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Grounding and Bonding 60 questions 2hour CEU correspondence course based on the 2005 NEC.

  1. A (n) _____ is an unintentional, electrically conducting connection between an ungrounded conductor of an electrical circuit and the normally non–current-carrying conductors, metallic enclosures, metallic raceways, metallic equipment, or earth.
  1. grounded conductor
  2. ground fault
  3. equipment ground
  4. bonding jumper

250.2

  1. For grounded systems, noncurrent-carrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected to earth so as to limit the voltage-to-ground on these materials.

               A.  True
               B.  False

250.4(A)(2)

  1. For ungrounded systems, non–current-carrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected together and to the supply system grounded equipment in a manner that creates a permanent, low-impedance path for ground-fault current that is capable of carrying _____.
  1. the maximum branch circuit current
  2. at least twice the maximum ground fault current
  3. the maximum fault current likely to be imposed on it
  4. the equivalent to the main service rating

250.4(B)(2)

  1. Grounding electrode conductor fittings shall be protected from physical damage by being enclosed in _____ where there may be a possibility of physical damage.
  1. metal
  2. wood
  3. the equivalent of a or b
  4. none of these

250.1

  1. Where the service-entrance phase conductors are installed in parallel, the size of the grounded conductor in each raceway shall be based on the size of the ungrounded service-entrance conductor in the raceway, but not smaller than _____.
  1. 1/0 AWG
  2. 2/0 AWG
  3. 3/0 AWG
  4. 4/0 AWG

250.24(C)(2) and 310.4

  1. An unspliced _____ that is sized based on the derived phase conductors shall be used to connect the equipment grounding conductors of a separately derived system to the grounded conductor.
  1. system bonding jumper
  2. equipment grounding conductor
  3. grounded conductor
  4. grounding electrode conductor

250.30(A)(1)

  1. Each tap conductor to a common grounding electrode conductor for multiple separately derived systems shall be sized in accordance with _____ based on the derived phase conductors of the separately derived system it serves.
  1. 250.122
  2. 250.66
  3. 310.15
  4. 250.118

250.30(A)(4)(b)

  1. A grounding electrode at a separate building or structure is required where one multiwire branch circuit serves the building or structure.

A.  True
B.  False

250.32(A) Ex

  1. High-impedance grounded neutral systems shall be permitted for three-phase ac systems of 480 volts to 1000 volts where the conditions of maintenance and supervision ensure that only qualified persons service the installation and _____.
  1. continuity of power is required
  2. ground detectors are installed on the system
  3. line-to-neutral loads are not served
  4. all of these

250.36

  1. An electrode encased by at least 2 in. of concrete, located within and near the bottom of a concrete foundation or footing that is in direct contact with the earth, is allowed as a grounding electrode when it consists of _____.
  1. at least 20 ft of ˝ in. or larger steel reinforcing bars or rods
  2. at least 20 ft of bare copper conductor of 4 AWG or larger
  3. a or b
  4. none of these

250.52(A)(3)

  1. _____ shall not be used as grounding electrodes.
  1. Metal underground gas piping systems
  2. Aluminum electrodes
  3. Metal well casings
  4. a and b

250.52(B)(1) and (2)

  1. Plate electrodes shall be installed not less than _____ below the surface of the earth.
  1. 8 ft
  2. 24 in.
  3. 30 in.
  4. 18 in.

250.53(H)

  1. When multiple ground rods are used for a grounding electrode, they shall be separated not less than _____ apart.
  1. 6 ft
  2. 8 ft
  3. 20 ft
  4. 12 ft

250.56

  1. Grounding electrode conductors _____ and larger that are not subject to physical damage can be run exposed along the surface, if securely fastened to the construction.
  1. 6 AWG
  2. 8 AWG
  3. 10 AWG
  4. 4 AWG

250.64(B)

  1. The connection of the grounding electrode conductor to a buried grounding electrode (driven ground rod) shall be made with a listed terminal device that is accessible.

A.  True

B.  False

250.68(A) Ex 1

  1. Metal enclosures and raceways for other than service conductors shall be grounded except as permitted by 250.112(I).

A. True

B  False

250.86

  1. Bonding jumpers shall be used around _____ knockouts that are punched or otherwise formed so as to impair the electrical connection to ground. Standard locknuts or bushings shall not be the sole means for this bonding.
  1. concentric
  2. eccentric
  3. field-punched
  4. a or b

250.92(B)

  1. Equipment bonding jumpers shall be of copper or other corrosion-resistant material. A bonding jumper shall be a _____ or similar suitable conductor.
  1. conductor
  2. bus
  3. screw
  4. any of these

250.102(A)

  1. The general rule for equipment bonding jumpers installed on the outside of a raceway or enclosure is that they are not permitted to be longer than 6 ft, but an equipment bonding jumper can be longer than 6 ft at outside pole locations for the purpose of bonding or grounding isolated sections of metal raceways or elbows installed in exposed risers of metal conduit or other metal raceways.

A.  True

B.  False

250.102(E) Ex

  1. Metal raceways, enclosures, frames, and other noncurrent-carrying metal parts of electric equipment installed on a building equipped with a lightning protection system may require spacing from the lightning protection conductors, typically 6 ft through air or ___ through dense materials, such as concrete, brick, wood, etc.
  1. 2 ft
  2. 3 ft
  3. 4 ft
  4. 6 ft

250.106 FPNs

  1. Liquidtight flexible metal conduit (LFMC) up to trade size ˝ can be used as the equipment grounding conductor if the length in any ground return path does not exceed 6 ft and the circuit conductors contained in the conduit are protected by overcurrent devices rated at _____ or less when the conduit is not installed for flexibility after installation.
  1. 15A
  2. 20A
  3. 30A
  4. 60A

250.118(6)(b)

  1. When ungrounded conductors are increased in size, the equipment grounding conductor is not required to be increased because it is not a current-carrying conductor.

A. True

B.  False

250.122(B)

  1. The grounded circuit conductor is permitted to ground noncurrent-carrying metal parts of equipment, raceways, and other enclosures at the supply side or within the enclosure of the ac service disconnecting means.

A.  True

B.  False

250.142(A)

  1. A grounded circuit conductor shall not be used for grounding noncurrent-carrying metal parts of equipment on the load side of _____.
  1. the service disconnecting means
  2. the separately derived system disconnecting means
  3. overcurrent protection devices for separately derived systems not having a main disconnecting means
  4. all of these

250.142(B)

  1. The grounding conductor for secondary circuits of instrument transformers and for instrument cases shall not be smaller than _____ AWG copper.
  1. 18
  2. 16
  3. 14
  4. 12

250.178

Current Flow

  1. When electrical current is given multiple conductive paths on which to flow, current will only take the path of least resistance.

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

  1. It is important to ground metal parts to a suitable grounding electrode, so that in the event of a ground fault, dangerous ground-fault current will be shunted into the earth, away from persons; thereby protecting them against electric shock.

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

  1. The grounding conductor for a supplementary grounding electrode (for example, a ground rod for a machine tool) must have the capacity to conduct safely any fault current likely to be imposed on it. This is accomplished by sizing the conductor in accordance with Table 250.66 or Table 250.122, depending on the conditions.

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

  1. Electrical equipment must be grounded so that sufficient fault current will flow through the circuit protection device to quickly open and clear the ground fault. For example, a 20A circuit breaker will trip and de-energize a 120V ground fault to a metal pole that is grounded to a 25 ohm ground rod.

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

  1. Electrical equipment must be grounded to ensure that dangerous voltage on metal parts resulting from a ground fault can be reduced to a safe value.

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

  1. Metal traffic signal poles and handhole covers must be grounded to a suitable grounding electrode to ensure that dangerous voltage on metal parts resulting from a ground fault can be reduced to a safe value.

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

  1. Grounding of metal manhole covers to a suitable grounding electrode ensures that dangerous voltage on metal parts resulting from a ground fault can be reduced to a safe value.

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

  1. Service equipment must be grounded to a grounding electrode to ensure that dangerous voltage on metal parts, caused by a ground fault, can be removed or be reduced to a safe value.

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

  1. Service equipment is grounded to a grounding electrode to ensure that metal parts, subject to a ground fault, remain at the same potential as the earth.

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

  1. Grounding of service equipment to a grounding electrode is necessary to stabilize the system voltage.

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

  1. The grounding of service equipment ensures that all metal parts of equipment that personnel can come into contact with, are always at or near zero (0) volts with respect to ground (earth).

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

  1. The metal parts of separately derived systems are grounded to ensure that the voltage, as measured between the metal parts of the electrical installation and the earth remains at the same potential during a ground fault.

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