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.
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.