Polarity testing (dead and live)
Polarity proves every single-pole device — switches, fuses, circuit breakers — is in the line conductor, and that sockets and lampholders are connected the right way round.
Why it matters
If a switch is in the neutral, the light goes off but the lampholder is still live. If a socket is reversed, appliance fuses and switches end up in the neutral. Both are hidden dangers that only testing finds.
Dead polarity (with the R1+R2 link)
- Link line to cpc at the boardThe same link used for the R1+R2 test.
- Test at every pointAt each socket, switch and lampholder, a low reading between the line terminal and earth proves the line conductor is where it should be.
- Operate switchesCheck the switched line goes through the switch — the reading should change when the switch is operated.
- ES lampholdersThe centre contact must be connected to the line conductor.
Live polarity at the origin
Once the supply is connected, confirm the incoming supply polarity with an approved voltage indicator before energising circuits:
| Between | Expected (single-phase) |
|---|---|
| Line – Neutral | about 230 V |
| Line – Earth | about 230 V |
| Neutral – Earth | about 0 V |
An earth fault loop tester will also usually warn of reversed polarity.
iZapp’s 3D Testing Bench lets you do this test on a virtual board with real-looking kit: place the probes, read the tester and record the result on a practice schedule. Some attempts have a fault planted for you to find.
Frequently asked questions
Is polarity a live or dead test?
Both. Most polarity checks are done dead using the R1+R2 link; supply polarity is confirmed live at the origin.
Which way round is an ES lampholder connected?
The centre contact goes to the line conductor, so the screw shell (which can be touched) is neutral.
Last updated 2026-10-14. Training summary of BS 7671 and IET Guidance Note 3 practice, written by NAPIT-registered electricians. Always check the current edition and amendment of BS 7671 and your scheme’s requirements.