unified, industry-accepted benchmark for manufacturers and users, ensuring consistency and reliability in these critical electrical components.

Scope & Purpose

ARI 780/790 governs contactors specifically designed for use within refrigeration and air-conditioning equipment. It delineates two primary categories: definite purpose contactors, suitable for integration within motor protection systems for compressor motors, and limited duty definite purpose contactors, intended for applications where they are not part of the primary safety or motor protection circuits. The standard does not cover general-purpose industrial contactors.

Who Must Comply?

• • Primary audience: Electrical Engineers, HVAC Design Engineers, Product Engineers, Standards Engineers, and Test Technicians involved in the design, specification, and testing of HVAC and refrigeration equipment.
• • Industries affected: HVAC Manufacturing, Refrigeration Equipment Manufacturing, and Electrical Component Manufacturing.
• • Compliance nature: Voluntary, but highly recommended for industry best practices and product quality.
• • Enforcement: Compliance is typically driven by manufacturers seeking to align their products with industry expectations and by specifiers who reference the standard in their designs.

Key Requirements Overview

The standard outlines several crucial requirements for magnetic contactors:

• • Defined Classifications: It mandates clear distinctions between "definite purpose" and "limited duty definite purpose" contactors based on their intended application and integration within safety circuits.
• • Standardized Ratings: ARI 780/790 specifies minimum data requirements for published ratings, including full-load and locked-rotor current capacities across various voltage levels, ensuring clarity for selection.
• • Rigorous Testing Protocols: Professionals must ensure contactors undergo a battery of tests, including pick-up/drop-out, coil temperature, mechanical life, and various load endurance tests under specified voltage conditions.
• • Performance Criteria: The standard defines acceptable performance parameters during these tests, ensuring the contactors can reliably establish and interrupt electrical circuits under demanding operational conditions.
• • Clear Marking and Data: Manufacturers are required to provide comprehensive marking and nameplate data, including voltage, current ratings, and any specific application limitations.

Related Standards & References

While ARI 780/790 is a foundational standard, its application is often complemented by other industry documents. For example, reference may be made to UL standards (such as UL 489 for Molded-Case Circuit Breakers, Molded-Case Switches, and Their Accessories) for specific testing methodologies and safety considerations. Additionally, ASHRAE terminology is referenced for consistent definitions within the broader HVAC&R domain