Grounding vs Bonding and Bonding vs Grounding - What Are They?

[jar546]

It's been getting a little old arguing the differences between these over the years, so I thought I would put this together to see if this helps to clarify a few things. Let's start with definitions and meanings. I am using the 2023 NEC, technically known as the NFPA 70.

Grounded (Grounding).
Connected (connecting) to ground or to a conductive body that extends the ground connection.

Ground.
The earth

Bonded (Bonding).
Connected to establish electrical continuity and conductivity.

Bonding Conductor or Jumper.
A reliable conductor to ensure the required electrical conductivity between metal parts required to be electrically connected.

Either of the two terms bonding conductor or bonding jumper may be used. The term bonding jumper is sometimes interpreted to mean a short conductor, although some bonding jumpers may be several feet in length. The primary purpose of a bonding conductor or jumper is to ensure electrical conductivity between two conductive bodies, such as between a box and a metal raceway. Bonding jumpers are particularly important where a box has either concentric- or eccentric-type knockouts. These knockouts can impair the electrical conductivity between metal parts and may actually introduce unnecessary impedance into the grounding path.

Bonding Jumper, Equipment.
The connection between two or more portions of the equipment grounding conductor.

Equipment bonding jumpers ensure that an effective ground-fault current path is not compromised by an interruption in mechanical or electrical continuity. For example, conduits entering an open-bottom switchboard are usually not mechanically connected to the switchboard. Expansion fittings may not provide electrical continuity because they are loosely joined raceways. Bonding jumpers are necessary in order to provide electrical continuity.

Essentially, the purpose of grounding is to connect electrical systems to the earth. The purpose of bonding is to connect electrical equipment and components. The two are integral to each,....well, for the most part. You need bonding to have grounding.

250.4(A)(1) Electrical System Grounding.
Electrical systems that are grounded shall be connected to earth in a manner that will limit the voltage imposed by lightning, line surges, or unintentional contact with higher-voltage lines and that will stabilize the voltage to earth during normal operation.

250.4(A)(3) Bonding of Electrical Equipment.
Normally non–current-carrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected together and to the electrical supply source in a manner that establishes an effective ground-fault current path.

Grounding is to stabilize a system by establishing a path to ground, the same ground the utility uses when it generates power. This helps to stabilize voltages during lightning events, surges, or short circuits with power lines. Bonding helps to facilitate the operation of overcurrent protection devices (OCPD) such as fuses and circuit breakers during short circuit events.

I hope this helps.

 

[e hilton]

How about a sketch.

 

[jar546]

How about a sketch.

I'm not an artist and don't want to use copyrighted material. I would love to be able to do this.

 

[e hilton]

If you give credit to the source, is it a copywrite violation?

I was hoping for examples of what is and whats not.

 

[jar546]

How about a sketch.

 

[jar546]

Although frequently used interchangeably in the field, the terms grounding and bonding are separate concepts that have different outcomes based on the requirements of Article 250. The two concepts are not mutually exclusive though, and in many cases a single physical action, such as connecting the equipment grounding conductor (EGC) to the grounding terminal of a duplex receptacle, results in a bonding, as well as a grounding, connection.

 

[wwhitney]

My approach to thinking about this (with NEC terms in parentheses):

The term "grounding" is overloaded and used to mean two distinct things: bonding and earthing. "Bonding" is electrically connecting metal parts in the context described below. "Earthing" is connecting to the earth.

The basic goal here is to prevent nearby surfaces from being at different electrical potentials, which would present a shock hazard to anyone touching both surfaces. So all the exposed metal parts of an electrical system are required to be bonded to each other (via the Equipment Grounding Conductor, or EGC). This ensures that these parts will have little or no potential difference between them. People may also be in contact with the earth, so a system of earth electrodes (the Grounding Electrode System, consisting of Grounding Electrodes connected by Bonding Jumpers) is created and connected (via the Grounding Electrode Conductor) to these bonded metal parts so they are all at earth potential.

In an "ungrounded" electrical supply system, this is almost the end of the story. The actual circuit conductors have no connection to earth, and so have an undefined voltage relative to earth. If one of the circuit conductors faults to the earth or to the bonded metal parts, the only change is that now the circuit conductors all have a well defined voltage relative to earth; effectively it becomes a "grounded" system as per below.

If a different circuit conductor also faults to the bonded metal parts or to earth, now current will flow; if both faults are to the bonded metal parts, enough current should flow to trip an overcurrent device. But if one of the faults is to the actual earth, then generally that earth connection resistance is high enough that for typical utilization voltages (<1000V), the current flow will not be sufficient to trip an overcurrent device. This is one reason that any ungrounded electrical system requires a system of ground detectors, which provide a visual signal in the event of the first fault. Maintenance staff are supposed to monitor the ground detectors, and in the event of an earth fault, find and fix it, hopefully before a second fault occurs.

In the far more common case of a grounded electrical system, the first fault above is made intentionally. One conductor (Grounded Conductor) is connected to the bonded metal parts via a jumper (Main Bonding Jumper for a service, System Bonding Jumper for a Separately Derived System). As this is a low impedance connection, now the fault of any other circuit conductor to the bonded metal parts should flow enough current to trip an overcurrent device. Faults to the actual earth can still flow low enough current not to trip an overcurrent device, but enough current to potentially be a hazard to people next to the fault.

Cheers,
Wayne

 

[jar546]

While often used synonymously in practice, 'grounding' and 'bonding' are distinct concepts with different purposes as outlined in Article 250. However, these concepts are not mutually exclusive. In numerous instances, a single action can achieve both objectives. For example, when you connect the equipment grounding conductor (EGC) to the grounding terminal of a duplex receptacle, this act simultaneously establishes both a bonding and a grounding connection.