A permit to work is a document issued by an authorised person stating exactly which equipment is safe, where it is isolated and earthed, what work may be done and which hazards remain. The person leading the work signs to accept it and keeps it until the job is complete, then it is cleared and cancelled before any isolation is removed. It sits at the end of a switching programme and is the core of high-voltage safety rules.
Isolations and earths are on, I'm issuing the permit to work for the CT change, sign here and keep it on you.
US utilities call the equivalent a clearance or hold order, so 'clearance' in a control room is about permission, not distance.
Also heard as
- PTW
- permit
- clearance
- hold order
Related terms
Switching order
Written step-by-step sequence of operations used to isolate or restore equipment safely.
Tag out
To hang a danger tag on an isolation point so nobody operates it while people work downstream.
Portable earths
Removable earthing leads clamped onto isolated conductors to short them together and to earth during work.
Prove dead
To test isolated equipment with a verified voltage detector and confirm no voltage before anyone touches it.