By You can install a perfect earthing electrode and still be unable to prove it works — unless there’s an earthing test link in the circuit. This small, often-overlooked component is what lets you measure earth resistance without digging up the electrode. Here’s what it is, where it goes, and why inspectors look for it.
What is an earthing test link?
An earthing test link (also called a test joint or disconnecting link) is a bolted metal link — usually a gunmetal, brass or GI strip — that connects the earth electrode to the earthing conductor going to the main earth bar. It sits inside the earth pit chamber and can be unbolted to physically separate the electrode from the rest of the earthing network.
That single feature is the whole point: to measure an individual electrode’s resistance accurately, you must isolate it from every other earth path. The test link is the isolation point.
Why every earth pit needs one
Without a test link, all your earth electrodes are permanently tied together through the earth bar. An earth-resistance tester would then read the combined network, not the pit you care about — you’d never know a single electrode had gone bad. The test link lets you:
- Disconnect one electrode and measure it on its own.
- Verify each pit at commissioning and during periodic testing.
- Isolate faults — find the pit that has drifted out of spec.
- Satisfy inspection — electrical inspectors and audits expect a testable earth.
See earthing test links and accessories → Earthing Accessories
Where the test link is fitted
The test link lives inside the earth pit chamber cover at ground level, bolted between the electrode terminal and the outgoing earth strip/cable. Keeping it in an accessible chamber means testing takes minutes and no excavation — just lift the chamber lid, unbolt the link, connect the tester, and re-bolt afterwards.
Related → Earth Pit Chamber Cover
How to test earth resistance through a test link
The typical field method is the fall-of-potential (three-point) test:
- Open the earthing test link to isolate the electrode under test.
- Connect the earth tester’s electrode terminal to the isolated electrode.
- Drive the two auxiliary spikes (potential and current) in a straight line away from the pit.
- Read the resistance; compare against the design limit (commonly ≤5 Ω for general earthing and ≤10 Ω for lightning earthing, subject to the applicable standard).
- Re-bolt the test link so the electrode is back in the network before you leave.
If a reading is high, the fix is usually adding backfill compound, driving a parallel electrode, or replacing a corroded joint — not ignoring it.
Material matters
A test link carries fault current when bolted, so it needs to be corrosion-resistant and mechanically solid. Gunmetal/brass and hot-dip galvanised links hold up far better than a bare mild-steel strip that rusts and raises joint resistance over time — which would defeat the purpose.
Frequently asked questions
What is an earthing test link used for?
To isolate a single earth electrode so its resistance can be measured accurately, without the reading being masked by other electrodes in the network.
Where is the test link located?
Inside the earth pit chamber at ground level, bolted between the electrode and the outgoing earthing conductor.
How often should I test through it?
At commissioning and then periodically (commonly yearly, or per your local electrical inspection requirement), and after any earthing fault.
What earth resistance is acceptable?
Commonly ≤5 Ω for general/equipment earthing and ≤10 Ω for lightning protection earthing — always check the standard that applies to your installation.
What is a test link made of?
Corrosion-resistant materials such as gunmetal, brass or hot-dip galvanised steel, so the joint stays low-resistance for years.
Ashlok manufactures earthing test links, chamber covers and the full range of earthing accessories in India since 1999. Explore earthing accessories → · New to earthing? Start with what is earthing.