Portable earths are heavy flexible copper leads with clamps, applied with an insulated stick to every phase of an isolated line or busbar after proving dead and connected to an earth point. If the circuit is wrongly re-energised, induced by a parallel line or struck by lightning, the earths carry the current and hold the work site near earth potential until protection trips. They are rated for the fault level and inspected regularly, because a burnt clamp gives false security.
Portable earths on at both ends and one at the work position, put all three on the permit before you hand it over.
North American crews call the same kit grounds and talk about hanging grounds rather than applying earths.
Also heard as
- grounds
- protective grounds
- temporary grounds
- earthing leads
Related terms
Permit to work
Formal written authority to work on equipment that has been isolated, earthed and declared safe.
Prove dead
To test isolated equipment with a verified voltage detector and confirm no voltage before anyone touches it.
Hot stick
Insulated fibreglass pole used to operate, test or earth high-voltage equipment from a safe distance.