How To Detect Ground Faults On Board Ship?

How To Detect Ground Faults On Board Ship?

Ground faults are extremely dangerous on board. Some ships operating on 440 volts do not even have individual fault circuit breakers. However, when the operating voltage exceeds 3,000 volts, a protection system that isolates the machinery in the event of a ground fault is mandatory.

When a ground fault occurs, the severity of the action to be taken depends on the part of the electrical system affected. Conventional ships operating on a three-phase 440-volt system have ground fault indicators installed on all three phases. Any ground fault in a 440-volt system is considered a serious problem and requires immediate action to identify the faulty circuit.

A ground fault in a 220-volt or low-voltage lighting circuit may be considered a serious problem, but does not require immediate action. However, it should be addressed as soon as possible.

Detecting Ground Faults in 440-volt Circuits

When a ground fault alarm is triggered, immediately notify the ship's electrician (if any). The first step is to verify the alarm's validity. Usually, there is a test button on the board to reset the alarm and check the ground fault status.

If the vessel is equipped with an Integrated Automation System (IAS), check the computer for a list of events that triggered the alarm. If there is no IAS, there is only one option: isolate all machinery on the 440-volt circuit and check whether the ground fault indicator returns to normal.

Not all machinery running on a 440-volt circuit can be isolated. Some important equipment, such as steering gear and lubrication oil pumps, cannot be isolated during navigation. However, a ground fault can be detected by switching from operating machinery to standby machinery.

Detecting ground faults on 220-volt circuits is more difficult than detecting ground faults on 440-volt circuits. The main reason is the lighting circuits around the vessel. However, any ground fault alarm in a 220-volt circuit is usually important but not an emergency.

As mentioned earlier, when a 220-volt ground fault alarm is triggered, pressing the test button verifies its accuracy and then starts a test on each 220-volt circuit.

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Example: A 220-volt switchboard triggers a ground fault alarm.

• Check the accuracy of the alarm.
• Isolate the entire group, start the panel of the lighting section one by one.
• Check the status of the ground fault indicator (is it still faulty or working properly).
• If a fault occurs, reconnect the previously disconnected circuit breaker and isolate the other group start panel of the lighting circuit. After identifying the group start panel, turn off the lighting circuit breakers one at a time and check the alarm status.

When the situation returns to normal after the circuit breaker is turned off, the lighting circuit can be identified and tested for any faults in that lighting circuit. Moisture intrusion is the most common cause of ground faults.

Alternative way:

Instead of turning off the lighting circuit breakers one by one, I took a method of turning off the entire lighting circuit in a specific area. This method is often useful when two or more faults occur in the 220-volt lighting circuit. Turning off all the circuit breakers in a zone and then turning them on one by one can avoid multiple ground faults.

It is challenging to identify multiple ground faults by turning off the lighting circuit breakers one at a time.

After identifying the faulty circuit, we need to separate it into its parts and check for a ground fault. To do this, we use a megohmmeter for grounding as usual.

By disconnecting the fuses on both phase lines, each line can be tested, and the fault can be identified.

Why does an earth fault alarm instead of tripping the breaker?

The 440-volt distribution on most merchant ships is run unearthed, with no deliberate connection between the system and the hull. A single fault to earth therefore completes no circuit, and the supply keeps running. That is a design choice: steering gear, lubricating oil pumps and the emergency switchboard cannot be dropped because one cable core has gone down to the structure.

The danger is the second fault. An earth fault on another phase turns two separate insulation failures into a phase-to-phase short circuit through the hull, limited only by cable impedance. Breakers trip, and the blackout arrives at whatever moment that second fault happens to occur. That is why a 440-volt indication is chased down at once while a lighting circuit can usually wait.

SOLAS Chapter II-1, Regulation 45 is the requirement behind the indicator lamps. It obliges a distribution system with no connection to earth to carry a device that continuously monitors the insulation level and gives an audible or visual indication when it falls. Class surveyors and port state control inspectors test that alarm, so a dead lamp or a disabled buzzer is itself a deficiency.

What to disconnect before the megger goes on

Insulation testing on these circuits is normally done at 500 volts DC, with the breaker racked out and the circuit proved dead. Anything carrying electronics comes off first: variable frequency drives, PLC input cards, alarm and monitoring boards, and any surge suppression fitted at the terminals. The test voltage destroys them, and the result is a burnt module on top of the original fault.

Readings move with temperature and moisture, so compare like with like. A motor megged cold after a weekend in a damp compartment reads lower than the same motor an hour after running. Space heaters left switched off, a leaking gland, deck washing above a junction box and condensation in an unused starter panel account for a large share of shipboard earth faults.

Record what each circuit reads rather than only whether it passed. Values drifting down over several months point to a winding that will fail in service, which is a spares decision rather than an emergency. A circuit that recovers once the heaters have run for a few hours points to moisture, and drying it out is cheaper than a rewind.

The same isolation rules cover any live work, set out in minimizing the risk of electrical shock on board.