QUESTION 10.3.2

Electrical insulation monitoring and earth faults

Oil, Chemical, LPG, LNGEngine Control Room

What is being checked

The inspector is checking whether engineers understand insulation-monitoring settings, recognise earth faults promptly and prevent a first fault from remaining until a second fault causes shock, fire or equipment loss.

Ready onboard

0/6 complete

MONITORSPrimary and secondary insulated distribution systems have functional monitoring and alarm indications as required.SETTINGSAlarm settings are documented and appropriate to the system voltage, design and normal leakage.DAILY STATUSEarth readings and alarms are checked routinely and abnormal values are recorded.FAULT LOCATIONSafe fault-finding procedures, diagrams and suitable test equipment are available.DEFECT CONTROLKnown faults have identification, isolation where possible, risk assessment and repair priority.NO DEFEATAlarm muting, switched-off feeders or temporary bypasses are formally controlled and visible at handover.

Practice questions

Answer aloud, then open the preparation point.

1Why is the first earth fault serious on an insulated system?

It may not trip supply, but it removes the designed insulation margin and a second fault can create high current, fire, shock or loss of essential equipment.

2What is the normal reading and alarm setting?

State the actual values for this switchboard and explain the approved setting, not a generic resistance figure.

3How do you locate a fault safely?

Use drawings, load knowledge and an approved sectional isolation or test method while protecting essential services and personnel.

4Can an earth fault remain until port?

Only under formal risk control when immediate repair is unsafe or impossible; monitor it, protect redundancy and plan prompt rectification.

5Show the last earth-fault event.

Trace the alarm, affected feeder, investigation, isolation, repair and restored insulation reading.

Where an observation may arise

ACTIVE FAULT

A significant earth fault remains without investigation or control.

SETTING UNKNOWN

Engineers cannot explain the monitor range or alarm set point.

ALARM DEFECT

The monitor or remote alarm is inoperative, muted or bypassed.

UNSAFE SEARCH

Fault location relies on uncontrolled isolation of essential equipment or live work.

POOR RECORD

Readings or recurrent faults are not trended and handed over.

Master's practical note

Ask for the normal insulation value and the last deviation. A panel with no alarm may still be weak if the setting is inappropriate or the indication has never been function-tested.

Equipment boundary and references

Equipment boundary: Distribution arrangements vary between insulated and earthed systems. Apply the approved single-line diagram, class rules and maker instructions before interpreting values.

References

OCIMF SIRE 2.0 Question Library Part 2, Version 1.0, Question 10.3.2
SOLAS Chapter II-1 regulation 45
IEC 60092 series
Company electrical safety procedure

Last reviewed: 2026-09-10