Testing & Teaching
Two-Pole Tester (voltage indicator)
In short
A two-pole tester, a voltage indicator, is the instrument safe isolation is done with. It has two probes and a ladder of lights (LEDs).
If this is your home: this page is written for heating engineers, and for learners under the supervision of one. It explains how the wiring works; it is not training to do the work. In England and Wales, electrical work in a home must meet the Building Regulations (Part P), and some of it must be notified to building control or done by a registered electrician; Scotland and Northern Ireland have their own rules. For the wiring, call a registered electrician or a heating engineer competent in controls. Work inside a gas boiler is for a Gas Safe registered engineer only. If you smell gas, leave the building and call the gas emergency number: 0800 111 999 in Great Britain, 0800 002 001 in Northern Ireland.
What it is
A TWO-POLE TESTER, a voltage indicator, is the instrument SAFE ISOLATION is done with. It has two probes and a ladder of lights (LEDs). It has no ranges to set, and it does not read resistance.
The method:
- Prove it on the proving unit.
- Test every conductor against every other.
- Read dead on all of them.
- Prove it again.
A reading on a live circuit proves it too.
What the meter reads
Live tests. On site, any reading taken with the supply on is work on or near live parts. Regulation 14 of the Electricity at Work Regulations 1989 allows it only when working dead is unreasonable, as when a fault shows only while the controls work, and only with suitable precautions: test leads made to the HSE’s guidance note GS38, fingers behind the guards. Regulation 16 allows it only for a competent person, or a learner under the supervision of one. Wiring and repairs are always done dead. In the simulator, nothing is live.
230 volts (230 V): every light (LED) is lit. Dead: none.
DC as well, either way round: direct current (DC), as on an OpenTherm pair. With nothing on the pair, about 24 V DC, it lights the 12 and 24 V LEDs.
The PROVED lamp means the TESTER works, never that the circuit is dead. It is this simulator's own: a tester on site simply lights on a known live.
It lights on the proving unit, or on a live circuit of 50 V or more. It goes out on a dead reading. So after the dead test, prove the tester again.
Where it connects
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.