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Insulation and grounding are two recognized means of preventing injury during electrical equipment operation. Placing non-conductive material such as plastic around the conductor may provide conductor insulation. Grounding may be achieved through the use of direct connection to a known ground such as a metal cold water pipe.
The metal housing or enclosure around a motor or the metal box in which electrical switches, circuit breakers and controls are placed protect the equipment from dirt and moisture and prevent accidental contact with exposed wiring.
There is, however, a hazard associated with housings and enclosures. A malfunction within the equipment, such as deteriorated insulation, may create an electrical shock hazard. Many metal enclosures are connected to a ground to eliminate the hazard, but if a “hot” wire contacts a grounded enclosure, a ground fault results which normally will trip a circuit breaker or blow a fuse.
Metal enclosures and containers are usually grounded by connecting them with a wire going to ground. This wire is called an equipment-grounding conductor. Most portable electric tools and appliances are grounded by this means. There is one disadvantage to grounding. A break in the grounding system may occur without the user’s knowledge.
Insulation may be damaged by hard usage on the job or simply by aging. If this damage causes the conductors to become exposed, the hazards of shocks, burns, and fire will exist. Double insulation may be used as additional protection on the live parts of a tool, but double insulation does not provide protection against defective cords and plugs or against heavy moisture conditions. The use of a ground fault circuit interrupter (GFCI) is one method used to overcome grounding and insulation deficiencies.
The ground fault circuit interrupter is a fast-acting circuit breaker which senses small imbalances in the circuit caused by current leakage to ground and, in a fraction of a second, shuts off the electricity. The GFCI continually matches the amount of current going to an electrical device against the amount of current returning from the device along the electrical path. Whenever the amount “going” differs from the amount “returning” by approximately 5 milliamps, the GFCI interrupts the electric power within as little as one fortieth of a second.
The GFCI will not protect a person from line to line contact hazards, such as a person holding two “hot” wires, or a hot and a neutral wire in each hand. It does provide protection against the most common form of electrical shock hazard, the ground fault. It also provides against fires, overheating and destruction of insulation on wiring.
Scope
The provisions of 1910.331 through 1910.335 cover electrical safety-related work practices for both qualified persons (those who have training in avoiding the electrical hazards of working on or near exposed energized parts) and unqualified persons (those with little or no such training) working on, near, or with the following installations:
- Premises wiring. Installations of electric conductors and equipment within or on buildings or other structures, and on other premises such as yards, carnival, parking, and other lots, and industrial substations:
- Wiring for connection to supply. Installations of conductors that connect to the supply of electricity, and
- Other wiring. Installations of other outside conductors on the premises.
- Optical fiber cable. Installations of optical fiber cable where such installations are made along with electric conductors. NOTE: See 1910.399 for the definition of “qualified person.” See 1910.332 for training requirements that apply to qualified and unqualified persons.
Regulatory citations
- 29 CFR 1010 Subpart S — Electrical
Key definitions
- Competent person. One who is capable of identifying existing and predictable hazards in the surroundings or working conditions that are unsanitary, hazardous, or dangerous to employees and who has authorization to take prompt corrective measures to eliminate them.
- Ground. A conducting connection, whether intentional or accidental, between an electric circuit or equipment and the earth, or to some conducting body that serves in place of the earth.
- Grounded. Connected to the earth or to some conducting body that serves in place of the earth.
- Grounded, effectively. Intentionally connected to earth through a ground connection or connections of sufficiently low impedance and having sufficient current-carrying capacity to prevent the buildup of voltages that may result in undue hazards to connected equipment or to persons.
- Grounded conductor. A system or circuit conductor that is intentionally grounded.
- Grounding conductor. A conductor used to connect equipment or the grounded circuit of a wiring system to a grounding electrode or electrodes.
- Grounding conductor, equipment. The conductor used to connect the noncurrent-carrying metal parts of equipment, raceways, and other enclosures to the system grounded conductor, the grounding electrode conductor, or both, at the service equipment or at the source of a separately derived system.
- Grounding electrode conductor. The conductor used to connect the grounding electrode to the equipment grounding conductor, to the grounded conductor, or to both, of the circuits at the service equipment or at the source of a separately derived system.
- Ground-fault circuit-interrupter (GFCI). A device intended for the protection of personnel that functions to deenergize a circuit or a portion of a circuit within an established period of time when a current to ground exceeds some predetermined value that is less than that required to operate the overcurrent protective device of the supply circuit.
- Qualified person. One who has received training in and has demonstrated skills and knowledge in the construction and operation of electric equipment and installations and the hazards involved.
Note 1 to the definition of “qualified person”: Whether an employee is considered to be a “qualified person” will depend upon various circumstances in the workplace. For example, it is possible and, in fact, likely for an individual to be considered “qualified” with regard to certain equipment in the workplace, but “unqualified” as to other equipment. (See 1910.332(b)(3) for training requirements that specifically apply to qualified persons.)
Note 2 to the definition of “qualified person”: An employee who is undergoing on-the-job training and who, in the course of such training, has demonstrated an ability to perform duties safely at his or her level of training and who is under the direct supervision of a qualified person is considered to be a qualified person for the performance of those duties.
Summary of requirements
Grounding requirements are covered in 1910.304(g)(1) through (g)(9):
- Systems to be grounded (1910.304(g)(1))
- Conductor to be grounded (1910.304(g)(2))
- Portable and vehicle-mounted generators (1910.304(g)(3))
- Grounding connections (1910.304(g)(4))
- Grounding path (1910.304(g)(5))
- Supports, enclosures, and equipment to be grounded (1910.304(g)(6))
- Non-electrical equipment (1910.304(g)(7))
- Methods of grounding fixed equipment (1910.304(g)(8))
- Grounding of systems and circuits of 1000 volts and over (high voltage) (1910.304(g)(9))