Testing & Teaching
Proving Unit
In short
A proving unit is a small box that gives a known test voltage. Its terminals: P1, P2.
If this is your home: this page is written for heating engineers. Mains wiring and gas appliances are not DIY jobs; call a Gas Safe registered engineer. If you smell gas, leave the building and call the National Gas Emergency Service on 0800 111 999.
What it is
A PROVING UNIT is a small box that gives a known test voltage. Put both of the two-pole tester's probes on its sockets: the tester lights, and is PROVED to work.
GS38, the Health and Safety Executive's (HSE's) guide to electrical test equipment, says: prove the tester before the dead test, make the test, then prove it again.
It gives nothing to the circuit: it is only for proving a tester.
Terminals
| Terminal | What it is for |
|---|---|
| P1 (Prove +) | One socket, for one probe. |
| P2 (Prove -) | The other socket, for the other probe. |
What the meter reads
Both probes on it: every light (LED) on the tester comes on, and so does its PROVED lamp.
Where it connects
Lessons that use it
- Why we work dead
Foundation · Safe isolation and the earth
- Prove dead
Foundation · Safe isolation and the earth
- The swap method
Intermediate · Swapping controls
- Safe isolation: prove dead before you start
Quick Jobs
Also in testing & teaching
Read the explanation
- Safe isolation in five steps: prove, confirm live, isolate, test every pair, prove again
Heating wiring is done dead. Prove the tester, confirm the supply is live, isolate and lock off, test every pair, prove the tester again. Why each step matters.
Practise it in the simulator.
Runs in the browser on a laptop or desktop. Cancel any time.