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28/05/2024

Low insulation 220V. First actions of the ETO

Greetings! In this article we will analyze the first actions of the ETO when low 220V insulation occurs on a ship. How to find the source of low insulation and what steps to do in such situation.

Low insulation 220V
Low insulation 220V

On a vessel it is very important to pay special attention to this, because by promptly eliminating low insulation, you can prevent dangerous smoke or even fire.

As often happens, the “Low insulation 220V” alarm goes out to the alarm monitoring system in the ECR and the ETO has to look for the source of low insulation on the ship.

Alarm on monitoring system
Alarm on monitoring system

The way to find low insulation is to turn off the circuit breakers on the 220V feeder panel of the main switchboard one by one and at the same time monitor the megohmmeter needle. 

Feeder panel 220V on the main switchboard
Feeder panel 220V on the main switchboard

The megohmmeter shows how the insulation resistance of the ship's electrical network changes in real time, so if you turn off the desired circuit breaker (de-energize a group of consumers with low insulation), its needle should instantly point towards infinity.

Ground monitor
Ground monitor

The alarm setting for the ground monitor is 0.01 MOhm. What should the value be? I'm waiting for your answer in the comments.

The first action of an electrician when searching for low insulation is to turn off the desired circuit breaker and narrow the search. Non-essential consumers are turned off first, these could be outlets or lights on the deck, galley, washing machines and dryers.

Indication of low insulation on the main switchboard
Indication of low insulation on the main switchboard

  1. The first circuit breaker that I turn off is the lighting and sockets for the forecastle. 
  2. The second circuit breaker is the galley and laundry. 
  3. The third breaker is for lighting and power outlets on the main deck and aft part. 
  4. Next, I turn off the navigation lights, lighting and engine room outlets section by section.
  5. If none of the above helps, then you have to turn off the cabins. At the same time, it is necessary to make an announcement so that the crew turn off their computers and phones from the sockets.
  6. If this is not the problem, then you need to turn off systems and devices that use 220V. For example, fire alarm system, water ingress alarm system, public address system, shaft power meter, etc.

If all the circuit breakers are turned off, but the insulation is still low, then you need to inspect the main service transformer, but it rarely comes to that.

After the main circuit breaker has been found, it is necessary to take a portable megger and inspect the secant circuit breakers of this group. Each phase must be measured relative to the ground (hull) (be sure to remove power from the phase).

Portable megger (megaohmmeter)
Portable megger (megaohmmeter)

Next we go to the source of low insulation directly. Below are the most common problems with low insulation on a ship.

Rusty light fixtures collapsed

Rusty light fixtures collapsed

Rusty light fixtures collapsed

Rusty light fixtures collapsed
Rusty light fixtures collapsed
Anchor lights flooded by a wave
Anchor lights flooded by a wave
The heating elements burned out in the washing machine
The heating elements burned out in the washing machine
Floodlight terminal box flooded
Floodlight terminal box flooded
The ballast in the outdoor lamp burned out
The ballast in the outdoor lamp burned out

All of the above cases of poor insulation on a ship are only a small part of the reasons why the low insulation 220V alarm occurs. An electrical engineer's job is to find and fix these problems.

Let's consider a real situation when low insulation 220V came out. When switching off the circuit breakers, the breaker of the 4th group with low insulation was found.

Breaker of the 4th group
Breaker of the 4th group

Using a portable megger, we found the 9th circuit breaker in the 4th distribution board with low insulation.

Checking the insulation resistance of the 9th circuit breaker

Checking the insulation resistance of the 9th circuit breaker
Checking the insulation resistance of the 9th circuit breaker. 9th circuit breaker with low insulation

From the diagram we see that this circuit breaker has many different sockets.

Consumer diagram of the 9th circuit breaker
Consumer diagram of the 9th circuit breaker

As a result of testing all sockets one by one, an socket with low insulation was found in the SUEZ CREW room.

Socket with low insulation

Socket with low insulation
Socket with low insulation

Despite the fact that this was a room, the outlet was located practically on the open deck (with access to the starboard side of the main deck) and experienced maximum loads from the aggressive marine environment. After replacing the socket, the 220V insulation was restored to normal.

It is very important to know the operating conditions of the vessel and understand what is currently turned on and what could lead to low insulation. 

For example, the ship is in maneuveringmode and is passing through a narrow channel; the Steering Light on the bow mast is turned on. The ship is passing through the Suez Canal and has turned on the Suez lights or anti-fog projector light on the forecastle. The ship approaches Singapore and the special three green lights on the masthead are turned on. This may result in poor insulation of these lights. All these and other examples indicate that something is always turned on and off on a ship, and it is important to understand what exactly and when.

To check such lights or outdoor lighting, you need to check the phases on the contactors that are activated when the lights are turned on.

Typically, the activation of exterior lighting, navigation and special lights occurs on the bridge.

Navigation light panel
Navigation light panel
Outdoor lighting panel
Outdoor lighting panel

For example, we pressed the "ACC. OUTSIDE PASSAGE LIGHT (UPPER DECK)" button, the MC2 contactor in the distribution panel of the 4th group of breakers was activated and the external lighting on the main deck turned on.

Check 1408 and 1406 to the ground
Check 1408 and 1406 to the ground

So in this case we must check the circuit to the ground after the contactor. 

Contactor MC2 in the circuit diagram
Contactor MC2 in the circuit diagram

If we measure the phase resistance to the ground after the breaker, then only the circuit “contactor - breaker” will be checked.

Earth Test
Earth Test

Finally, we’ll do an Earth Test to make sure that the megohmmeter is working properly and that none of the phases are “sitting” on the ground.

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