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ADS, and not assuming the earthing arrangementNo earthing conductor. Is it TT?
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Guidance Note 3 · p.34. Automatic disconnection of supply is fault protection — which is a different thing from basic protection.
| Provided by | |
|---|---|
| Basic protection | Basic insulation, barriers and enclosures |
| Fault protection — ADS | An earthing arrangement, protective devices, bonding conductors, correctly sized conductors |
The designer chooses the earthing arrangement, and the DNO confirms it
✋Never decide the earthing system from a glance. It needs to be confirmed, in writing, on paperwork.
The trap
You look at the service head. There is no earthing conductor. The obvious conclusion is: it must be TT. But it might be TN-C-S with the earthing conductor missing — never installed, or left out by the installer or the DNO.
What you actually do. Go outside and look for the earth electrode cover. If there is no electrode, enquire with the DNO. If they confirm TN-S or TN-C-S, then there is an earthing conductor missing that has to be installed straight away — and they will give you access to the service head to do it.
Designing for the environment. Horse stables twenty miles from the nearest town is a TT system, and everyone knows it. The earthing arrangement follows what is around you.
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- Building Regs
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- Fundamental Inspection & Testing
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