NEMA WD-AG 1-2017 Application Guide for Isolated Ground Wiring Devices.pdf

1、NEMA Standards PublicationNational Electrical Manufacturers AssociationNEMA WD-AG 1-2017Application Guide for Isolated Ground Wiring DevicesNEMA Standards Publication WD-AG 1-2017 Application Guide for Isolated Ground Wiring Devices Published by: National Electrical Manufacturers Association 1300 No

2、rth 17thStreet, Suite 900 Rosslyn, Virginia 22209 www.nema.org 2017 National Electrical Manufacturers Association. All rights including translation into other languages, reserved under the Universal Copyright Convention, the Berne Convention for the Protection of Literary and Artistic Works, and the

3、 International and Pan American Copyright Conventions. 2017 National Electrical Manufacturers Association NOTICE AND DISCLAIMER The information in this publication was considered technically sound by the consensus of persons engaged in the development and approval of the document at the time it was

4、developed. Consensus does not necessarily mean that there is unanimous agreement among every person participating in the development of this document. The National Electrical Manufacturers Association (NEMA) standards and guideline publications, of which the document contained herein is one, are dev

5、eloped through a voluntary consensus standards development process. This process brings together volunteers and/or seeks out the views of persons who have an interest in the topic covered by this publication. While NEMA administers the process and establishes rules to promote fairness in the develop

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7、y, or other damages of any nature whatsoever, whether special, indirect, consequential, or compensatory, directly or indirectly resulting from the publication, use of, application, or reliance on this document. NEMA disclaims and makes no guaranty or warranty, expressed or implied, as to the accurac

8、y or completeness of any information published herein, and disclaims and makes no warranty that the information in this document will fulfill any of your particular purposes or needs. NEMA does not undertake to guarantee the performance of any individual manufacturer or sellers products or services

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10、s document should rely on his or her own independent judgment or, as appropriate, seek the advice of a competent professional in determining the exercise of reasonable care in any given circumstances. Information and other standards on the topic covered by this publication may be available from othe

11、r sources, which the user may wish to consult for additional views or information not covered by this publication. NEMA has no power, nor does it undertake to police or enforce compliance with the contents of this document. NEMA does not certify, test, or inspect products, designs, or installations

12、for safety or health purposes. Any certification or other statement of compliance with any health or safetyrelated information in this document shall not be attributable to NEMA and is solely the responsibility of the certifier or maker of the statement. NEMA WD-AG 1-2017 Page i 2017 National Electr

13、ical Manufacturers Association CONTENTS Foreword ii Scope ii Section 1 Application Considerations 1.1 Why? 1 1.2 Where? 1 1.3 When? . 1 1.4 How? 2 Section 2 Characteristics of Isolated Ground Wiring Devices 3 Section 3 Marking and Identification 3.1 UL Requirements . 4 3.2 Federal Specification Requ

14、irements . 5 3.3 Types . 5 3.4 Accessories . 5 Section 4 National Electrical Code Requirements 4.1 General 7 4.2 Basic Grounding and Bonding Requirements . 7 4.3 Isolated Ground Devices . 7 Section 5 Wiring Methods 5.1 Metallic Raceway System 9 5.2 Non-Metallic Raceway System 10 5.3 Flexible Metalli

15、c Conduit, Armored Cable and Metal Clad Cable Systems 11 5.4 Non-metallic Cable Systems . 11 5.5 Retrofit . 12 5.6 Separately Derived Systems . 12 5.7 Hospitals 12 Section 6 Maintenance, Replacement, Systems Extensions, Troubleshooting 6.1 Maintenance and Replacement . 13 6.2 System Extensions 14 6.

16、3 Troubleshooting . 14 NEMA WD-AG 1-2017 Page ii 2017 National Electrical Manufacturers Association Foreword This Application Guide for Isolated Ground Wiring Devices was developed by the Wiring Device Section of the National Electrical Manufacturers Association. In the preparation of this applicati

17、on guide, input of users and other interested parties and organizations has been sought and evaluated. Inquiries, comments, and proposed changes are welcome and should be submitted to: Senior Director, Technical Operations National Electrical Manufacturers Association 1300 North 17thStreet, Suite 90

18、0 Rosslyn, VA 22209 The purpose of this application guide is to assist the user in proper installation and use of isolated ground devices. This guide was developed by the NEMA Wiring Device Section. Section approval of the standard does not necessarily imply that all section members voted for its ap

19、proval or participated in its development. At the time it was approved, the group was composed of the following members: BJB Electric LP, Ringgold, GA Eaton, Peachtree City, GA Enerlites Inc., Irvine, CA Hubbell Canada LP, Pickering, ON Hubbell Inc., Shelton, CT Interpower Corporation, Oskaloosa, IA

20、 Legrand / Pass To minimize voltage potential between grounded conductive surfaces to reduce shock hazard; To provide a suitable path to earth for lightning.These basic objectives are met through the specific application of a general philosophy requiring: Connecting the grounded circuit conductor (n

21、eutral) and the equipment grounding conductor onlyat the service entrance equipment; Connecting the exposed metal parts of equipment to the equipment grounding system; Bonding interior metal piping systems at the service entrance.4.3 Isolated Ground DevicesThe NEC sections dealing with isolated grou

22、nd devices are “exceptions“ to the general rules concerning the grounding system. They do not alter either the objectives or philosophy of the NEC. Rather, specific provision is made for their installation consistent with the basic requirements. The principle NEC provisions in Article 250 allows for

23、 isolated ground devices where such a device is needed to reduce electrical noise. It must be run with the circuit conductors to an equipment grounding conductor terminal at any point between the branch circuit source and the service or applicable separately derived system. Basic requirements for sa

24、fety must still be maintained, including Grounding of exposed metal parts, boxes and wiring systems Metal faceplates must be grounded.Since the mounting system of isolated ground receptacles is isolated from the equipment ground wire Article 406 contains additional provisions regarding wall plates a

25、nd non-metallic boxes. NEMA WD-AG 1-2017 Page 8 2017 National Electrical Manufacturers Association Isolated ground receptacles installed in nonmetallic boxes shall be covered with a nonmetallic faceplate. An exception is permitted to allow a metal faceplate if the box contains a feature or accessory

26、 that permits the effective grounding of the faceplate. In metallic boxes the mounting system and wall plate are grounded through the normal means including the use of self or auto-grounding clips. Special precautions must be taken for application in patient care areas of health care facilities as i

27、ndicated in Section 517. NEMA WD-AG 1-2017 Page 9 2017 National Electrical Manufacturers Association Section 5 Wiring Methods 5.1 Metallic Raceway System Since a metallic raceway system serves as an equipment grounding conductor, an additional grounding conductor is normally optional. For an isolate

28、d ground system, an additional insulated/isolated ground conductor is required. In a metallic raceway system that uses a supplemental equipment grounding conductor and an isolated ground conductor, the grounding conductors should be readily distinguishable from each other, such as a green insulated

29、conductor for supplemental grounding and a green with yellow striping insulated conductor for the isolated ground. Metal outlet boxes are used in metallic conduit system branch circuits. If a supplemental equipment grounding conductor is used, it must be bonded to each box. The isolated ground condu

30、ctor must be connected to the grounding terminal of the isolated ground receptacle. This connection should be made by means of an insulated “pigtail“ so that grounding continuity is maintained when receptacles are changed or removed, in accordance with NEC Article 250. The isolated-ground conductor

31、should not be connected to the outlet box since the isolation would be defeated. Care should be taken to ensure that any uninsulated grounding conductor in the box does not make contact with the isolated ground terminal. NEMA WD-AG 1-2017 Page 10 2017 National Electrical Manufacturers Association 5.

32、2 Non-Metallic Raceway System Non-metallic systems with non-metallic boxes by nature are not grounded. Nonmetallic systems are required to have an equipment grounding conductor to ground all metallic parts of equipment supplied by the circuit and grounding terminals of receptacles on the circuits. M

33、etal wall plates should not be used with isolated ground receptacles mounted in nonmetallic boxes unless there is a feature or accessory that effectively grounds the faceplate. If isolated ground receptacles are the only receptacles on the circuit, only an insulated/isolated ground conductor is nece

34、ssary. If other receptacles or equipment are on the same circuit with the isolated ground receptacle, then an additional equipment grounding conductor is necessary. The isolated equipment grounding conductor is insulated to prevent contact with grounded metal objects other than the intended groundin

35、g terminal. Care may be required to maintain this insulation at a sub-panel in accordance with NEC Article 250. If metal boxes, covers, wall plates or equipment are used in conjunction with nonmetallic raceway, an equipment grounding conductor is necessary to ground metal boxes and all exposed metal

36、 parts of the system, For isolated ground receptacles, a separate insulated grounding conductor must be run in the conduit system. The grounding conductors must be connected in the same way as described in “Metallic Raceway Systems“ and, to preserve isolation of the grounding circuit, must not be in

37、terconnected. NEMA WD-AG 1-2017 Page 11 2017 National Electrical Manufacturers Association 5.3 Flexible Metallic Conduit, Armored Cable and Metal Clad Cable Systems These wiring methods follow the same rules as “Metallic Raceway Systems.“ The maximum permitted length of a flexible metallic conduit w

38、ithout an equipment grounding wire is six feet. When flexible metallic conduit is used in an isolated ground system, an additional insulated grounding conductor must be installed and identified as the isolated ground conductor. Armored Cable (AC) and Metal Clad Cable (MC) have built-in equipment gro

39、unding means which bond to the outlet box via an appropriate box connector. When these cables are used as an isolated ground system, an insulated conductor within the cable must be used as the isolated ground conductor. Reidentification, when required, is accomplished according to NEC Article 250. 5

40、.4 Non-Metallic Cable Systems Isolated ground can only be obtained in systems using non-metallic cable if the cable has an insulated grounding conductor. Note: Metal wall plates should not be used with isolated ground receptacles mounted in nonmetallic boxes unless there is a feature or accessory th

41、at effectively grounds the faceplate. NEMA WD-AG 1-2017 Page 12 2017 National Electrical Manufacturers Association 5.5 Retrofit Metal outlet boxes must be grounded. A separate insulated isolated ground conductor must be installed in a manner suitable for the wiring method used. NEVER use an isolated

42、 ground receptacle to replace a conventional receptacle in a conventionally grounded (non-IG) system in an ungrounded system. 5.6 Separately Derived Systems There are no requirements in NEC Article 250 in conflict with isolated ground principles. The isolated ground conductor must terminate on the l

43、oad side of the separately derived system rather than being carried back to the service. 5.7 Hospitals It should be noted that isolated ground circuits have no relationship to isolated power systems as described in NEC Article 517. NEMA WD-AG 1-2017 Page 13 2017 National Electrical Manufacturers Ass

44、ociation Section 6 Maintenance, Replacement, Systems Extensions, Troubleshooting 6.1 Maintenance and Replacement As with all electrical wiring devices, effective maintenance for isolated ground receptacles begins with careful selection and proper initial installation. Guidance for choosing the most

45、suitable unit for a specific installation can usually be found in literature available from manufacturers of isolated ground devices. It is vital for the safe performance of the device in its intended manner that it is installed completely according to the instructions of the manufacturer, including

46、 circuit rating and polarity of the circuit conductors. At any time when it is determined that an isolated ground device is misapplied, improperly installed, or damaged, it must be replaced or the improper condition corrected. When not functioning properly, an isolated ground receptacle may present

47、hazards to personnel or to the electronic equipment it is thought to be protecting from ground circuit noise. Periodically each isolated ground receptacle should be checked electrically for ground continuity and visually examined for signs of damage. In addition, as for all receptacles, thorough mai

48、ntenance requires ongoing verification that the device contacts firmly grip an inserted plug; the installation remains complete, with proper cover or plate, and securely fastened to the outlet box; and that the device is not warm to the touch due to loose connections or excessive loading on the bran

49、ch circuit. For assurance that the entire isolated ground system is safe and suitable for use, routine maintenance procedures should be applied as well to the power supply cords and extension cords that are connected to isolated ground receptacles. Cords, plugs, and connectors should be free of damage. Strain relief clamps of plugs and connectors must grip cord jackets tightly and across the full width and depth of the clamp. Plugs and connectors must be used only with devices of compatible configuration. It is never proper to modify