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National Electrical Safety Code® (NESC®) 2017
Section 12, Installation and Maintenance of Equipment, Paragraph 123 Protective Grounding says in part:
“Provisions must also exist for grounding during maintenance. When a conductor, bus section, or piece of equipment is disconnected for maintenance, it must be grounded. The grounding can be done with permanent grounding switches or a readily accessible means for connection portable grounding jumpers. The Part 4 Work Rules are referenced for proper procedures.”
Part 4 Work Rules, Section 445 Protective Grounds
NFPA 70E 2018
Article 100: Electrically Safe Work Condition. A state in which an electrical conductor or circuit part has been disconnected from energized parts, locked/tagged in accordance with established standards, tested to verify the absence of voltage, and, if necessary, temporarily grounded for personnel protection.
Grounded (Grounding). Connected (connecting) to ground or to a conductive body that extends the ground connection. [70:100]
120.4 Lockout/Tagout Procedures
120.4(B)(2) Stored Energy. The procedure shall include requirements for releasing stored electric or mechanical energy that might endanger personnel. All capacitors shall be discharged, and high-capacitance elements shall also be short-circuited and grounded before the associated equipment is touched or worked on. Springs shall be released or physical restraint shall be applied when necessary to immobilize mechanical equipment and pneumatic and hydraulic pressure reservoirs. Other sources of stored energy shall be blocked or otherwise relieved.
120.4(B)(7) Grounding. Grounding requirements for the circuit shall be established, including whether the temporary protective grounding equipment shall be installed for the duration of the task or is temporarily established by the procedure. Grounding needs or requirements shall be permitted to be covered in other work rules and might not be part of the lockout/tagout procedure.
120.4(B)(13) Release for Return to Service. The procedure shall identify steps to be taken when the job or task requiring lockout/tagout is completed. Before electric circuits or equipment are re-energized, tests and visual inspections shall be conducted to verify that all tools, mechanical restraints and electrical jumpers, short circuits, and temporary protective grounding equipment have been removed, so that the circuits and equipment are in a condition to be safely energized. When applicable, the employees responsible for operating the machines or process shall be notified when circuits and equipment are ready to be energized, and such employees shall provide assistance as necessary to safely energize the circuits and equipment. The procedure shall contain a statement requiring the area to be inspected to ensure that nonessential items have been removed. One such step shall ensure that all personnel are clear of exposure to dangerous conditions resulting from reenergizing the service and that blocked mechanical equipment or grounded equipment is cleared and prepared for return to service.
120.5 Process for Establishing and Verifying an Electrically Safe Work Condition
120.5(8) Where the possibility of induced voltages or stored electrical energy exists, ground the phase conductors or circuit parts before touching them. Where it could be reasonably anticipated that the conductors or circuit parts being de-energized could contact other exposed energized conductors or circuit parts, apply temporary protective grounding equipment in accordance with the following:
- Placement. Temporary protective grounding equipment shall be placed at such locations and arranged in such a manner as to prevent each employee from being exposed to a shock hazard (i.e., hazardous differences in electrical potential). The location, sizing, and application of temporary protective grounding equipment shall be identified as part of the employer’s job planning.
- Capacity. Temporary protective grounding equipment shall be capable of conducting the maximum fault current that could flow at the point of grounding for the time necessary to clear the fault.
Informational Note: ASTM F855, Standard Specification for Temporary Protective Grounds to be Used on De-energized Electric Power Lines and Equipment, is an example of a standard that contains information on capacity of temporary protective grounding equipment.
- Impedance. Temporary protective grounding equipment and connections shall have an impedance low enough to cause immediate operation of protective devices in case of unintentional energizing of the electric conductors or circuit parts.
130.8 Work Within the Limited Approach Boundary or Arc Flash Boundary of Overhead Lines
(A) Uninsulated and Energized. Where work is performed in locations containing uninsulated energized overhead lines that are not guarded or isolated, precautions shall be taken to prevent employees from contacting such lines directly with any unguarded parts of their body or indirectly through conductive materials, tools, or equipment. Where the work to be performed is such that contact with uninsulated energized overhead lines is possible, the lines shall be de-energized and visibly grounded at the point of work or suitably guarded.
(C) De-energizing or Guarding. If the lines are to be deenergized, arrangements shall be made with the person or organization that operates or controls the lines to de-energize them and visibly ground them at the point of work. If arrangements are made to use protective measures, such as guarding, isolating, or insulation, these precautions shall prevent each employee from contacting such lines directly with any part of his or her body or indirectly through conductive materials, tools, or equipment.
Temporary Protective Grounds — In-service Testing: ASTM F2249 Standard Specification for In-Service Test Methods for Temporary Grounding Jumper Assemblies Used on De-energized Electric Power Lines and Equipment
Temporary Protective Grounds — Test Specification: ASTM F855 Standard Specification for Temporary Protective Grounds to Be Used on De-energized Electric Power Lines and Equipment
130.8(F)(3) (3) Equipment Grounding. If any vehicle or mechanical equipment capable of having parts of its structure elevated near energized overhead lines is intentionally grounded, employees working on the ground near the point of grounding shall not stand at the grounding location whenever there is a possibility of overhead line contact. Additional precautions, such as the use of barricades, dielectric overshoe footwear, or insulation, shall be taken to protect employees from hazardous ground potentials (step and touch potential).
ARTICLE 250 Personal Safety and Protective Equipment
250.1 Maintenance Requirements for Personal Safety and Protective Equipment
Personal safety and protective equipment such as the following shall be maintained in a safe working condition:
(1) Grounding equipment
(2) Hot sticks
(3) Rubber gloves, sleeves, and leather protectors
(4) Test instruments
(5) Blanket and similar insulating equipment
(6) Insulating mats and similar insulating equipment
(7) Protective barriers
(8) External circuit breaker rack-out devices
(9) Portable lighting units
(10) Temporary protective grounding equipment
(11) Dielectric footwear
(12) Protective clothing
(13) Bypass jumpers
(14) Insulated and insulating hand tools
250.2 Inspection and Testing of Protective Equipment and Protective Tools
(A) Visual. Safety and protective equipment and protective tools shall be visually inspected for damage and defects before initial use and at intervals thereafter, as service conditions require, but in no case shall the interval exceed 1 year, unless specified otherwise by the applicable state, federal, or local codes and standards.
(B) Testing. The insulation of protective equipment and protective tools, such as items specified in 250.1(1) through 250.1(14), that is used as primary protection from shock hazards and requires an insulation system to ensure protection of personnel, shall be verified by the appropriate test and visual inspection to ascertain that insulating capability has been retained before initial use, and at intervals thereafter, as service conditions and applicable standards and instructions require, but in no case shall the interval exceed 3 years.
250.3 Safety Grounding Equipment
(A) Visual. Personal protective ground cable sets shall be inspected for cuts in the protective sheath and damage to the conductors. Clamps and connector strain relief devices shall be checked for tightness. These inspections shall be made at intervals thereafter as service conditions require, but in no case shall the interval exceed 1 year.
(B) Testing. Prior to being returned to service, temporary protective grounding equipment that has been repaired or modified shall be tested.
Informational Note: Guidance for inspecting and testing safety grounds is provided in ASTM F2249, Standard Specification for In-Service Test Methods for Temporary Grounding Jumper Assemblies Used on De-Energized Electric Power Lines and Equipment.
(C) Grounding and Testing Devices. Grounding and testing devices shall be stored in a clean and dry area. Grounding and testing devices shall be properly inspected and tested before each use.
Informational Note: Guidance for testing of grounding and testing devices is provided in Section 9.5 of IEEE C37.20.6, Standard for 4.76 kV to 38 kV-Rated Ground and Test Devices Used in Enclosures.
Informative Annex G Sample Lockout/Tagout Program
3.5 Where the possibility of induced voltages or stored electrical energy exists, call for grounding the phase conductors or circuit parts before touching them. Where it could be reasonably anticipated that contact with other exposed energized conductors or circuit parts is possible, call for applying ground connecting devices.
5.9 Where required, install a grounding equipment/conductor device on the phase conductors or circuit parts, to eliminate induced voltage or stored energy, before touching them. Where it has been determined that contact with other exposed energized conductors or circuit parts is possible, apply ground connecting devices rated for the available fault duty.
13.0 Lockout/Tagout Training.
Recommended training can include, but is not limited to, the following:
(1) Recognition of lockout/tagout devices
(2) Installation of lockout/tagout devices
(3) Duty of employer in writing procedures
(4) Duty of employee in executing procedures
(5) Duty of person in charge
(6) Authorized and unauthorized removal of locks/tags
(7) Enforcement of execution of lockout/tagout procedures
(8) Simple lockout/tagout
(9) Complex lockout/tagout
(10) Use of single-line and diagrammatic drawings to identify sources of energy
(11) Alerting techniques
(12) Release of stored energy
(13) Personnel accounting methods
(14) Temporary protective grounding equipment needs and requirements
(15) Safe use of test instruments
NFPA 70B 2000
3.3 General Definitions
3.3.7 Ground
3.3.7.3 Personnel Protective Ground. Bonding jumper that is intentionally installed to ground de-energized, normally ungrounded circuit conductors when personnel are working on them, to minimize voltage differences between different parts of the equipment and personnel, so as to protect against shock hazard and/or equipment damage.
3.3.7.4 Safety Ground. See 3.3.7.3, Personnel Protective Ground.
7.3 Personnel and Equipment Safety.
7.3.4 Switches or circuit breakers should be locked in an open position and tagged to provide information as to why the circuit is open and the name of the person having the key for the lock. Reference should be made to 29 CFR 1910, “Occupational Safety and Health Standards.” See Section 1910.147, “The Control of Hazardous Energy (Lockout/Tagout),” dated September 1, 1989, and Sections 1910.331 through 1910.335, “Safety Related Work Practices,” dated August 6, 1990. ANSI Z244.1, Personnel Protection — Lockout/Tagout of Energy Sources — Minimum Safety Requirements, and NFPA 70E, Standard for Electrical Safety Requirements for Employee Workplaces, are also suggested as guides in developing an effective lockout/tagout for electrical and other energy sources. Where the practice of utilizing a protective ground is employed, Section 23.3 details five major considerations for selecting the grounding equipment, including protective ground cables and clamps. All of these factors should be considered to ensure that the protective ground facilitates the operation of the protective device in the event that the circuit is accidentally energized.
8.1.7 Miscellaneous Equipment.
8.1.7.1 The availability and condition of rack-out devices, hoisting or handling apparatus, grounding equipment, hot sticks, rubber gloves, statiscopes, and other test equipment should be checked.
8.8 Gas-Insulated Substations and Gas-Insulated Equipment.
8.8.5 Maintenance and Repair of GIS and GIE.
8.8.5.1.2 Safety during maintenance and repair requires that the components on which work is to be performed are electrically isolated, de-energized, grounded, and locked/tagged out.
8.8.5.1.3 Equipment should never be depressurized until it is de-energized and grounded.
9.2 Liquid-Filled Transformers.
9.2.7.2 If a transformer is given an external visual examination, the case of the transformer should be regarded as energized until the tank ground connection is inspected and found to be adequate. If any procedure more extensive than an external visual examination is to be performed, the first precaution that should always be observed is to de-energize the transformer. De-energization should always be accompanied by approved positive lockout or lockout/tagout procedures to ensure against an unexpected re-energization and resulting hazard to personnel or equipment. De-energization should be immediately followed by a test to ensure that the equipment is de-energized. The equipment should be grounded prior to the start of any work. (See Chapter 23.)
21.3.13 Electrostatic Discharge (ESD) Grounding.
21.3.13.1.1 (Excerpt) Slowly rotating parts are normally adequately bonded or grounded through the bearings. However, parts rotating at high RPMs, such as baskets or centrifuges, should be bonded or grounded by wipers, carbon brushes, or other devices. Portable equipment can be temporarily grounded by clamping an ESD ground to the equipment.
Chapter 23 De-Energizing and Grounding of Equipment to Provide Protection for Electrical Maintenance Personnel
23.2 Steps for Providing Protection.
(4) Until they are grounded, conductors should be considered energized, and personnel should not touch them. If the test indicates there is NO VOLTAGE on the affected conductors, they should then be adequately grounded in accordance with established procedures. The conductors should be grounded to protect personnel in the event that, in spite of all precautions, the equipment does become re-energized. When capacitors are involved, they should be grounded and shorted to drain off any stored charge.
23.3 Grounding Methods and Procedures. In spite of all precautions, de-energized circuits can be inadvertently reenergized. When this occurs, adequate grounding is the only protection for personnel working on them. For this reason, it is especially important that adequate grounding procedures be established and rigidly enforced.
23.3.1 There are those who still hold to the old mistaken idea that grounding de-energized power conductors with a chain or small-diameter wire and battery clamps provides adequate safety for personnel. Such practices were not safe 50 years ago when power systems were relatively small, and they certainly are not safe on modern systems that are much larger and capable of delivering hundreds of thousands of amperes into a fault. Such currents can easily vaporize a chain or small grounding conductors without blowing fuses or opening a circuit breaker, thereby exposing personnel to dangerous voltages, vaporized conductor metal, and serious power arcs. In the interest of protecting lives, adequate grounding procedures and equipment that ensure positive personnel protection are essential.
23.3.2 A variety of terms is used to identify the grounding of de-energized electrical equipment to permit personnel to safely perform work on it without using special insulated tools. Some of these terms are safety grounding, temporary grounding, and personnel grounding. Throughout this chapter, the word grounding is used to refer to this activity; it does not refer to permanent grounding of system neutrals or non-current carrying metal parts of electrical equipment.
23.3.3 Grounding equipment consists mainly of special heavy-duty clamps that are connected to cables of adequate capacity for the system fault current. This current may well be in excess of 100,000 amperes that will flow until the circuit overcurrent protective devices operate to de-energize the conductors. The grounding equipment should not be larger than necessary, because bulkiness and weight hinder personnel while connecting them to the conductors, especially while working with hot-line sticks. When selecting grounding equipment, you should consider the following:
(1) Grounding clamps should be of proper size to fit the conductors and have adequate capacity for the fault current. An inadequate clamp can melt or be blown off under fault conditions. Hot-line clamps should not be used for grounding de-energized conductors because they are not designed to carry the high current that would flow if the circuit were to be inadvertently re-energized. They are intended to be used only for connecting tap conductors to energized overhead lines by means of hot-line sticks and are designed to carry only normal load current. If hot-line clamps are used for grounding, high fault current could melt or blow them off without operating the overcurrent protective devices to de-energize the conductors, thereby exposing personnel to lethal voltages and arc burns.
(2) Grounding cables should be of adequate capacity, which, in some instances, might require two or more to be paralleled. Three factors that contribute to adequate capacity are (1) terminal strength, which largely depends on the ferrules installed on the cable ends, (2) size to carry maximum current without melting, and (3) low resistance to keep the voltage drop across the areas in which the personnel are working at a safe level during any period of inadvertent re-energization.
(3) Solid metal-to-metal connections are essential between grounding clamps and the de-energized conductors. Conductors are often corroded and are sometimes covered with paint. Ground clamps should have serrated jaws because it is often impractical to clean the conductors. The clamps should be slightly tightened in place, given a slight rotation on the conductors to provide cleaning action by the serrated jaws, and then securely tightened. Ground clamps that attach to the steel tower, switchgear, or station ground bus are equipped with pointed or cupped set screws that should be tightened to ensure penetration through corrosion and paint, to provide adequate connections.
(4) Grounding cables should be no longer than is necessary to keep resistance as low as possible and to minimize slack in cables to prevent their violent movement under fault conditions. If the circuit should be inadvertently reenergized, the fault current and resultant magnetic forces could cause severe and dangerous movement of slack grounding cables in the area where personnel are working. Proper routing of grounding cables to avoid excessive slack is essential for personnel safety.
(5) Grounding cables should be connected between phases to the grounded structure and to the system neutral (when available) to minimize the voltage drop across the work area if inadvertent re-energization should occur. The preferred arrangement is shown in Figure 23.3.3 with the equivalent electrical diagram.
29.1.3 During maintenance or construction, de-energized, ungrounded conductors are also temporarily grounded for personnel protection against the energizing of circuit conductors. Therefore, grounding is also a temporary protective measure involving connecting the de-energized lines and equipment to earth through conductors.
29.2.45 Safety Ground. See 3.3.7.3, Personnel Protective Ground.
OSHA
1926.962 – Grounding for the protection of employees.
