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Grounding
and Bonding 60 questions 2hour CEU correspondence course based on the 2005 NEC.
250.2
A.
True
B. False
250.4(A)(2)
250.4(B)(2)
250.1
250.24(C)(2) and 310.4
250.30(A)(1)
250.30(A)(4)(b)
A. True
B. False
250.32(A) Ex
250.36
250.52(A)(3)
250.52(B)(1) and (2)
250.53(H)
250.56
250.64(B)
A.
True
B. False
250.68(A) Ex 1
A. True
B False
250.86
250.92(B)
250.102(A)
A.
True
B. False
250.102(E) Ex
250.106 FPNs
250.118(6)(b)
A. True
B. False
250.122(B)
A.
True
B. False
250.142(A)
250.142(B)
250.178
Current Flow
A. True
B. False
Reference: In parallel paths, current divides and flows through each individual parallel path in accordance with Kirchoff's current law. So, when given multiple conductive paths on which to flow, current will take all of the available paths. Yes, it’s true that more current will flow through the lower resistive path, as compared to a higher resistive path in a parallel circuit, but that’s not the question.
Current Flow
A. True
B. False
Reference: A person touching an energized metal pole, which is only grounded, will experience between 90 and 120 mA of current flow through the body, which is more than sufficient to cause electrocution*. *The destruction of life by means of electric current, IEEE/ANSI, Std 100. Remember: In parallel circuits, current divides and flows through each individual parallel path. Current Through Person I = E/R I = 90V*/1,000 ohms** I = 0.090A or 90 mA *IEEE 142, Grounding Industrial and Commercial Installations. ** IEEE 80, IEEE Guide for Safety in AC Substations. Current Through Earth I = E/R I = 120V/25 ohms I = 4.8A, not enough to trip the circuit breaker Voltage on metal parts can never be reduced or removed by grounding the metal parts to the earth. The only way to make an installation safe from a ground fault is to bond the electrical equipment to an effective ground-fault current path so that the fault current will be more than sufficient to quickly open the circuit protection device and clear the ground fault [250.2 and 250.4(A)(3)].
Current Flow
A. True
B. False
Reference: A supplementary electrode is not required to be sized in accordance with the NEC [250.54]. During a ground fault, the amount of current flowing through the grounding conductor into the earth, to the power supply, is dependent on the circuit voltage and the earth’s resistance. Assuming a circuit voltage of 120 and a ground rod resistance of 25 ohms, the current flowing through the grounding conductor into the earth, to the power supply, will be only 4.8A, not enough to trip the circuit breaker. I = E/R I = 120V/25 ohms I = 4.8A Because of the earth’s high resistance, it cannot be used as an effective ground-fault current path [250.4(A)(5)]; therefore, the grounding conductor for a supplementary electrode is not sized in accordance with the NEC [250.54].
Clear a Fault
A. True
B. False
Reference: A ground fault that relies on the earth as the fault return path to the source is not capable of carrying sufficient current to clear the ground fault [250.4(A)(5)]. Result… dangerous voltage between the metal parts and the earth exists. Assuming a circuit voltage of 120 and a ground rod resistance of 25 ohms, the current flowing through the grounding conductor into the earth, to the power supply, will be only 4.8A, not enough to trip the circuit breaker. I = E/R I = 120V/25 ohms I = 4.8A Current Through Person I = E/R I = 90V*/1,000 ohms** I = 0.090A or 90 mA *IEEE 142, Grounding Industrial and Commercial Installations. ** IEEE 80, IEEE Guide for Safety in AC Substations. If the metal pole were bonded to an effective ground-fault current path, the ground-fault current would be sufficient to quickly open the 20A circuit protection device [250.2 and 250.4(A)(3)]. Result… dangerous voltage on metal parts will be removed. I = E/ZT I = 120V/0.405 ohms* I = 296A *Effective ground-fault current path:
Service: 100 ft of 3/0 AWG Copper Service Z = 0.0766 ohms per 1,000 ft x 0.20 (Chapter 9 Table 8) Service Z = 0.015 ohms
Branch Circuit: 100 ft of 12 AWG Copper Branch Z = 1.93 ohms per 1,000 ft x 0.20 (Chapter 9 Table 8) Branch Z = 0.39 ohms
Electrical Equipment
A. True
B. False
Reference: Grounding metal parts to the earth does not reduce voltage on metal parts resulting from a ground fault because the earth cannot serve as an effective ground-fault current path [250.5(A)(5)]. Assuming a circuit voltage of 120 and a ground rod resistance of 25 ohms, the current flowing through the grounding conductor into the earth, to the power supply, will be only 4.8A, not enough to trip the circuit breaker. I = E/R I = 120V/25 ohms I = 4.8A Current Through Person I = E/R I = 90V*/1,000 ohms** I = 0.090A or 90 mA *IEEE 142, Grounding Industrial and Commercial Installations. ** IEEE 80, IEEE Guide for Safety in AC Substations. The only way to make this installation safe from a ground fault is to bond the electrical equipment to an effective ground-fault current path so that the fault current will be more than sufficient to quickly open the circuit protection device; thereby clearing the ground fault and removing dangerous touch voltage [250.2 and 250.4(A)(3)].
Electrical Equipment
A. True
B. False
Reference: Grounding metal parts to the earth does not reduce voltage on metal parts resulting from a ground fault because the earth cannot serve as an effective ground-fault current path [250.5(A)(5)]. The only way to make this installation safe from a ground fault is to bond the metal traffic signal poles and handhole covers to an effective ground-fault current path so that the fault current will be more than sufficient to quickly open the circuit protection device; thereby clearing the ground fault and removing dangerous touch voltage [250.2 and 250.4(A)(3)].
Electrical Equipment
A. True
B. False
Reference: Grounding metal parts to the earth does not reduce voltage on metal parts resulting from a ground fault because the earth cannot serve as an effective ground-fault current path [250.5(A)(5)]. The only way to make this installation safe from a ground fault is to isolate the manhole cover from energized parts or to bond the metal parts to an effective ground-fault current path so that the fault current will be more than sufficient to quickly open the circuit protection device; thereby clearing the ground fault and removing dangerous touch voltage [250.2 and 250.4(A)(3)].
Service Equipment
A. True
B. False
Reference: Grounding metal parts to the earth does not removing or reduce voltage on metal parts resulting from a ground fault because the earth cannot serve as an effective ground-fault current path [250.5(A)(5)]. The only way to make this installation safe from a ground fault is to bond service equipment to an effective ground-fault current path so that the fault current will be more than sufficient to quickly open the circuit protection device; thereby clearing the ground fault and removing dangerous touch voltage [250.2, 250.4(A)(3), and 250.24(C)].
Service Equipment
A. True
B. False
Reference: Grounding metal parts to the earth serves no part in reducing the difference of potential between metal parts and the earth from a ground fault. The only way to make this installation safe is to bond service equipment to an effective ground-fault current path so that the ground fault current will be more than sufficient to quickly open the circuit protection device; thereby clearing the ground fault and removing dangerous touch voltage [250.2, 250.4(A)(3), and 250.24(C)].
Service Equipment
A. True
B. False
Reference: The earth serves no part in stabilizing the system voltage. System voltage is stabilized by the grounding of the utility secondary winding [250.4(A)(1)].
Service Equipment
A. True
B. False
Reference: The earth serves no purpose in establishing or maintaining a zero difference of potential between metal parts of electrical equipment and the earth during a ground fault.
Separately Derived System
A. True
B. False
Reference: The earth serves no purpose in establishing or maintaining a zero difference of potential between metal parts of electrical equipment and the earth.
Separately Derived System
A. True
B. False
Reference: Grounding a separately derived system to the earth serves no purpose in removing or reducing voltage on metal parts caused by a ground fault. The only way to make this installation safe from a ground fault is to bond the metal parts of the separately derived system by using a system bonding jumper so that the ground fault current will be sufficient to quickly open the circuit protection device; thereby clearing the ground fault and removing dangerous touch voltage [250.2, 250.4(A)(3), and 250.4(A)(3)].
Separately Derived System
A. True
B. False
Reference: The NEC requires the metal case of ungrounded separately derived systems to be grounded to a grounding electrode [250.30(B)(1)].
Transformers
A. True
B. False
Reference: Grounding the metal case of a transformer to a grounding electrode is not necessary to reduce the difference of potential between the metal parts of different separately derived system. This is because there is no difference between the metal parts of the separately derived systems, because all metal parts of electrical installations are required to be bonded to an effective ground-fault current path [250.4(A)(3)]. The NEC requires the metal case of all separately derived systems to be grounded to a suitable grounding electrode [250.30(A)(3) and (7)], even though there is no technical reason for this.
Generators
A. True
B. False
Reference: Grounding metal parts to the earth does not remove or reduce voltage on metal parts resulting from a ground fault because the earth cannot serve as an effective ground-fault current path [250.5(A)(5)]. The only way to make this installation safe from a ground fault is to bond the metal case of the generator to an effective ground-fault current path so that the fault current will be more than sufficient to quickly open the circuit protection device; thereby clearing the ground fault and removing dangerous touch voltage [250.2, 250.4(A)(3), and 250.30(A)(1)].
Remote Building
A. True
B. False
Reference: Grounding metal parts to the earth does not remove or reduce voltage on metal parts resulting from a ground fault because the earth cannot serve as an effective ground-fault current path [250.5(A)(5)]. The only way to make this installation safe from a ground fault is to bond the building disconnecting means to an effective ground-fault current path so that the fault current will be more than sufficient to quickly open the circuit protection device; thereby clearing the ground fault and removing dangerous touch voltage [250.2, 250.4(A)(3), and 250.32(B)].
Remote Building
A. True
B. False
Reference: Grounding of the remote building disconnecting means to the earth is necessary to reduce voltage on the metal parts from lightning; thereby reducing the likelihood of a fire caused by elevated voltage seeking a path to the earth by arcing across combustible materials. The equipment grounding conductor provides the low-impedance path to the source necessary to clear a ground fault; its function is not to serve as a path for lightning to the earth.
Outdoor Metal Light Pole
A. True
B. False
Reference: Grounding metal parts to the earth does not remove or reduce voltage on metal parts resulting from a ground fault because the earth cannot serve as an effective ground-fault current path [250.5(A)(5)]. The only way to make this installation safe from a ground fault is to bond the metal light pole to an effective ground-fault current path so that the fault current will be more than sufficient to quickly open the circuit protection device; thereby clearing the ground fault and removing dangerous touch voltage [250.2 and 250.4(A)(3)].
Outdoor Metal Light Pole
A. True
B. False
Reference: If lightning strikes the pole, the luminaire on the pole is toast. Nothing can be done about this.
Outdoor Metal Light Pole
A. True
B. False
Reference: Grounding a metal light pole to the earth does nothing to prevent damage to interior wiring and equipment of a building from lightning. Interior wiring and equipment can be protected from lightning-induced voltage transients on the circuit conductors by the use of properly designed TVSS protection devices.
Outdoor Metal Light Pole
A. True
B. False
Reference: Ralph Lee, in a 1966 study, proved that lightning does not crack the concrete of a concrete encased grounding electrode.
Sensitive Electronic Equipment
A. True
B. False
Reference: If lightning strikes the pole, the The earth serves no purpose in improving power quality.
Sensitive Electronic Equipment
A. True
B. False
Reference: Grounding sensitive electrical equipment to the same electrode serves no purpose in preventing or reducing ground-loop currents. This is because ground-loop currents flow when improper neutral-to-ground connections are made on the load side of service equipment or separately derived systems in violation of 250.142. To remove ground-loop currents, simply ensure the installation is in compliance with the NEC.
Sensitive Electronic Equipment
A. True
B. False
Reference: Grounding sensitive electronic equipment to the earth serves no purpose in improving equipment performance or power quality. As a matter of fact, grounding equipment to an isolated grounding electrode can cause equipment damage when lightning current flows produces a potential difference between the counter-poise ground and the structure ground.
Sensitive Electronic Equipment
A. True
B. False
Reference: There will always be voltage between the neutral and ground terminals at a receptacle. For example: the NEC recommends that under a load conduction, a maximum voltage drop of 3% for the feeder, which works out to be 3.6V for a 120V circuit. Under this condition, the voltage (feeder neutral voltage drop) as measured between the receptacles’ neutral and ground terminals would be 1.8V if no current flows through the branch circuit supplying the receptacle. Naturally if the branch circuit is loaded, the voltage between the neutral and ground terminal would be greater than 1.8V. A study by the Electrical Power Research Institute (EPRI) demonstrated that elevated neutral-to-ground voltage has no affect on equipment performance.
Stray Voltage or Neutral-to-Earth
Voltage (
A. True
B. False
Reference: Grounding metal parts to the earth serves no purpose
in reducing stray or
Stray Voltage or
A. True
B. False
Reference: Bonding metal parts to an equipotential plane does
reduce the difference of potential between the metal parts and the
equipotential plane, but stray or
TVSS
A. True
B. False
Reference: The earth serves no purpose in the operation of a TVSS device. TVSS protection devices protect electrical equipment by shunting high-frequency impulse currents away from the load and back to the source via the circuit conductors, not via the earth.
General
A. True
B. False
Reference: Because the voltage gradient in salt water is much lower than fresh water, the likelihood of death will be greater in a fresh water marina.
General
A. True
B. False
Reference: If the water is contained in a nonmetallic sink or bathtub, where there is no conductive path to the power supply, the GFCI protection device will not tip and the water will be energized with a dangerous voltage gradient!
General
A. True
B. False
Reference: The lightning protection system is required to be bonded to the building or structure grounding electrode system by both NFPA 780, Lightning Protection Code and NFPA 70, the National Electrical Code [250.106].
58. A ground-fault current path is an electrically conductive path from the point of a line-to-case fault extending to the ______
A. ground
B. earth
C. electrical supply source
D. none of the above
250.2
59. Electrical systems are grounded to the ______ to stabilize the system voltage.
A. ground
B. earth
C. electrical supply source
D. none of the above
250.4(A)(1)
60. For grounded systems, the metal parts of the electrical equipment in a building or structure must be connected to the _____ for the purpose of limiting the voltage to ground on these materials.
A. ground
B. earth
C. electrical supply source
D. none of the above
250.4(A)(1)
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