Article 250 Test
Is a corner-grounded delta transformer connection required to be grounded?
No, it's not required but permitted.
Is a grounding electrode at a separate building supplied by a common service required if only one circuit supplies the building?
No.
What is the grounding electrode conductor used for?
A conductor used to connect the system grounded conductor or equipment to a grounding electrode or to a point on the grounding electrode system. Grounding electrode- a conducting object through which a direct connection to the earth is established.
What must be done to non-conductive coating on equipment to be grounded?
Non-conductive coatings (such as paint, lacquer, and enamel) on equipment to be grounded shall be removed from threads and other contact surfaces to ensure good electrical continuity or be connected by means of fittings designed so as to make such removal unnecessary.
List specific fastened in place or permanently connected equipment that must be grounded regardless of voltage.
Switchgear and Switchboard frames and structures Pipe Organs Motor frames Enclosures for Motor Controllers Elevators and Cranes Garages, Theaters, and Motion Picture Studios Electric Signs Motion Picture Projection Equipment Remote-Control, Signaling, and Fire Alarm Circuits. Luminaires Skid-Mounted Equipment. Motor-Operated Water Pumps Metal Well Casings
List example of nonelectrical equipment equipment that must be grounded.
The metal parts of the following nonelectrical equipment shall be connected to the equipment grounding conductor: (1) Frames and tracks of electrically operated cranes and hoists. (2) Frames of non-electrically driven elevator cars to which electrical conductors are attached (3) Hand-operated metal shifting ropes or cables of electric elevators.
List the five types of available AC systems and the conductor that shall be grounded.
(1) Single-phase, 2-wire, one conductor (2) Single-phase, 3-wire, the neutral conductor (3) Multiphase systems having one wire common to all phases - the neutral conductor. (4) Multiphase systems where one phase is grounded, one phase conductor. (5) Multiphase systems in which one phase is used in (2) - the neutral conductor
What is the purpose of the main bonding jumper?
For a grounded system, an unspliced main bonding jumper shall be used to connect the equipment grounding conductor(s) and the service-disconnect enclosure to the grounded conductor within the enclosure for each service disconnect in accordance with 250.28
Is the Earth to be used as the sole equipment grounding conductor or fault current path?
No.
How is a screw used for the main bonding jumper identified?
With a green finish.
List the circuits that shall not be grounded.
(1.) Circuits for electric cranes operating over combustible fibers in Class III locations, as provided in 503.155 (2.) Circuits in health care facilities as provided in 517.61 and 517.160 (3.) Circuits for equipment within electrolytic cell working zone as in 411.6(A) (4.) Secondary circuits of lighting systems as provided in 680.23(A)(2) (5.) Secondary circuits of lighting systems as provided in 680.23(A)(2).
5 Parameters in Connecting the Grounding electrode conductor of a service supplied by an AC system. (1.)
(1.) General - The Grounding electrode conductor connection shall be made at any accessible point from the load end of the overhead service conductors, service drop, underground service conductors, or lateral to, including the terminal or bus to which the grounded service conductor is connected at the service disconnecting Means.
5 Parameters in Connecting the Grounding electrode conductor of a service supplied by an AC system. (2.)
(2.) Outdoor Transformer. Where the transformer supplying the service is located outside the building, at least one additional grounding connection shall be made from the grounded service conductor to a grounding electrode, either at the transformer or elsewhere outside the building. Except on high-impedance grounded neutral systems.
5 Parameters in Connecting the Grounding electrode conductor of a service supplied by an AC system. (3.)
(3.) Dual-Fed Services - For services that are dual fed (double ended) in a common enclosure or grouped together in separate enclosures and employing a secondary tie, a single grounding electrode conductor connection to the tie point of the grounded conductor(s) from each power source shall be permitted.
List two ways the grounding electrode and grounding equipment of a separate building supplied by a common service may be connected.
By a grounding rod and equipment grounding conductor.
List cord and plug connected equipment in residential occupancies required to be grounded.
a.) refrigerators, freezers, and air conditioners. b.) Clothes-washing, clothes-drying, dish-washing machines, ranges, kitchen waste disposers, information technology equipment, sump pumps and electrical aquarium equipment c.) Hand-held motor-operated tools, stationary and fixed motor-operated tools, and light industrial motor operated tools d.) Motor-operated appliances of the following types: hedge clippers, lawn mowers, snow blowers, and wet scrubbers e.) Portable handlamps
5 Parameters in Connecting the Grounding electrode conductor of a service supplied by an AC system. [condensed answer]
(1) General - Grounding Electrode Conductor shall be made accessible. (2) Outdoor Transformers - Needs an additional grounding connection) (3) Dual-Fed Services- Single Grounding Electrode Conductor at tie point. (4) Main Bonding Jumper as Wire or Busbar - The Grounding Electrode Conductor shall be permitted to be connected to the equipment grounding terminal, bar, or bus to which the main bonding jumper is connected to the equipment grounding terminal bar or bus in the service equipment. (5) Load-Side Grounding Connections - A Grounding Conductor Shall NOT be connected to normally non-current carrying metal parts of equipment, the Equipment Grounding Conductor, OR reconnected to Ground on load side of service disconnect.
What are the six specific requirements covered in article 250?
(1) Systems, circuits, and equipment required, permitted, or not permitted to be grounded. (2) Circuit conductors to be grounded on grounded systems. (3) Location of grounding connections. (4) Types and sized of grounding and bonding conductors and electrodes. (5) Methods of grounding and bonding. (6) Conditions under which guards, isolation, or insulation may be substituted for grounding.
List the conditions where an alternating circuit of 50 to 1000 volts must be grounded.
(1) Where the system can be grounded so that the maximum voltage to ground on the ungrounded conductors does not exceed 150 volts. (2) Where the system is 3-phase, 4-wire, wye connected in which the neutral conductor is used as a circuit conductor. (3) Where the system is a 3-phase, 4-wire, delta connected in which the midpoint of one phase winding is used as a circuit conductor.
When do fastened in place or permanently connected equipment need to be grounded?
(1) Where within 8 ft vertically or 5 ft horizontally of ground or grounded metal objects and subject to contact by persons. (2) Where located in a wet or damp location and not isolated (3) Where in electrical contact with metal (4) Where in a hazardous (classified) location as covered by articles 500 through 517 (5) Where supplied by a wiring method that provides an equipment grounding conductor, except as permitted by 250.86 exception No. 2 for short sections of metal enclosures. (6) Where equipment operates with any terminal at over 150 volts to ground.
5 Parameters in Connecting the Grounding electrode conductor of a service supplied by an AC system. (4.)
(4.) Main Bonding Jumper as Wire or Bus bar - Where the main bonding jumper specified in 250.28 is a wire or bus bar and is installed from the grounded conductor terminal bar or bus to the equipment grounding terminal bar or bus in the service equipment, the grounding electrode conductor shall be permitted to be connected to the equipment grounding terminal, bar, or bus to which the main bonding jumper is connected.
5 Parameters in Connecting the Grounding electrode conductor of a service supplied by an AC system. (5.)
(5.) Load-Side Grounding Connections - A grounded conductor shall not be connected to normally non-current carrying metal parts of equipment, to equipment grounding conductor(s), or be reconnected to ground on the load side of the service disconnecting means except as otherwise permitted in this article.
What type of material(s) and device(s) are permitted for the main bonding jumper?
Copper or other corrosion resistant material. Devices shall be a wire, bus, screw, or similar suitable conductor.
List the types of equipment grounding conductors (exclude conditions)
(1) A copper, aluminum, or copper-clad aluminum conductor. (2) Rigid metal conduit. (3) Intermediate metal conduit. (4) Electrical metallic tubing. (5) Listed flexible metal conduit (6) Listed liquidtight flexible metal conduit flexible metal conduit and flexible metallic tubing and Iiquidtight flexible metal conduit in the same ground-fault current path does not exceed (6 ft). (7) Flexible metallic tubing where the tubing is terminated in listed fittings. (8) Armor of Type AC cable as provided in 320.10S. (9) The copper sheath of mineral-insulated, metal-sheathed cable Type MI. (10) Type MC cable that provides an effective ground-fault current path (11) Cable trays as permitted in 392.10 and 392.60. (12) Cablebus framework as permitted in 370.60(1). (13) Other listed electrically continuous metal raceways and listed auxiliary gutters. (14) Surface metal raceways listed for grounding.
List the AC systems of 50 to 1000 volts that shall be permitted to be grounded.
(1) Electrical systems used exclusively to supply industrial electric furnaces for melting, refining, tempering, and the like (2) Separately derived systems used exclusively for rectifiers that supply only adjustable-speed industrial drives. (3) Separately derived systems supplied by transformers that have a primary voltage rating of 1000 volts or less, provided that all the following conditions are met: a) The system is used exclusively for control circuits. b) The conditions of maintenance and supervision ensure that only qualified persons service the installation. c) Continuity of control power is required. (4) Other systems that are not required to be grounded in accordance with the requirements of 250.20(B)
List the conditions where an alternating circuit of less than 50 volts must be grounded.
(1.) Where supplied by transformers, if the transformer supply system exceeds 150 Volts to ground. (2.) Where supplied by transformers, if the transformers supply system is ungrounded. (3.) Where installed outside as a overhead conductors.
How may an insulated or covered conductor larger than # 4 AWG be identified.
250.119 (A)(1) As an equipment grounding conductor at each end and at every point where accessible. (A)(2) Identification shall encircle the conductor and shall be accomplished by one of the following: a.) Stripping the insulation or covering from the entire exposed length. b.) Coloring the insulation or covering green at the termination. c.) Marking the insulation or covering with green tape or green adhesive labels at the termination.
How shall the identification of equipment grounding conductors in a flexible cord be identified.
An uninsulated equipment grounding conductor shall be permitted, but, if individually covered, the covering shall have a continuous outer finish that is either green or green with one or more yellow stripes.
What is the general requirement for the performance of fault current paths?
Electrical equipment, wiring, and other electrically conductive material likely to become energized shall be installed in a manner that creates a low-impedance circuit from any point on the wiring system to the electrical supply source to facilitate the operation of overcurrent devices should a second ground fault from a different phase occur on the wiring system. The Earth shall not be considered an effective fault-current path.
What is the general requirement for bonding of electrically conductive materials and other equipment?
Normally Non-conductive materials that are likely to become energized shall be connected together and to the electrical supply source in a manner that establishes an effective ground-fault current path.
What is the general requirement for grounding of electrical equipment?
Normally non-current carrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected to the earth so as to limit the voltage lines and limit the voltage to ground on those materials.
How shall the equipment grounding conductor be identified?
Shall be permitted to be bare, covered, or insulated. Individually covered or insulated equipment grounding conductors shall have a continuous outer finish that is either green or green with one or more yellow stripes.
Generally, what does article 250 cover?
The general requirements for grounding and bonding of electrical installations and specific requirements.
What is the general requirement for grounding electrical systems?
They shall be connected to the earth in a manner that will limit the voltage imposed by lightning, line surges, or unintentional contact with higher voltage lines that will stabilize the voltage to earth during normal operation.
List the exception to grounding cord and plug connected equipment in other than residential occupancies.
Tools and portable handlamps likely to be listed in wet or conductive locations shall not be required to be connected to an equipment grounding conductor where supplied through an isolating transformer with an ungrounded secondary of not over 50 volts.
Does double insulation nullify the grounding requirement in hazardous locations?
Yes, it shall NOT be required where protected by double insulation.
List additional cord and plug connected equipment requiring grounding in other than residential occupancies.
a.) Refrigerators, freezers, and air conditioners. b.) Clothes-washing, clothes-drying, dish-washing machines; information technology equipment; sump pumps and electrical aquarium equipment. c.) Hand-held motor operated tools, stationary and fixed motor-operated tools, and light industrial motor-operated tools. d.) Motor-operated appliances of the following types: hedge clippers, lawn mowers, snow blowers, and wet scrubbers. e.) Portable handlamps f.) Cord-and-plug-connected appliances used in damp or wet locations or by persons standing on the wet ground or on metal floors or working inside of metal tanks or boilers. g.) Tools likely to be used in wet or conductive locations.
List the methods acceptable for connection of grounding conductors and bonding jumpers.
(1) Listed pressure connectors (2) Terminal bars (3) Pressure connectors listed as grounding and bonding equipment. (4) Exothermic welding process (5) Machine screw-type fasteners that engage not less than two threads in the enclosure (6) Thread-forming machine screws that engage not less than two threads in the enclosure. (7) Connections that are part of a listed assembly (8) Other listed means.