Work Permit Systems, Working at Height and Emergency Procedures
This domain tests the formal safety system for distribution work: permit-to-work, isolation, locking and tagging, proving dead, earthing, working at height and emergency response. The exam expects the correct sequence, not just a list of safety items.
Core rules
- A permit-to-work is issued by an authorised person after the equipment is isolated and made safe. The recipient must understand the limits of the permit and must not work outside them.
- Line-clear procedure: open the breaker, open the isolator, rack out or lock the isolating device, apply danger tags and locks, test for voltage at the work site, then apply earths on all sides of the work. Prove dead with a tested voltage detector.
- Earthing must be applied at the work site, not only at the substation. Earths must be rated for fault current and connected in the correct order.
- Work at height requires a suitable ladder or platform, a safety belt or harness anchored correctly, a helmet, and a rescue plan. Keep three points of contact on a ladder; set the ladder at about 75°.
- On electric shock, isolate the supply before touching the casualty, call for help, start CPR if trained and the casualty is not breathing, and arrange urgent medical aid.
Worked example
An 11 kV feeder is to be worked on. The correct sequence is: obtain and sign the permit; open the feeder breaker; open and lock the isolator; apply danger tags; test the conductor at the work site with a proved voltage detector; apply earths on both sides of the work; carry out the work; remove tools and earths; cancel the permit; then restore supply. If the tester is not proved before and after use, the “dead” result is not trustworthy.
Traps that cost marks
- Trusting a switch position instead of testing and earthing.
- Earthing only at the substation and not at the work site.
- Removing another person's lock or tag.
- Working at height without a rescue plan.
- Touching a shock victim before isolating the supply.