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Plate electrodes shall be exposed not less than ______ inches below the surface of the earth. 250.53(7)
2 sq ft (0.186 sq m)
how much ohms must rod, pipes, and plate electrodes have?
25 ohms or less
what is the minimum length of a ground rod?
8 feet
pipe or conduit electrodes shall be not less than?
8' in length
2" (50mm) of concrete
A concrete-encased electrode used for service grounding must be covered with a minimum of?
Grounding electrode
A conducting object through which a direct connection to earth is established.
Grounding conductor
A conductor used to connect equipment or the grounded circuit of a wiring system to a grounding electrode or electrodes.
Grounding electrode conductor (GEC)
A conductor used to connect the system grounded conductor or the equipment to a grounding electrode or to a point on the grounding electrode system.
Grounding clip
A listed spring clip used to secure a bonding conductor to an outlet box.
Ground rod
A metal rod or pipe used as a grounding electrode.
Separately derived system
A premises wiring system whose power is derived from a source of electric energy or equipment other than a service. Such systems have no direct electrical connection, including a solidly connected ground circuit conductor, to supply conductors originating in another system.
5A
A single-phase system has two legs, Leg A and Leg B. If Leg A is carrying 35A and Leg B is carrying 30A,the current carried by the neutral is?
Grounded conductor
A system or circuit conductor that is intentionally grounded.
aluminum
All of the following are suitable materials for ground rods, except______.
Supplemental electrode
An additional electrode (commonly a driven rod or pipe) required where the primary electrode is an underground metal water pipe in direct contact with the earth.
Effective ground fault path
An intentionally constructed, permanent, low-impedance electrically conductive path designed and intended to carry current under ground-fault conditions from the point of a ground fault on a wiring system to the electrical supply source and that facilitates the operation of the overcurrent protective device or ground-fault detectors on a high-impedance grounded system.
Short circuit
An often unintended low-resistance path through which current flows around, rather than through, a component or circuit.
4/0 service conductors
Assuming the use of 75 Celsius copper conductors, a 230A commercial service would require
Ungrounded conductors
Conductors in an electrical system that are not intentionally grounded
Bonding
Connected to establish electrical continuity and conductivity
Grounded
Connected to ground or to a conductive body that extends the ground connection.
Grounding connections
Connections used to establish a ground; they consist of a grounding conductor, a grounding electrode, and the earth surrounding the electrode.
what determines the size of the over current device
EGC electrical ground conductor
4AWG copper
If you are bonding multiple disconnects and the size of the service-enterance conductor is 3/0, the size of the bonding jumper is ______.
System grounding
Intentional connection of one of the circuit conductors of an electrical system to ground potential.
The grounding conductor or neutral in a grounded system services two main purposes, give one purpose
It provides low-impedance return path for the flow of fault current to the source to facilitate the operation of the over current devices in the circuit
Ungrounded conductor
Item B in figure RQ01 represents the?
grounded conductor
Item C in figure RQ01 represents the ?
main bonding jumper
Item F in figure RQ01 represents the?
Auxiliary electrodes
Metallic electrodes pushed or driven into the earth to provide electrical contact for the purpose of performing measurements on grounding electrodes or ground grid systems.
NEC article 250, Part III
Methods for grounding an electric service
neutral bus in the main panelboard
Residential electrical service are grounded by connecting the grounded conductor to grounding electrode at the?
14 AWG copper
The EGC for a flexible metal conduit connection to a motor supplied with a 15A circuit is_____.
short circuit
The conducting connection, whether intentional or accidental,between any of the conductors of an electrical system is known as a?
Equipment grounding conductor (EGC)
The conductive path(s) that provide a ground-fault current path and connect normally noncurrent-carrying metal parts of equipment together and to the system grounded conductor, or to the grounding electrode conductor, or both.
Neutral conductor
The conductor connected to the neutral point of a system that is intended to carry current under normal conditions.
Main bonding jumper
The connection between the grounded circuit conductor and the equipment grounding conductor at the service.
Equipment bonding jumper
The connection between two or more portions of the equipment grounding conductor
Ground
The earth or a conducting connection to the earth.
2 AWG copper
The main bonding jumper for 4/0 service conductors is _____.
5' (1.5m)
The maximum distance allowed by the NEC to connect a grounding conductor to a water pipe after the pipe enters the building is _______.
3' (1 m)
Touch voltage extends to a distance of approximately_______.
NEC Section 250.53(A)(1)
Upper end of rod must be below permanent moisture level
bonding jumper
When a metal water pipe is used as a grounding electrode, what must be provided around the water meter?
grounding is required in which of the following situations
Where supplied by transformer exceeds 150V to ground
neutral
Which conductor(s) are grounded on a single-phase, three-wire,120/240Vsystem?
No. 4
Which of the following copper AWG sizes should be used for the grounding conductor for a 200A service using 3/0 copper conductors?
An underground gas line
Which of the following is an NEC violation when used as a grounding electrode?
a grounding clip
Which of the following is used to connect a ground rod with a grounding conductor?
Supplemental grounding electrodes must meet the following requirements
Withstand and dissipate repeated surge currents, Provide corrosion resistance to various soil chemistries, Be rugged enough to drive into the soil with minimal effort and damage
What is a short circuit?
a conducting connection, whether intentional or accidental, between any of the conductors of an electrical system, whether it is from line-to-line or line-to-ground
what is a short circuit?
a conducting connection, whether intentional or accidental, between any of the conductors of an electrical system, whether it is from line-to-line or line-to-ground
What does an effective ground-fault path provide?
a permanent, continuous path to safely conduct fault current, and has low enough impedance to limit the voltage to ground and facilitate the operation of circuit protective devices
A separate derived system is?
a premises wiring system whose power is derived from the source of electrical energy other than a service
In a three-point test to measure the resistances of a grounding electrode with most ground testers
an auxiliary current electrode and an auxiliary potential electrode are required
What is a ground fault
an unintentional, electrically conducting connection between an ungrounded conductor of an electrical circuit and the normally noncurrent-carrying conductors, metal enclosures, metallic raceways, metallic equipment, or the earth
what is a ground fault?
an unintentional, electrically conducting connection between an ungrounded conductor of an electrical circuit and the normally noncurrent-carrying conductors, metal enclosures, metallic raceways, metallic equipment, or the earth
where can the system bonding jumper be installed?
at the generator or any point in between
The maximum value of fault current depends on the?
available capacity the system can deliver to the point of fault
The continuity between service equipment and enclosures is maintained by
bonding
NEC Article 250
covers the requirements for grounding
A complete resistance curve should be plotted for
each season of the year
How can you determine if a generator is a separately derived system,
examine the transfer switch
AC systems over 1,000 volts must be?
grounded if supplying mobile/portable equipment
Certain systems operating at less than 50 volts require?
grounding
what makes ground to earth connections
grounding electrodes, ground grids, and ground mats
An equipment bonding jumper may be installed either....
inside or outside of a raceway or enclosure
Wire-type grounding electrode conductors may be spliced at any location by means of?
irreversible compression fittings or exothermic welding
Flexible metal conduit can be used as an equipment ground if....
it meets the NEC® installation requirements
Liquidtight flexible metal conduit can also be used as an equipment ground if....
it meets the NEC® installation requirements
grounded electrode conductor
item E in figure RQ01 represents the?
why are circuits grounded?
limit the voltage to ground on the circuit and ensure the stability and continuity of the electrical system
An earth ground resistance tester is used to?
measure soil resistivity and the resistance of the installed grounding electrode system
If a non metallic box is used with a type NM cable
no connection to the box is required
Equipment grounding conductors connect the
noncurrent-carrying metal parts of equipment, conduit, boxes, or enclosures to the system grounded conductor, the grounding electrode conductor, or both
What does a grounding system do?
protects life and equipment against electrical faults
Exothermic welding may only be performed by?
qualified individuals
Ground testers may only be used by
qualified personnel
Other types of electrodes include?
rod and pipe, plate electrodes, and other local metal underground systems such as water piping
If the neutral is not needed for voltage requirements, it still must be?
run to the service and connect to the grounded electrode conductor and equipment grounding conductor at the service
A grounding clip or other device is used to?
secure the equipment grounding conductor to each receptacle to ensure continuity of the grounding system
If the neutral and all phase conductors in the generator are switched, the transformer is?
separately derived
A poorly grounded system can result in?
serious injury or death due to hazardous step and touch voltages
There are two categories of grounding. what are they?
system grounding and equipment grounding
NEC 250, part x discusses the grounding requirements for?
systems over 1kV
Subsequent measurements need only be made at?
the 62% point and 10 feet (3 meters) on each side
A common grounding electrode conductor is required to ground both?
the circuit grounded conductor and the equipment grounding conductor
The equipment grounding conductor (EGC) is....
the conductor used to interconnect and bond the noncurrent-carrying metal parts of equipment, raceways, and other enclosures to the system grounded conductor and/or the grounding electrode conductor at the service equipment or the source of a separately derived system
When installing grounding at more than one building what must be done with the GCC and EGC?
the grounding circuit conductor and equipment grounding conductor must both be extended to the second building
Equipment bonding jumpers has to be sized for?
the overcurrent device
System grounding relates to
the service-entrance equipment and its bonded components
The main bonding jumper must be rated for
the size of the service conductors
The size of the grounding electrode conductors depends on?
the size of the service entrance
If the neutral and all phase conductors are switched
the system is separately derived
If the neutral and all phase conductors are switched what is the transformer?
the transformer is separately derived
The grounded conductor or neutral permits
utilization of power at line-to-neutral voltage and provides a low-impedance return path for the flow of fault current
The fall-of-potential method measures the?
voltage drop between the grounding electrode and an auxiliary potential electrode
Incorrect readings may be obtained
where there are natural soil currents caused by electrolytic action, or induced currents in the soil, instrument, or electrical leads
