Grounding and bonding
What you’ll learn
- The difference between grounding (to earth) and bonding (metal tied together).
- Why a ground rod alone will not trip a breaker, with the arithmetic.
- How a bonded fault path clears a fault in a fraction of a second.
- Why neutral and ground are joined at one point only.
- The CEC and NEC names for the same conductors.
Grounding and bonding are two different jobs that people blur into one word. Grounding connects the electrical system to the earth. Bonding ties all the metal that isn’t supposed to carry current together and back to the source, so that a fault trips the breaker. Most shocks from metal enclosures happen when someone trusted the first to do the second’s job.
Grounding: connecting to earth
At the service, the system is connected to a grounding electrode — a rod, a buried conductor, a metal water pipe, the building steel or the rebar in the footing, depending on what is there and what your code accepts. That connection:
- holds the system’s voltage close to earth, so a 120 V conductor is about 120 V to the floor you stand on;
- gives lightning, utility surges and a fallen higher-voltage line a path into the earth.
What it does not do is carry enough current to trip a breaker. The earth is a poor conductor, and the path through it back to the utility’s transformer has far too much resistance.
Bonding: the fault path
Bonding connects every metal part that could become live — boxes, enclosures, conduit, appliance cases, metal piping — to each other and back to the source through a path of low resistance: the bonding conductor (the bare or green one in a cable), metal raceway, and the connection to the neutral at the service. When a hot conductor touches bonded metal, current rushes back along that path, far more than the breaker’s rating, and the breaker or fuse opens in a fraction of a second. The metal is only live for that instant.
Worked: why the earth can’t do bonding’s job
- A 120 V hot conductor touches a metal case. The breaker is 15 A.
- Case connected only to a ground rod; total path through the earth back to the source 20 Ω (a practice number): I = 120 ÷ 20 = 6 A. Less than 15 A — the breaker holds, and the case sits at a dangerous voltage.
- Case properly bonded; the whole fault loop is 0.2 Ω (practice number): I = 120 ÷ 0.2 = 600 A — forty times the breaker’s rating. It trips at once.
- Same fault, same voltage. The only difference is the path — and that is what bonding is.
Neutral and ground meet at one point
The neutral (the grounded conductor) and the bonding system are joined together at one place — generally at the service equipment, by the main bonding jumper. That joint is what gives a fault on bonded metal its path back to the source. Everywhere downstream, they are kept apart: the neutral carries the normal return current, and the bonding conductors carry nothing unless there is a fault. Join them again in a subpanel or a receptacle and normal current starts flowing on the metal. The exact arrangement for services, separate buildings and generators is in your code book.
The same conductors, two books
| What it does | CEC (CSA C22.1) usually says | NEC usually says |
|---|---|---|
| The bare or green conductor to equipment | bonding conductor | equipment grounding conductor (EGC) |
| Conductor from the service to the electrode | grounding conductor | grounding electrode conductor (GEC) |
| The current-carrying conductor tied to earth (usually the neutral) | grounded conductor / identified conductor | grounded conductor |
| The neutral-to-enclosure link at the service | bonding jumper | main bonding jumper |
Try one: a 240 V fault through 30 Ω of earth
I = 240 ÷ 30 = 8 A. On a 30 A circuit, nothing trips. Bonded, with a 0.25 Ω loop: 240 ÷ 0.25 = 960 A — it trips.
On the job
Tips from the job
- Treat every bonding connection like a current-carrying one: clean metal, tight, the right fitting. It only works if it works on the worst day.
- Know the names in both books. The CEC says “bonding conductor” where the NEC says “equipment grounding conductor” — you will read both on the same job.
- When you see the neutral bar and the ground bar bonded in a subpanel, stop and ask. Whether it belongs depends on the installation and your code.
- Paint, powder coat and anodising are insulators. Bonding to painted metal needs a fitting or a scrape that reaches bare metal.
Common mistakes
- Thinking “it’s grounded” means “it’s safe”. Earth alone can’t carry enough fault current to trip a breaker.
- Using the bonding conductor as a neutral, or the neutral as a bond.
- Bonding neutral to ground a second time downstream of the service.
- Leaving a bonding jumper off a flexible or non-metallic section, so the metal after it is not bonded.
Check yourself
7 questions. Tap an answer — it is marked straight away and the reason opens under it. Get 80% or better and the lesson is ticked off on the year page.
Not started yet.
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What is the main job of bonding?
Answer and why
B. Bonding joins all the non-current-carrying metal into one low-resistance path back to the source. When a hot conductor touches that metal, a big fault current flows and the protection opens fast.
-
What is the main job of grounding (connecting to earth)?
Answer and why
C. The grounding electrode ties the system to the earth, which steadies its voltage to earth and gives lightning, surges and contact with higher-voltage lines somewhere to go. It is not what trips a breaker.
-
A 120 V hot touches a metal case that is connected ONLY to a ground rod, with 20 Ω through the earth back to the source. About how much fault current flows?
Answer and why
A. I = V ÷ R = 120 ÷ 20 = 6 A. That won’t trip a 15 A breaker — the case just sits live. The earth is not a good fault path.
-
The same fault with the case properly bonded, and a total fault loop of 0.2 Ω. About how much current?
Answer and why
C. I = 120 ÷ 0.2 = 600 A. That is many times the breaker’s rating, so it opens almost instantly. That is the whole point of bonding.
-
In a typical service, where are the neutral and the bonding (grounding) system connected together?
Answer and why
D. The neutral and the bonding system are joined at one point, generally at the service equipment. Joining them again downstream puts normal neutral current on the bonding conductors and metal. Check your code book for the details of your installation.
-
Does the bare or green conductor normally carry current?
Answer and why
B. The equipment bonding / grounding conductor carries current only when something has gone wrong. The neutral is the normal return path.
-
The CEC usually calls the green or bare conductor to a device a…
Answer and why
A. In CEC language it is a bonding conductor; in the NEC the same conductor is an equipment grounding conductor. Same job, different name — know both.
Questions people ask
If the earth is a poor fault path, why ground at all?
Because grounding solves a different problem. Lightning, a surge on the utility lines, or a high-voltage line falling onto a low-voltage one all push the system’s voltage far above earth. Connecting to earth gives that energy somewhere to go and holds the system close to earth potential. Clearing an ordinary fault is bonding’s job.
Why can’t the neutral and ground be joined in every panel?
The neutral carries normal return current all the time. If it is joined to the bonding system in more than one place, some of that current splits off and flows home on the bonding conductors, conduit and enclosures instead — metal that should carry nothing. That is a shock and noise hazard. So they are joined at one point, generally the service, as your code directs.
Related
- Bonding vs grounding — the short glossary version.
- Hot, neutral, ground — press the fault and watch the bond do its job.
- Boxes, devices and terminations — the lesson before this one.
- Basic residential circuits — the next lesson.
- Services and panels — where the one neutral-to-ground connection lives.
- All first year lessons
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