Lesson 4: Grounding Electrodes and the Grounding Electrode System

The ? provides the essential function of connecting the electrical system, equipment, or both to the earth.

grounding electrode

Which part of Article 250 provides the requirements for grounding electrodes and the grounding electrode system?

Part III

The purpose of a grounding electrode is to function as the connection between the ground (earth) and grounded electrical systems and electrical equipment.

True

Foundations and footings that are not in direct contact with the earth qualify as grounding electrodes.

False

Section 250.50 requires all grounding electrodes that are present at each building or structure served to be bonded together to form the grounding electrode system.

True

The resistance between a grounding electrode (such as a ground rod) and earth can vary depending on which of the following?

-Ambient temperature

-Geographical location

-Mineral content of the soil

A metal underground water pipe that is in direct contact with the earth for ? or more is a Code-recognized grounding electrode and must be included in the grounding electrode system.

10'

Which of the following is not permitted as a grounding electrode?

Underground metal gas piping

The NEC makes it clear that if any grounding electrodes are present at a building or structure served by electrical power, the electrodes must be bonded together to form a grounding electrode system.

True

The NEC requires that a metal underground water pipe electrode be buried not less than 30 inches below grade level.

False

The NEC generally prohibits the use of an interior metal water piping system to connect grounding electrodes to the grounding electrode conductor beyond a distance of ? from the point of entrance to the building or structure.

5'

A concrete-encased electrode can be installed in either a vertical or horizontal orientation, and it must have not less than ? of one or more conductive rebar or rods, or a 4 AWG bare copper conductor.

20'

Where two services are installed on the same building or structure as permitted in 230.2(A), they are required to be connected to the same grounding electrode system.

True

A ground ring electrode must completely encircle a building or structure, be not less than 20 feet in length, and be buried not less than ? below the grade.

30"

Which of the following persons was responsible for the research and development that eventually resulted in the NEC requirements for a concrete-encased electrode?

Herbert G. Ufer

Plate electrodes must be buried not less than 24 inches below grade.

False

Stainless steel rod electrodes generally must not be less than ? in diameter.

5/8"

A plate electrode is required to have not less than ? of surface in direct contact with the earth.

2 ft2

A single grounding electrode of the rod, pipe, or plate type must generally be supplemented by an additional electrode of any type specified in Section 250.52(A)(2) through (8).

True

A single grounding electrode of the rod, pipe, or plate type is not required to be supplemented by an additional electrode of any type specified in Section 250.52(A)(2) through (8) if the single electrode has a resistance to Earth of ? or less.

25 Ω

The supplemental grounding electrode for a metal water pipe electrode is permitted to be bonded to the grounding electrode conductor, the grounded service-entrance conductor, the nonflexible grounded service raceway, or any grounded service enclosure.

True

A rod or pipe electrode is generally required to be driven to a depth of not less than ? .

8'

A rod or pipe electrode that cannot be driven into the earth because of encountering rock bottom is permitted to be buried at a depth of not less than ? .

30"

A distance of not less than ? shall be maintained between an eight-foot ground rod and the next closest ground rod.

6'

Where an auxiliary grounding electrode is installed for equipment such as parking lot light poles, the connection of the auxiliary electrode is in addition to the required ? .

equipment grounding conductor

A ground rod electrode is always required to be driven into the earth.

False

The grounding electrode network for a lightning protection system is permitted to be used as the grounding electrode system for the electrical service supplying a building or structure only when there are no other electrodes available.

False

A conducting object through which a direct connection to earth is established defines which of the following?

Grounding electrode

What is the maximum resistance to ground permitted for a grounding electrode system consisting of a concrete-encased electrode, a building steel electrode, and a metal water pipe electrodes?

No maximum resistance value is specified in the NEC

If present at each building or structure served, which of the following shall be bonded together to form the grounding electrode system?

I. Concrete-encased grounding electrode

II. Metal in-ground support structures

III. Metal underground water pipe electrode

IV. Rod and pipe electrodes

What is the minimum length of contact that must be made with the earth in order for a metal in-ground support structure to qualify as a grounding electrode?

10'

Where bonding jumpers are used to connect grounding electrodes together to form a grounding electrode system, ? points to the NEC reference used to size such bonding jumpers.

250.53(C)

If present, the structures and structural reinforcing steel described in Section 680.26(B)(1) and (B)(2) are required to be included in the grounding electrode system for a building or structure.

False

A structure is defined as that which is constructed or built and does not include electrical equipment.

True

The minimum sizing requirements for grounded conductors are provided in which of the following?

250.102

A concrete-encased electrode can be created using 20 feet or more of bare copper not smaller than ? .

4 AWG

A concrete-encased grounding electrode can be in a horizontal or vertical orientation as long as there is a minimum ? of contact with the earth.

20'