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Safe isolation on a periodic, with the open-PEN checksWhy clamp the earthing conductor before you switch off?
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On a TN-C-S supply the PEN conductor can come loose from the star point. The circuits stop working, but they’re still live — and everything bonded to the MET can sit at a dangerous voltage: the board case, the pipes, the sink. So the isolation below checks for it before you trust anything is dead.
- Turn the loads off first, then the main switch. It’s rated to switch on load, but there’s no need to make it — and later you can bring circuits back one at a time.
- Ask before you switch anything off. It’s someone’s home.
Guidance Note 3 · Section 3 · safety in inspection and testing Guidance Note 3 · Appendix D · neutral current diversion
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- 18th Edition
- Building Regs
- PAT
- Fundamental Inspection & Testing
- Initial Verification
- Periodic Inspection & Testing