CPI IQ generator: start-up faults from a damaged site earth
What happened
Generator errors 903, 904 and 905 at start-up. As reported in the case, the engineers measured a heavy phase imbalance on the incoming supply — about 260 V on one phase against 200–220 V on the other two — plus 15–30 V between neutral and protective earth.
What was checked
- Searched the service documentation and read the generator logs; the codes were not clearly explained there.
- Ruled out the operator side: confirmed no exposure button was held at power-up, per a remote suggestion.
- Measured phase voltages at the incoming supply and found a severe imbalance.
- Measured neutral-to-protective-earth voltage and found it far from zero, which pointed away from the generator itself.
Cause
The building's earthing circuit had been destroyed — the earth electrode loop outside was broken, reportedly by a snow-clearing vehicle. With the protective earth effectively lost, the supply drifted and the generator flagged mains faults. The codes were a symptom of a bad power and earthing condition, not a generator defect.
What was done
The earthing circuit was restored on site. The engineers also discussed with the site the quality of the incoming neutral and proper re-grounding of the neutral at the building. After the earthing work the generator ran without the reported faults.
Safety
A faulty protective earth is a direct shock hazard: frames and earthed parts can rise to line potential. De-energise the system before touching any earthing connections, and verify earth continuity plus an electrical safety test before the room returns to clinical use.
Lesson: When generator fault codes make no sense, measure the incoming supply and the neutral-to-earth voltage first — the generator is often just the messenger.
Covered in the course: X-ray Service — Level 2: Fault-Finding →
Written from an anonymised case shared by service engineers. It is not a manufacturer instruction and grants no authorisation. Independent note; names are trademarks of their owners.