Article 250 Grounding And Bonding

Question 1

Electrical systems that are grounded will limit ____ imposed by lightning, line surges, or unintentional contact with higher-voltage lines and that will ____ to earth during normal operation.

Answer 1

voltage stabilize voltage

Article 250.4 (A) (1)

Question 2

If the use of multiple grounding connections results in objectionable current and all requirements are met, one or more of the following alterations may be permitted;

Answer 2

(1) discontinue 1 or more but NOT ALL connections
(2) change locations of the connections
(3) interrupt the continuity of the conductive path

Article 250.6 (B)

Question 3

Machine screw-type fasteners and thread-forming machine screws must engage no less then ____ to properly bond a connection.

Answer 3

Two threads

Article 250.8 (A)

Question 4

The following ac systems of 50v to 1000v shall be permitted, but not required to be grounded.

Answer 4

(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 supple only adjustable-speed industrial drivers.

Article 250.21 (A)

Question 5

The following circuits shall not be grounded.

Answer 5

(1) circuits for electric cranes operating over combustible fibers in Class III locations.
(2) circuits in health care facilities as provided in 517.61 and 517.60
(3) circuits for equipment within electrolytic cell line working zones as provided in 668
(4) secondary circuits of lighting systems as provided in 411.6(A) and 680.23(A) (2)
(5) Class II load side circuits for suspended ceiling low-voltage power grid distribution systems as provided in 393.60(B)

Article 250.22

Question 6

The grounding electrode conductor connection meant for grounding service-supplied AC systems can be made at any accessible point between ____.

Answer 6

the load end of the service lateral and the service disconnecting means. This includes the bussing that the grounded service conductor is connected to.

Article 250.24 (A) (1)

Question 7

True or False

A dual-fed service may utilize a single grounding electrode conductor connection to the tie point of the grounded service conductors from each power source.

Answer 7

True

Article 250.24 (A) (3)

Question 8

True or False

The main bonding jumper may have multiple splice points between the bonded conductor and the equipment grounding conductor.

Answer 8

False

Article 250.24 (B)

Question 9

If the ungrounded service entrance conductors are installed in ____the grounded conductor shall also be installed in ____. The size of the grounded conductor in each raceway shall be based on the total circular mil area of the ungrounded conductors in the raceway, but no smaller than ____.

Answer 9

Parallel Parallel 1/O AWG

Article 250.24 (C) (2)

Question 10

A common grounding electrode conductor taped to multiple separately derived systems shall be permitted to be one of the following ____.

Answer 10

(1) not smaller than 3/O AWG
(2) a metal water pipe
(3) the metal structural frame of the building

Article 250.30 (A) (6)

Question 11

Tap connections to a common grounding electrode conductor shall be made by one of the following methods.

Answer 11

(1) connector listed as grounding and bonding equipment
(2) listed connections to busbar not smaller than 1/4” thick x 2” wide
(3) exothermic welding

Article 250.30 (A) (6)

Question 12

A metal underground water pipe must be in direct contact with the earth for ____ or more to be a permitted grounding electrode.

Answer 12

10’

Article 250.52 (A) (1)

Question 13

A metal in-ground support structure must be in direct contact with the earth vertically for ____ or more to be a permitted grounding electrode.

Answer 13

10’

Article 250.52 (A) (2)

Question 14

A concrete encased electrode shall consist of at least 20’ of either;

Answer 14

(1) one or more bare or zinc galvanized coated steel reinforcing bars or rods of not less than 1/2” diameter, installed in a continuous length or connected by steel tie wires.
(2) bare copper conductor not smaller than 4 AWG

Article 250.52 (A) (3)

Question 15

A ground ring encircling the building or structure, in direct contact with the earth, must consist of at least ___ of bare copper conductor not smaller than ____.

Answer 15

20’ 2 AWG

Article 250.52 (A) (4)

Question 16

Rod and pipe electrodes shall not be less than ____ in length and consist of either; conduit no less than ____ and have the outer surface metal coated for corrosion protection, or a rod-type electrode that is stainless steel and copper or zinc coated steel no less than ____ in diameter.

Answer 16

8’ trade size 3/4” 5/8”

Article 250.52 (A) (5)

Question 17

Plate electrodes shall expose no less than ____ of surface to the exterior soil. Bare or electrically conductive coated iron/steel plates shall be at least ____ in thickness

Answer 17

2’ 1/4”

Article 250.52 (A) (7)

Question 18

The following materials shall not be used as grounding electrodes.

Answer 18

(1) metal underground gas piping systems
(2) aluminum

Article 250.52 (B)

Question 19

If practicable, rod, pipe, and plate electrodes shall be embedded below ____.

Answer 19

permanent moisture level

Article 250.53 (A) (1)

Question 20

If a single rod, pipe, or plate electrode has a resistance to earth of ____ or less, a supplemental electrode shall not be required.

Answer 20

25 ohms

Article 250.53 (A) (2)

Question 21

If multiple supplemental electrodes are installed to meet requirements, they shall not be less than ____ apart.

Answer 21

6’

Article 250.53 (A) (3)

Question 22

The bonding jumper that is the sole connection to the supplemental rod, pipe, or plate electrode shall not be required to be larger than ____.

Answer 22

6 AWG

Article 250.53 (E)

Question 23

The ground ring shall be installed not less than ____ below the surface of the earth.

Answer 23

30”

Article 250.53 (F)

Question 24

Plate electrodes shall be installed not less than ____ below the surface of the earth.

Answer 24

30”

Article 250.53 (H)

Question 25

Rod and pipe electrodes shall be installed such that at least ____ is in contact with the soil at a depth of ____ down. Where rock bottom prevents a straight down installation, the electrode shall be driven at an oblique angle not to exceed ____.

Answer 25

8’ 8’ 45 degrees

Article 250.53 (G)

Question 26

True or False

The top end of a rod or pipe electrode shall be permitted to be aboveground as long as it and the grounding electrode are protected against physical damage.

Answer 26

True

Article 250.53 (G)

Question 27

Aluminum or copper-clad aluminum grounding electrode conductors shall not be terminated within ____ of the earth.

Answer 27

18”

Article 250.64 (A)

Question 28

True or False

Ferrous metal raceways and enclosures for grounding electrode conductors shall be bonded at each end of the raceway or enclosure

Answer 28

True

Article 250.64 (E)

Question 29

What table is used to size a grounding electrode conductor for AC systems?

Answer 29

Table 250.66

Table 250.66

Question 30

If the grounding electrode conductor connected to a single or multiple rod, pipe, plate, or any combination thereof, does not extend onto other types of electrodes that require a larger size of conductor, the grounding electrode conductor shall not be required to be larger than ____.

Answer 30

6 AWG

Article 250.66 (A)

Question 31

If the grounding electrode conductor connected to a single or multiple concrete-encased electrodes, does not extend onto other types of electrodes that require a larger size of conductor, the grounding electrode conductor shall not be required to be larger than ____.

Answer 31

4 AWG

Article 250.66 (B)

Question 32

If the grounding electrode conductor connected to a ground ring, does not extend onto other types of electrodes that require a larger size of conductor, the grounding electrode conductor shall not be required to be larger than ____.

Answer 32

the conductor used for the ground ring

Article 250.66 (C)

Question 33

Metal enclosures and raceways for service conductors and equipment shall be connected to the ____ or the ____ for systems that are not grounded.

Answer 33

grounded system conductor if the electrical system is grounded

grounding electrode conductor

Article 250.80

Question 34

True or False

For the purpose of reducing electrical noise, you may isolate an equipment enclosure from its raceway entrance when more than the circuit feeding the equipment is passing through the raceway.

Answer 34

False. There must only be the circuit feeding the equipment in the raceway.

Article 250.96 (B)

Question 35

Which raceways are required to have lockrings both inside and out to bond electrical systems over 250V.

Answer 35

Rigid Metal Conduit (RMC) and Intermediate Metal Conduit (IMC)

Article 250.97 exception (2)

Question 36

If installed on the outside, the length of the bonding jumper or conductor or equipment bonding jumper shall not exceed ____ and shall be routed with the raceway or enclosure.

Answer 36

6’

Article 250.102 (E) (2)

Question 37

True or False

In buildings of multiple occupancy, where the metallic water pipe is isolated from each individual occupancy by nonmetallic water pipe you are permitted to bond the piping system to the equipment grounding terminal of the gear supplying that occupancy. Other than service equipment.

Answer 37

True

Article 250.104 (A) (2)

Question 38

If using listed flexible metal conduit as the equipment grounding conductor, it must meet all the following conditions;

Answer 38

a. Terminated in listed fittings
b. The circuit conductors contained in the conduit are protected by overcurrent devices rated at 20A or less.
c. Trade size does not exceed 1 1/4”.
d. Total combined length does not exceed 6’
e. If used to eliminate vibration, an equipment grounding conductor shall be installed.

Article 250.118

Question 39

When housing multiple circuits in one raceway, your equipment grounding conductor is sized by ____

Answer 39

the largest overcurrent device protecting conductors in the raceway.

Article 250.122 (C)

Question 40

True or False

If the ungrounded conductors are increased in size from the minimal size required, the equipment grounding conductor must also be increased in size proportionately.

Answer 40

True

Article 250.122 (B)