Grounding and Bonding Explained: Electrical Basics
Chameera Sampath · 10/18/2026
Grounding vs bonding: equipment grounding conductors, why earth does not clear faults, the grounding electrode system and the single neutral-to-ground bond.
Grounding and bonding are two related but distinct parts of an electrical system. Grounding connects the system to the earth. Bonding connects metal parts together so that they stay at the same voltage and provide a low-impedance path for fault current back to its source. It is bonding, not the earth, that makes a breaker trip when a hot conductor touches metal.
Quick answer. Grounding: a connection to earth, through ground rods, a concrete-encased electrode or a metal water pipe, which limits voltage from lightning and utility surges. Bonding: connecting all metal parts and the equipment grounding conductors back to the neutral at the service, so that a fault draws enough current to trip the breaker quickly. Neutral and ground are bonded at one point only: the service (or a separately derived system).
Definitions
| Term | Meaning |
|---|---|
| Grounded | Connected to earth or to a conductive body that extends the earth connection |
| Grounded conductor | The neutral, a current-carrying conductor intentionally connected to earth at the service |
| Equipment grounding conductor (EGC) | The bare or green wire that connects metal boxes, enclosures and equipment frames back to the service; it carries current only during a fault |
| Bonding | Connecting conductive parts to establish electrical continuity and conductivity |
| Main bonding jumper | The connection between the neutral and the equipment grounding system at the service |
| Grounding electrode | The conductor in contact with the earth: ground rod, concrete-encased electrode, metal water pipe |
| Grounding electrode conductor (GEC) | The wire from the service to the grounding electrode |
Why bonding clears faults, and earth does not
When a hot conductor touches a metal box, current needs a low-impedance path back to the source to rise high enough to trip the breaker. The equipment grounding conductor provides that path: through the box, back along the EGC to the panel, across the main bonding jumper to the neutral, and back to the utility transformer.
The earth is a poor conductor. A ground rod typically has a resistance to earth measured in ohms or tens of ohms. Using Ohm's law, a 120 V fault through 25 Ω of earth would draw only about 4.8 A, far too little to trip a 20 A breaker, leaving the faulted metal energized. That is why the code does not permit the earth to serve as the fault-current path, and why the EGC must run with the circuit conductors. The Ohm's law calculator shows the arithmetic.
What grounding to earth does
Connecting the system to earth through the grounding electrode limits the voltage imposed by lightning, line surges and accidental contact with higher-voltage lines, and stabilizes the system voltage to earth during normal operation. It works together with surge protection; see surge protector vs power strip.
The grounding electrode system
At a house, the grounding electrode system typically includes some combination of:
- Ground rods, usually 8 feet long. A single rod that cannot be shown to have 25 Ω or less resistance to earth must be supplemented by a second electrode, commonly a second rod at least 6 feet away.
- A concrete-encased electrode (often called a Ufer ground): reinforcing steel or bare copper in the footing.
- A metal underground water pipe in contact with earth for at least 10 feet, which must be supplemented by another electrode.
All electrodes present at a building are bonded together.
One neutral-to-ground connection
The neutral and the equipment grounding conductors are connected together at one point: the service disconnect, through the main bonding jumper. In a subpanel, the neutrals and grounds must be on separate, isolated bars, and the subpanel is fed with four wires (two hots, neutral and ground). Bonding neutral to ground in a subpanel puts normal neutral current onto equipment grounding conductors, metal raceways and water pipes, which is a shock and fire hazard.
A transformer that creates a new neutral, such as a 480 V to 208Y/120 V unit, is a separately derived system and gets its own neutral-to-ground bond; see the transformer sizing guide.
Bonding other metal systems
The code requires metal water piping and other metal piping systems likely to become energized, including gas piping in many cases, to be bonded to the service grounding system. Bonding keeps them at the same potential as the electrical system, so a fault cannot leave a pipe energized relative to nearby grounded metal.
Sizing grounding conductors
Equipment grounding conductors are sized according to the rating of the overcurrent device protecting the circuit, and grounding electrode conductors according to the size of the service conductors, using tables in Article 250 of the National Electrical Code. Equipment grounding conductors often must be increased in size when the circuit conductors are increased for voltage drop.
Common mistakes
- Bonding neutral and ground in a subpanel.
- Relying on a ground rod alone, without an equipment grounding conductor, to protect equipment.
- Replacing two-prong receptacles with three-prong receptacles without a ground conductor.
- Leaving metal water piping unbonded after a plumbing repair with plastic pipe.
- Removing the grounding pin from a plug.
Frequently asked questions
What is the difference between grounding and bonding? Grounding connects the electrical system to the earth. Bonding connects metal parts together and to the equipment grounding conductors so that fault current returns to its source and trips the breaker.
Why are neutral and ground connected at the main panel? That single connection, the main bonding jumper, gives fault current on the grounding conductors a path back to the source through the neutral. Making it at only one point keeps normal neutral current off the grounding conductors.
Does a ground rod make a house safe on its own? No. The ground rod limits surge and lightning voltages. Protection against shock from faults depends on equipment grounding conductors and bonding back to the service.
What color is the ground wire? Green, green with yellow stripes, or bare copper; see the wire color code.
Scope
This article describes grounding and bonding for residential systems in the United States under Article 250 of the National Electrical Code. Grounding and bonding work should be carried out by a licensed electrician.
Written by Chameera Sampath. Not yet reviewed by a licensed electrician — see the methodology page. To report an error, use the contact page.