Grounding connects an electrical system to the earth. Bonding connects metal parts to each other so they stay at the same voltage and give fault current a low-resistance path back to the source. Together they make sure a fault trips the breaker quickly instead of leaving metal enclosures, pipes or structures live and dangerous to touch.
Two different jobs
The words are often used as if they mean the same thing, but they do different work.
| Grounding | Bonding | |
|---|---|---|
| What it connects | The electrical system and equipment to the earth, through grounding electrodes | Metal parts to each other and back to the system's grounding point |
| Main purpose | Limits voltage from lightning, utility surges and accidental contact with higher-voltage lines; stabilizes system voltage to earth | Provides a low-impedance path so fault current trips the overcurrent device fast; keeps touchable metal at the same potential |
| Typical parts | Ground rods, plates, water pipe electrodes, building steel, grounding electrode conductor | Equipment bonding conductors, metal conduit, bonding jumpers, main bonding jumper |
A common misunderstanding is that the earth itself clears faults. It does not. The earth has far too much resistance to carry enough current to trip a typical breaker. Fault current returns to the source through the bonding conductors, and it is that path that lets the breaker or fuse open.
How a ground fault is cleared
- A live conductor touches a metal enclosure, perhaps because of damaged insulation.
- Current flows from the enclosure through the bonding conductor back to the service, where the neutral and ground are connected.
- Because this path has low impedance, the current is high, and the breaker or fuse opens quickly.
- Without a good bonding path, current stays low, the breaker may not trip and the enclosure stays live, waiting for someone to touch it.
The rules
In Canada, grounding and bonding requirements are in the Canadian Electrical Code, Part I (CSA C22.1), which the provinces adopt, in Ontario through the Ontario Electrical Safety Code. The code sets out how systems are grounded, where the neutral is connected to ground, conductor sizes, electrode types and what must be bonded, including metal piping, building steel and equipment. Telecommunications systems have their own bonding requirements, set out in the TIA bonding and grounding standards and coordinated with the electrical code. Check the edition adopted in your province.
What needs to be bonded
- Metal enclosures, raceways and equipment frames
- Metal water piping and other metal piping that could become energized
- Gas piping, as required by the code and the gas utility
- Structural steel where it is used or required to be bonded
- Telecommunications bonding busbars in telecom rooms
- Pools, hot tubs and other wet locations, which have their own detailed rules
- Lightning protection systems, where present, bonded to the electrical grounding system
Common problems found during inspections
- Missing or loose bonding. Bonding jumpers removed during renovations and never replaced, or connections loosened over time.
- Neutral and ground connected in the wrong place. The neutral should be bonded to ground at the service or at a separately derived system such as a transformer, not in downstream panels. Extra connections put normal current on bonding conductors and metal parts.
- Plastic pipe replacing metal. A section of plastic water pipe can break the bonding path the original design relied on.
- Corroded electrodes and clamps. Buried or exposed connections that have corroded or been damaged.
- Isolated ground misunderstandings. "Isolated" ground receptacles still need to be grounded correctly; done wrong, they remove protection.
- Undersized conductors. Bonding conductors smaller than the code requires for the circuit size.
- Telecom grounding missed. Racks and cable trays in telecom rooms not bonded to the telecommunications grounding system. See telecom rooms: the IDF and MDF.
Warning signs. Tingling from metal fixtures or appliances, shocks from water taps, lights that dim or brighten oddly, and breakers that will not trip during a known fault can all point to a grounding, bonding or neutral problem. Stop using the affected equipment and call a licensed electrician.
A typical case
Tenants in a renovated older building report a mild tingle from a metal sink. The renovation had replaced a run of copper water pipe with plastic, which interrupted the metal piping that had been bonded at the service. The sink's metal piping was now isolated from the bonding system. Separately, a contractor had connected neutral and ground together in a downstream subpanel, so some normal return current was flowing on conduit and metal parts.
A licensed electrician removed the incorrect neutral-to-ground connection in the subpanel, installed a bonding jumper to restore continuity of the metal piping, and tested the system. The two problems were unrelated, but each made the other harder to find, and neither would have shown up without someone reporting the symptom. That is why tingling or shocks should always be reported and investigated rather than lived with.
Symptoms and what they can point to
| Symptom | Possible cause | Who should look |
|---|---|---|
| Tingle or shock from metal fixtures, taps or equipment | Missing bonding, a fault on equipment, or neutral current on metal parts | Licensed electrician, promptly |
| Lights dimming or brightening when large loads start | Loose or failing neutral connection | Licensed electrician, promptly |
| Nuisance tripping of ground fault devices | Leakage on equipment, moisture, or neutral and ground mixed downstream | Electrician; engineer if it persists |
| Data or control circuit noise, damaged electronics after storms | Grounding or surge protection problems | Electrical engineer or qualified contractor |
| Green corrosion or broken clamps on piping or electrodes | Deteriorated grounding or bonding connections | Electrician at next maintenance |
Questions to ask after a renovation
- Was any metal water or gas piping replaced with plastic, and was bonding restored where needed?
- Were any new subpanels installed, and are neutral and ground kept separate in them?
- Were bonding jumpers removed to work on meters, water heaters or piping, and were they put back?
- Were new telecom racks and cable trays bonded to the telecom grounding system?
Grounding and power quality
Poor grounding can also cause equipment problems: noise on data and control circuits, nuisance tripping of ground fault devices and damage to electronics during surges. Fixing these issues needs care. Disconnecting a safety ground to cure "noise" is dangerous and against the code. The right fix is a properly designed grounding system, often with surge protection.
Testing
Qualified electrical workers can test grounding systems with ground resistance testers, continuity testers and circuit analyzers. Grounding is also checked during de-energized maintenance, described in switchgear and panel maintenance. In older buildings, see also knob-and-tube and aluminum wiring, since older wiring methods often have no equipment ground at all.
How ehZee can help
Our electrical system inspections look for visible grounding and bonding problems in services, panels, electrical rooms and telecom spaces, alongside the rest of the distribution system. We report what we find and can coordinate testing and corrections with a licensed electrical contractor.
Common questions
Is a three-prong outlet proof that a circuit is grounded?
No. Three-prong receptacles are sometimes installed on circuits with no ground conductor. A simple plug-in tester or an electrician's check will tell you.
Why does the neutral connect to ground only at the service?
So normal return current flows only on the neutral. If neutral and ground are connected in more than one place, some normal current flows on bonding conductors, conduit and metal parts, which is both a shock and a power quality problem.
Can we fix nuisance tripping by removing the ground wire?
No. Removing a safety ground disables the path that lets a fault trip the breaker, leaving metal parts able to become live. Have a licensed electrician find the cause of the tripping instead.