Bonding vs Grounding: What the 2023 NEC Actually Requires

The 2023 edition of the National Electrical Code (NEC) continues to refine these concepts, aiming for greater clarity and safety. Understanding what the code actually requires is essential for protecting lives, property, and your professional reputation. This isn’t just about passing an inspection—it’s about upholding the highest standards of safety in our trade.

The Fundamental Difference: Safety from Faults vs. Stability

At its core, the distinction between grounding and bonding comes down to two different jobs:

• Grounding: This is the intentional connection of an electrical system to the earth. Its primary purpose is to protect against overvoltages from lightning, line surges, or accidental contact with higher-voltage systems. Think of it as providing a safe path for massive, unpredictable energy to dissipate into the ground.
• Bonding: This is the permanent joining of all normally non-current-carrying metallic parts of a system—conduit, enclosures, equipment frames—to form a continuous, low-impedance path. Its primary job is to provide a clear road for fault current to travel back to its source, which allows the overcurrent protective device (breaker or fuse) to operate almost instantly. It also minimizes hazardous potential differences between conductive parts, creating an equipotential plane as required by NEC 250.4(A)(4). This is the very definition of an effective ground-fault current path.

A common and dangerous misconception is that the earth itself can serve as this fault-clearing path. The NEC is explicit: the earth is not considered an effective ground-fault current path because its impedance is far too high to allow enough current to flow to trip a standard breaker. That’s why bonding is so critical.

Grounding Deep Dive: The Connection to Earth

The grounding system is your installation’s defense against external electrical threats. It’s designed to stabilize the system’s voltage with respect to the earth. The key components here are:

• Grounding Electrode System: This is the physical connection to the earth. It can be a combination of metal underground water pipes, the metal frame of a building, concrete-encased electrodes, ground rings, or ground rods. A supplementary electrode, like a ground rod, is required by NEC 250.53(D)(2) when using a water pipe as the primary electrode.
• Grounding Electrode Conductor (GEC): This is the wire that connects the system’s grounded conductor (usually the neutral at the service) to the grounding electrode system. The GEC’s job is to carry current to the earth only under specific conditions, like a lightning strike. It is not intended to carry current during a typical ground fault.

Bonding Deep Dive: Creating the Path to Safety

If grounding is about stabilizing voltage, bonding is all about clearing faults. When an ungrounded (hot) conductor touches a metal frame, the bonding system ensures that the fault current has an easy, low-resistance journey back to the source. This surge in current is what trips the breaker. Without a proper bonding path, that metal frame simply becomes energized, creating a severe shock hazard.

The essential players in the bonding system include:

• Equipment Grounding Conductor (EGC): This is the path that connects all the metal parts of your installation back to the service or source. It can be a wire, or it can be the metallic raceway itself (like RMC or EMT). An EGC is sized based on the overcurrent device protecting the circuit, as found in NEC Table 250.122. For more on this, our lesson on how to ground non-grounding switches and receptacles provides practical examples.
• Main Bonding Jumper (MBJ): At the service entrance, the MBJ creates the critical link between the grounded conductor (neutral) bus and the equipment grounding conductor bus. This connection ensures that fault current from the EGC can get back to the system neutral and return to the source transformer.
• System Bonding Jumper: In separately derived systems, like a transformer, this jumper serves the same function as an MBJ. It connects the system’s newly created grounded conductor to the equipment grounding system. Per NEC 250.30(A)(1), this connection must be made at only one point to prevent objectionable current from flowing on grounding conductors during normal operation.

Key Focus Areas in the 2023 NEC

The 2023 NEC introduces several clarifications and changes that every electrician must know regarding grounding and bonding.

Separately Derived Systems (NEC 250.30)

Properly bonding separately derived systems remains a major point of emphasis. When a transformer creates a new system, you must establish a new ground reference. This involves installing a system bonding jumper and often a grounding electrode conductor to a local grounding electrode. A critical component in this setup is the supply-side bonding jumper, which ensures the fault current path remains intact between the source of the derived system and the first disconnecting means, especially when they are in separate enclosures. For a deeper dive, explore our guide on transformer grounding and bonding rules in the 2023 NEC.

Intersystem Bonding Termination (NEC 250.94)

The 2023 NEC continues to mandate an intersystem bonding termination (IBT) for connecting other systems like cable TV, satellite, and telephone. The IBT must be located externally at the service equipment or disconnecting means. This provides a safe and accessible point for other trades to bond their systems, preventing voltage differences that could pose a hazard or damage sensitive electronics.

Connection Methods and Objectionable Current

The code emphasizes durable and reliable connections. Methods like exothermic welding or using irreversible compression-type connectors are explicitly recognized for their reliability, especially for GEC connections that might be concealed or inaccessible, and are permitted per NEC 250.8(A). The concept of objectionable current—current flowing on grounding paths during normal operation—is also a key concern addressed by proper bonding. This dangerous condition is often caused by improper neutral-to-ground connections on the load side of the main bonding jumper, creating parallel paths for neutral current to travel on EGCs and metal piping.

Putting It All Together for a Safer Installation

With the electrical industry’s constant evolution comes an even greater responsibility to get the fundamentals right. Mastering the nec 2023 grounding and bonding requirements isn’t just about following rules; it’s about understanding the “why” behind them. Grounding protects from external events, while bonding protects from internal faults. Together, they form a complete safety system that is the foundation of every safe electrical installation.

The complexities of Article 250 require continuous learning. To stay current and ensure your installations are safe, compliant, and efficient, it’s vital to invest in your education. Browse our courses at ExpertCE to find state-approved continuing education that covers the latest NEC changes and reinforces these critical safety concepts.

Frequently Asked Questions (FAQ)

What is the main difference between a Grounding Electrode Conductor (GEC) and an Equipment Grounding Conductor (EGC)?

A GEC connects the system’s grounded conductor to the earth via the grounding electrode system for lightning and surge protection. An EGC connects the metal parts of equipment back to the source to create a path for fault current to trip a breaker. The EGC is the backbone of the effective ground-fault current path.

Why is “objectionable current” a problem?

Objectionable current means that under normal, non-fault conditions, current is flowing on conductors and equipment (like EGCs, metal pipes, or enclosures) that should not be carrying current. This is typically caused by incorrect bonding, such as multiple neutral-to-ground bonds, creating a shock hazard and potential fire risk.

Can I use the earth as the path for fault current to return to the source?

No. NEC 250.4(A)(5) explicitly states that the earth shall not be considered an effective ground-fault current path. The impedance of the earth is too high to allow the large amount of current needed to operate an overcurrent protective device quickly.