TT Earthing
Installation earthed via its own electrode.
● Line● Neutral● Earth
Tap any wire, switch or device to see what it is.
Useful Information
No DNO earth. The installation relies on its own electrode and RCDs for fault protection.
Important to know
- RA × IΔn ≤ 50 V (411.5.3).
- RCDs required for fault protection.
- Electrode resistance above 200 Ω may not be stable (GN3).
Testing tips
- Measure RA with an earth loop tester or electrode tester, with main earthing disconnected (safely).
BS 7671:2018+A4:2026 references
411.5.3542.2543.1
Study notes paraphrased — check against your copy of BS 7671.