Grounding Terms Definitions - NEC Article 100

Again, we will explain more important definitions included in NEC code Article 100 which will be used along this Course, toady we will show the term “Bonding" Definition.

The terms Bonding & Grounding are often confused or misused. Bonding should not be mistaken for Grounding since their definitions are different as follows:


It is the connection of two or more conductive objects to one another by means of a conductor such as a wire to provide continuity and conductivity.

Grounding / Earthing: 

It is the attachment of a bonded metallic system to earth, typically through ground rods or other suitable grounding electrodes for ensuring zero voltage.

Note: grounding is American standard term is equivalent to earthing which is IEC standard term.

For a Comparison table between bonding and grounding Please review the topic included in
 Understanding NFPA 70(National electrical code) course EC-1 titled NEC Article 100 - Part Three

1- Ground:

The ground is now simply the planet earth.

2- Grounded: 

It means connected to the ground (planet earth), either directly or through a conductive body that extends the ground connection.

3- Grounded Conductor: 

A grounded conductor is the conductor of an electrical system that is intentionally connected to earth via a grounding electrode conductor and a grounding electrode at the service of premises, at a transformer secondary, or at a generator or other source of electric power. It is most commonly a neutral conductor of a single-phase, 3-wire system or 3-phase, 4-wire system but may be one of the phase legs—as in the case of a corner-grounded delta system.

Grounded conductor in different system types:

  • In 3-wire, single-phase systems (see fig.1) the midpoint of the transformer Winding, the point from which the system neutral is derived, is grounded. 

fig (1): 3-wire, single-phase systems

  • For grounded 3-phase, 4-wire wiring systems (see fig.2) the neutral point of the wye-connected transformer(s) or generator is usually the point connected to ground. 

fig (2):  grounded 3-phase, 4-wire wiring systems

  • In delta-connected transformer hookups (see fig.3) grounding of the system can be effected by grounding one of the three phase legs, by grounding a center-tap point on one of the transformer windings (as in the 3-phase, 4-wire “red-leg” delta system), or by using a special grounding transformer which establishes a neutral point of a wye-connection which is grounded. 

fig (3):  delta-connected transformer hookups

The need for a grounded conductor:
  • It limits the voltage upon the circuit that might otherwise occur through exposure to lightning or other voltages higher than that for which the circuit is designed. 
  • It limits the maximum voltage to ground under normal operating conditions. 
  • It provides automatic opening procedure of the circuit if an accidental or fault ground occurs on one of its ungrounded conductors. 

4- Grounding Conductor, Equipment: 
(see fig.4)

Equipment grounding is the intentional electrical interconnection of all metal enclosures that contain electrical wires or equipment with the grounding electrode conductor (all systems) and with the grounded conductor of the system (grounded systems only).

fig (4):  Equipment ground

The term equipment grounding conductor includes bare or insulated conductors, metal raceways [rigid metal conduit, intermediate metal conduit, electrical metallic tubing (EMT)], and metal cable jackets where the Code permits such metal raceways and cable enclosures to be used for equipment grounding—which is a basic Code-required concept.

Equipment grounding function:
  • When the insulation failure occurs on a grounded system, equipment grounding serves to ensure adequate current flow to cause the affected circuit’s over-current protective device to “open,” . This prevents the enclosures from remaining energized, which would otherwise constitute a shock or fire hazard. 

5- Grounding Electrode:

The grounding electrode is any one of the building or structural elements that is in actual physical contact with the earth, such as: see fig.5

  • Metal Underground Water Pipe.
  • Metal Frame of the Building or Structure.
  • Concrete-Encased Electrode.
  • Ground Ring.
  • Rod and Pipe Electrodes.
  • Plate Electrodes.
  • Other Local Metal Underground Systems or Structures (such as piping systems and underground tanks).

fig (5): grounding electrode Types

6- Grounding Electrode Conductor: 
see fig.5

It is the connection between either the grounded conductor of a grounded electrical system (typically the neutral) and the grounding electrode system, or the connection between the equipment ground bus and the grounding electrode system for ungrounded systems.

The conductor that runs from the bonded neutral block or busbar or ground bus at service equipment, separately derived systems, or main building disconnects to the system grounding electrode is clearly and specifically identified as the “grounding electrode conductor.” 

In the next topic, I will continue explaining other definitions from article 100. please, keep following.

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