"Earthing" and "bonding" are used almost interchangeably in casual conversation, and on many job sites, the two words get treated as synonyms. They aren't. They serve different protective functions, and confusing them leads to installations that look correctly wired but leave a genuine safety gap. This guide draws a clear line between the two.
What Earthing Does
Earthing connects an installation — specifically, the exposed metal parts of electrical equipment that aren't meant to carry current in normal operation — to the general mass of the earth via an earth electrode. Its job is to give fault current somewhere safe to go: if a live conductor comes into contact with equipment casing, earthing provides a low-resistance path back to the source, allowing enough current to flow to trip the protective device quickly, rather than leaving the casing permanently live at a dangerous voltage.
What Bonding Does
Bonding connects separate metal parts — pipework, structural steel, cable trays, equipment enclosures — to each other electrically, so that they are all held at (approximately) the same electrical potential. Bonding does not necessarily connect anything to earth at all; its purpose is to eliminate potential difference between metal parts that a person could simultaneously touch. If two metal objects a person could touch are bonded together, even if a fault raises both their potentials, there's no dangerous voltage between them — which is what actually causes a shock through the body.
A simple way to hold the distinction
Why an Installation Needs Both
| Earthing | Bonding | |
|---|---|---|
| Connects | Equipment/system to the general mass of earth | Separate metal parts to each other |
| Primary purpose | Provide a return path for fault current, enabling protective devices to operate | Eliminate touch-voltage between simultaneously accessible metal parts |
| Tested with | An earth resistance tester (fall-of-potential or clamp-on method) | Continuity test between bonded points — very low resistance expected |
| Typical scope | Main earth electrode, sub-mains, individual circuit protective conductors | Water pipes, gas pipes, structural steel, extraneous conductive parts, equipment enclosures |
How Each Is Verified in the Field
Earthing is verified with an earth resistance test — measuring the actual resistance from the earth electrode to true earth, using the 3-point fall-of-potential method or a clamp-on tester, and comparing against the accepted limit for the installation type. Bonding is verified differently: as a continuity check between the bonded points, confirming a very low resistance connection exists — the concern isn't "how many ohms to earth" but simply "is this connection solid and unbroken." See our earth resistance testing guide for the earthing test procedure in detail.
CIE manufactures the CIE/222M and DET-2000 earth resistance testers, and our multimeters handle the continuity checks bonding verification requires. Contact us for guidance on testing either.