Quick answer
Electrical bonding is the permanent joining of metal parts, such as boxes, panels, pipes and equipment frames, so they are electrically continuous and conductive, keeping them at the same voltage and giving fault current a low-impedance path back to the source.
The NEC defines bonded as “connected to establish electrical continuity and conductivity.” Bonding, not the ground rod, is what lets a breaker trip fast when a hot wire touches metal.
Quick facts
The key facts about Electrical Bonding, with sources:
Key takeaways
- Bonding joins metal parts so they share one voltage and form a continuous path.
- That path lets fault current return to the source fast enough to trip the breaker.
- The main bonding jumper joins neutral and ground at the service, and only there.
- Metal water and gas piping, including CSST, must be bonded under the NEC.
- Bonding is often confused with grounding; a home needs both.
What bonding means
Bonding means connecting metal parts so electricity can flow freely between them. The NEC Article 100 definition is short: connected to establish electrical continuity and conductivity 1.
In a house, bonding ties together the metal panel, metal boxes, metal conduit, appliance frames, and metal water and gas piping. When everything is bonded, no two metal surfaces you can touch at once should sit at different voltages.
Grounding is a separate idea. It ties the system to the earth. EC&M’s summary of Article 250 puts the difference simply: grounding limits voltages from lightning and surges; bonding joins non-current-carrying metal so fault current has a low-impedance path back to the source and the overcurrent device can clear the fault 2.
How bonding clears a fault
Picture a loose hot wire touching the metal case of a dryer. If the case is bonded, current rushes through the bonding path, the equipment grounding conductor, to the panel.
At the service, the main bonding jumper connects that path to the neutral, which returns to the utility transformer. The current is large, so the breaker trips in a fraction of a second.
If the case is not bonded, it can sit at 120 volts with nothing to trip. A breaker only reacts to current. With no path, there is no current, and the breaker cannot tell anything is wrong. The next person to touch it and a grounded surface completes the circuit.
The same logic covers pipes. A metal water line or gas line can be touched by a damaged cable or appliance. If the pipe is bonded, the fault trips a breaker. If not, the pipe can stay live and anyone touching it and another metal surface is at risk.
IAEI lists three properties of an effective ground-fault current path: electrically continuous, enough capacity, and low impedance 3. Every bonding connection along the way has to meet all three.
- FaultHot wire touches a metal case
- Bonded case and boxCurrent enters the equipment ground
- Equipment grounding conductorCarries current to the panel
- Main bonding jumperJoins ground to neutral at the service
- Back to the transformerHigh current trips the breaker
Kinds of bonding in a home
| Bonding type | What it joins | Code reference |
|---|---|---|
| Main bonding jumper | Neutral bar to ground bar and enclosure at the service | Sized by Table 250.102(C)(1) 2 |
| Equipment bonding | Boxes, raceways and equipment to the equipment grounding conductor | Article 250, Parts V–VII 2 |
| Metal water piping bonding | Interior metal water pipe to the service | NEC 250.104; Part V covers piping 2 |
| Metal gas piping and CSST bonding | Gas piping likely to become energized | NEC 250.104(B); NFPA 54 and maker instructions 5 |
| Pool and spa bonding | Metal parts and water near pools | NEC Article 680 |
Example: sizing jumpers from published IAEI cases
Real worked cases from IAEI Magazine’s sizing article, applied to NEC tables 4. Your installation may differ.
| Situation | Table used | Minimum bonding size |
|---|---|---|
| 250 kcmil copper service conductors | Table 250.102(C)(1) | 2 AWG copper or 1/0 AWG aluminum |
| Three 250 kcmil copper per phase (750 kcmil) | Table 250.102(C)(1) | 2/0 AWG copper or 4/0 AWG aluminum |
| Four circuits (20, 30, 50, 60 A) in one raceway | Table 250.122 | One 10 AWG equipment grounding conductor, sized from the 60 A device |
| Gas piping bonding jumper | Table 250.122 | Not smaller than the equipment grounding conductor of the supplying circuit 5 |
These are illustrations of how the tables work, not a design for your home. An electrician sizes bonding from the actual conductors and the edition in force.
Where you can see bonding
Near the water heater or where the water line enters, you may see a copper wire clamped to the pipe. A similar clamp may be on the gas line.
Inside the main panel, a green screw or strap joins the neutral bar to the metal can; that is the main bonding jumper.
In a panel fed from the main (a subpanel), neutral and ground bars are kept separate.
IAEI notes that bonding connections are required to be accessible 5, so a clamp should not be buried in a finished wall.
Our grounding and bonding guide shows how the pieces fit together at a typical house.
- 7Approved connection methods in NEC 250.8, plus other listed meansEC&M
- 10Parts in NEC Article 250; Part V is bondingEC&M
- 1Place neutral and ground are bonded: the service or first disconnect
Source: [2]
What bonding protects against
Limits of bonding
Bonding needs every link to be sound. A loose locknut, corroded clamp or painted-over connection adds impedance and slows the breaker. OSHA’s grounding guide notes that bonding conductors must be able to safely carry any fault current imposed on them 6.
Bonding also cannot catch small leakage currents through a person. Catching that leak is the job of ground-fault protection.
Bonding is not grounding
Bonding joins metal parts to each other and back to the source. Grounding joins the system to earth. A ground rod without good bonding will not trip a breaker in a fault.
What drives the cost of bonding work
We do not print prices. Adding a missing water or gas bond is usually a small job. Correcting a panel where neutral and ground are mixed downstream, or bonding a pool, takes more time. Access and permit needs drive the cost. See the project cost tool and our electrical inspection service.
How an electrician verifies bonding
Bonding work is for licensed electricians, often under permit.
- Check the main bonding jumper at the service.
- Check that neutral and ground are separate in every subpanel.
- Confirm water and gas piping bonds, and CSST bonding per the maker’s instructions 5.
- Tighten or replace corroded clamps; keep connections accessible.
- Test continuity from outlets and equipment back to the panel.
Owner checks
- Look, without touching, for loose or corroded clamps on water and gas lines.
- After plumbing work, ask whether any bonding jumper was removed.
- After remodeling, make sure bonding clamps were not buried behind drywall 5.
- If you have yellow-jacketed CSST gas tubing, ask an electrician to confirm it is bonded.
Warning signs
A tingle from a faucet, shower or appliance; a cut bonding wire after plumbing work; or a breaker that will not trip when an appliance case is clearly faulted are serious signs. So is unbonded CSST in a lightning-prone area.
Shock from metal is an emergency
If a faucet, appliance or metal fixture shocks you, stop using it and turn off the circuit if you know which breaker. Call an electrician. If someone is injured, call 911 and do not touch them while they may be in contact with the source.
Code rules
Bonding is NEC Article 250, Part V. Section 250.8 lists seven approved connection methods plus other listed means; Table 250.102(C)(1) sizes main and supply-side bonding jumpers 2.
Section 250.104(B) covers metal gas piping, including CSST; the bonding jumper may connect to the service enclosure, the grounded conductor at the service, the grounding electrode conductor if sized properly, or the electrodes, and its attachment points must be accessible 5.
NFPA 54, the National Fuel Gas Code, requires CSST maker instructions to be followed, and some are stricter than the NEC 5. Local adoption varies.
Bonding compared with related terms
| Term | What it does | Relation to bonding |
|---|---|---|
| Grounding | Connects the system to earth | Works alongside bonding; does not clear faults alone |
| Equipment grounding conductor | Wire or raceway back to the panel | The main bonding path for each circuit |
| Neutral | Carries normal return current | Bonded to ground only at the service |
| Ground fault | Hot touching metal or ground | The event bonding is designed to clear |
Myths about bonding
- Myth Bonding and grounding are the same thing.
- Reality Bonding joins metal parts; grounding connects to earth 2.
- Myth Neutral and ground should be joined in every panel.
- Reality Only at the service or first disconnect; separate everywhere downstream.
- Myth Plastic water pipe means no bonding is needed.
- Reality Gas piping and any metal sections still need attention; ask an electrician.
- Myth Any wire will do for a bond.
- Reality Bonding jumpers are sized from NEC tables 4.
State code and gas rules
When to get bonding checked
Bonding is invisible until it matters. Ask for a check in these cases.
- If Any tingle from metal fixtures
- Then Call an electrician now
- If New plumbing or water heater
- Then Confirm water and gas bonds were restored
- If CSST gas tubing in the home
- Then Confirm it is bonded per the maker’s instructions
- If Adding a subpanel, pool or hot tub
- Then Expect bonding work in the permit scope
One visit
Ask for grounding, bonding and GFCI checks together during an electrical safety visit.
Questions about Electrical Bonding
What is the difference between bonding and grounding?
Bonding joins metal parts together and back to the source so they share one voltage and give fault current a low-impedance path. Grounding connects the system to the earth to limit voltage from lightning and surges. A safe home needs both.
Why is bonding important?
Without it, a fault can leave a metal case or pipe live without tripping the breaker. Bonding gives fault current a path back to the source, so the breaker trips quickly and metal parts stay at the same voltage.
What is a main bonding jumper?
It is the connection, often a green screw or strap, that joins the neutral bar to the ground bar and metal enclosure at the service. It is the one place neutral and ground are joined. It is sized from NEC Table 250.102(C)(1).
Do I need to bond my water pipes?
Metal water piping must be bonded under the NEC. An electrician checks the size and location of the bond. If parts of your plumbing were replaced with plastic, ask whether the bonding still works.
Does gas pipe need to be bonded?
Metal gas piping likely to become energized must be bonded under NEC 250.104(B). CSST, the flexible yellow-jacketed tubing, has extra bonding rules in NFPA 54 and its maker’s instructions because lightning can damage it.
Should neutral and ground be bonded in a subpanel?
No. Neutral and ground are bonded only at the service or first disconnect. In a subpanel they must be separate so normal neutral current does not flow on ground wires and metal parts.
What happens if a house is not bonded properly?
A fault could leave metal parts energized without tripping the breaker, creating a shock risk. Different metal systems could sit at different voltages. An electrician can test and correct it.
Can bonding wires be hidden in walls?
Bonding connections to gas and water piping must be accessible, so the clamp should not be sealed behind finished walls. The wire run itself can be concealed where the code allows.
Is pool bonding the same as house bonding?
It follows the same idea but has its own rules in NEC Article 680, including bonding metal parts and the water near pools and spas. It is specialist work for an electrician.
How do I know if my house is bonded?
Look for clamps and copper wires on the water and gas lines near where they enter. Do not touch them or open the panel. An electrician can confirm the main bonding jumper and test continuity.
Sources
- Mark Lamendola, EC&M, Understanding NEC Definitions for Grounding (May 2024), retrieved .
- Randy Barnett, EC&M, 10 Sure Ways to Tell the Difference Between Bonding & Grounding (Aug 2022), retrieved .
- Michael Johnston, IAEI Magazine, Equipment Grounding for Safety (2008), retrieved .
- L. Keith Lofland, IAEI Magazine, Sizing of Conductors Related to Grounding & Bonding (March 2021), retrieved .
- Michael Johnston, IAEI Magazine, Bonding Metal Gas Piping (2009), retrieved .
- OSHA Construction eTool, Electrical Incidents: Grounding, retrieved .
- Texas Department of Licensing and Regulation, 2023 National Electrical Code is almost here, retrieved .
- Washington State Register WSR 25-23-069 (L&I adopts the 2026 NEC), retrieved .
Expert review
Written by the HyreElectrical Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Definitions follow EC&M’s 2024 NEC definitions column; Article 250 structure, 250.8 and Table 250.102(C)(1) follow EC&M; fault path properties and sizing cases follow IAEI Magazine; gas and CSST bonding follow IAEI’s 2009 article. No DIY wiring; no prices under G-COST.
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