UL 6420
Standard for Equipment Used for System Isolation and Rated as a Single Unit

Edition Number:1SCC Approved:--
Edition Date:2012-10-19DOD Approved: --
Price Code:BANSI Approved: 2018-01-08


    1 Scope and Object

    1.1 Scope

    1.1.1 General This standard applies to isolating equipment incorporating electromechanical contactors remotely controlled and monitored to provide remote isolation status indication with a defined integrity level. This equipment is intended for use as an additional isolating means on the load side of the required supply-disconnecting device and over current protection. This standard applies to isolating equipment that is to be used in circuits of which the rated voltage does not exceed 1000 Vac or 1500 Vdc. The system isolation equipment is expected to be used both as a means for removal of power for prevention of unexpected start-up of a stopped machine and as an isolator to provide protection from electric shock by ensuring the removal of electrical energy. This equipment is intended for installation in accordance with the National Electrical Code, NFPA 70 and the Electrical Standard for Industrial Machinery, NFPA 79:2012.

    Note – Reference to System Isolation Equipment is found in Article 430.109(A)(7) of the National Electrical CodeNFPA 70; in Clause 5.5.4(3), Devices for Disconnecting (Isolating) Electrical Equipment, of the Electrical Standard for Industrial Machinery, NFPA 79:2012; and in Clause 5.3.2(d) of the Standard for Safety of Machinery – Electrical Equipment of Machines – Part 1: General Requirements, IEC 60204-1. The System Isolation Equipment is not intended to fulfill the function of a motor starter or other motion control device.

    1.1.2 System isolation equipment

    1.1.2 Typical application The system isolation equipment is principally intended for industrial machine applications where, isolation of power is so frequently required that the mechanical life of a typical disconnecting means is unacceptably short or where there are multiple entry points on the machine where disconnection is required, or both.

    Note – Multiple entry points are a function of access needs and the layout of the machine.

    1.2 Object

    1.2.1 The object of this standard is to state:

    a)    The characteristics of the system isolation equipment;

    b)    The conditions of operation and behavior for the system isolation equipment, its dielectric properties, and the degree of protection provided by its enclosure where applicable;

    c)    The information to be marked on or given with the system isolation equipment;

    d)    The normal service, mounting and transport conditions of the system isolation equipment;

    e)    The construction and performance of the system isolation equipment;

    f)    The tests intended to verify that these conditions have been met, and the methods to be adopted for these tests.

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    • Cover
    • Transmittal
    • Table of Contents
      • Body
        • 1 Scope and Object
          • 1.1 Scope
          • 1.2 Object
        • 2 Normative References
        • 3 Definitions
        • 4 Classification of the System Isolation Equipment
          • 4.1 General
          • 4.2 According to the system design with single or multiple power isolation points
          • 4.3 According to the utilization category/load designation
          • 4.4 According to the required safety performance
          • 4.5 According to the normal load and overload characteristics
          • 4.6 According to the method chosen to monitor the controlled load side power circuit
          • 4.7 According to the configuration limits of the lockout station locations (See Annex , Figures and )
          • 4.8 According to the available machine control interface functions
          • 4.9 According to the reset function following restoration of power to the power circuit line terminals
        • 5 Characteristics of the System Isolation Equipment (Including the Characteristics of the Self Contained Components that are Used in the Construction of the System Isolation Equipment)
          • 5.1 General
          • 5.2 Electromechanical isolating contactor(s)
          • 5.3 Connections to internal control circuits
          • 5.4 Load side power circuit monitoring methods
          • 5.5 Lockout station
          • 5.6 Configuration requirements
        • 6 Product Information
          • 6.1 Nature of information
          • 6.2 Marking
          • 6.3 Instructions for installation, operation and maintenance
        • 7 Normal Service, Mounting and Transport Conditions
        • 8 Construction and performance requirements
          • 8.1 General
          • 8.2 Lockout switch actuator (see 8.1.4 of UL 60947-4-1A)
          • 8.3 Performance requirements (see 8.2 of UL 60947-4-1A)
          • 8.4 Electromagnetic compatibility (EMC) (see 8.3 of UL 60947-4-1A)
        • 9 Tests
          • 9.1 Kinds of test
          • 9.2 Compliance with constructional requirements
          • 9.3 Performance
          • 9.4 EMC Tests
    • Annex A
    • Annex B