Separated CPC — AC isolator to inverter
On the same property as Find 001. The earth conductor between the AC isolator and the inverter had come apart. On a live generating system, that’s not a potential danger — it’s danger present.
The find
The photo from the isolator box (below) shows the wiring arrangement. Brown and blue conductors for live and neutral, yellow-green for earth. The CPC — circuit protective conductor — between the isolator and the inverter had separated at the termination point. Not missing entirely. Not cut. Separated: it had been connected at some point, and it wasn’t anymore.
[Photo: AC isolator box showing wiring — upload as blog/what-i-found/images/002-isolator-cpc.jpg]
What you’re looking at
The CPC is the earth conductor — the yellow-green wire that runs alongside the live and neutral in every circuit. Its job is to provide a low-resistance path to earth so that if a fault develops (a live conductor touching metalwork, for example), the fault current has somewhere safe to go. That safe path causes the protective device to trip immediately.
Between the AC isolator and the inverter on this installation, that path was broken. The inverter generates electricity. If a fault developed inside the inverter — or between the inverter and the isolator — the fault current had nowhere to go. The RCBO would not trip. The metalwork of the inverter could become live.
Why it matters — the analogy
The earth path is like an emergency fire exit. You might never need it. But if you do, it has to be there, unobstructed, and it has to work. A separated CPC is a fire exit with a locked door. The exit exists on paper — you can see it — but under the conditions that matter most, it won’t open.
Continuous vs broken CPC — what changes
The fault code
C1 — Danger Present. The system was generating at the time of inspection. With no continuous CPC between the isolator and the inverter, the metalwork of the inverter has no safe earth path. If a fault develops in that section, fault current cannot flow to earth, the protective device cannot operate, and any metalwork in contact with the fault becomes live. That is not a potential risk — it is an existing danger. Immediate remedial action required.
The fix
Re-terminate the CPC at the point of separation, ensure the termination is secure and correctly torqued, and verify continuity of the earth path from the isolator through to the inverter. A continuity test with a calibrated multifunction tester confirms the repair. Straightforward work — provided someone is looking for it in the first place.
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The MCS certificate confirms the system was registered. An EICR confirms the electrical connection is safe.
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