Safe Isolation of Supplies

In all but the most rural areas, consumers can connect to a metallic earth return conductor, which is ultimately connected to the earthed neutral of the supply. This, of course, presents a low-resistance path for fault currents to operate the protection.

In summary, connecting metalwork to earth places that metal at or near zero potential and bonding between metallic parts puts such parts at a similar potential even under fault conditions. Add to this a low-resistance earth fault return path, which will enable the circuit protection to operate very fast, and we have significantly reduced the risk of electric shock.

We can see from this how important it is to check that equipment earthing is satisfactory and that there is no damage to conductor insulation.

SAFE ISOLATION OF SUPPLIES

Before any work is undertaken on low-voltage (50–1000 V AC) installations, supplies should be isolated and proved dead; the procedure is as follows:

1. Identify the circuit or item to be worked on. 2. Switch off/isolate and lock off or place warning notices if locking is not available. 3. Select a suitable approved voltage indicator and check that it works, on a known supply. 4. Test that the circuit or equipment is dead using the tester. 5. Recheck the tester on the known supply again.

Never assume or take someone else’s word that supplies are dead and safe to work on. Always check for yourself.

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