5.1.1 Safe use of electrical equipment
SAFE USE OF ELECTRICAL EQUIPMENT
Introduction
What is electricity?
Electricity is all around us, and most of us use it everyday. But do you really know what electricity is?
To really understand electricity? You first have to start with an atom. Everything in the universe is made up of atoms. Let's look at this ant. We think of ants as being pretty small, but atoms are smaller, much, much smaller atoms are so small.
In fact, that one ant is made up of too many atoms to count more than a billion. If you take an object and keep breaking it down to smaller units, eventually, you'll be left with only atoms, which we can call the building blocks of everything. Atoms Have a couple of different parts. And a really important part of an atom is called an electron.
Not all atoms Have the same number of electrons. The number of electrons in an atom can change because electrons can move between atoms.
Electricity is the movement or flow of electrons from one atom to another. This flow of electrons is called current electric. Current electrons can move in all materials, but they can move through some materials better than others.
If electrons can move quickly and easily in a material, then that material is a conductor, anything that allows electric current to flow from one point to another.
The opposite of a conductor is an insulator. An insulator is a material that does not let electrons move Well and doesn't conduct electricity.
Have you ever seen the inside of a wire?
Inside is usually made up of copper or another conductive metal. While the outside is made of plastic, an insulator. The copper wire helps the electrons flow while the plastic insulator helps keep the electricity from being wasted and prevents us from being shocked to use electric current to power things.
You have to create a complete pathway for the electric current to follow. This is called an electric circuit.
An electric circuit is like a racetrack of Inductive materials that let the electrons flow in a specific way.
For example, let's try to light a light bulb. First, You need a power source like a battery next, you need to connect wires to the battery and finally, the light bulb press do, just like that the circuit has been completed, and the light bulb lights up.
Electric generators
Electric generators work on the principle of electromagnetic induction. A conductor coil or a copper coil, tightly Wound onto a Metal core is rotated rapidly between the poles of a horseshoe type magnet. When the coil rotates, it cuts the magnetic field, which lies between the two poles of the magnet. The magnetic field will interfere with the electrons in the conductor to induce a flow of electric current inside it. This is how electricity is generated.
The rotor shaft is attached with slip Rings. The stator surrounds the router and is attached to the three sets of copper wire coils or three phase windings. There are three sets because the generator is a three phase generator.
The arrangement can be of two or more than two electromagnets, more than a number of poles more the current produced.
Many ships are equipped with shaft generators where the rotations of the main engine of the ship is used to operate the alternator and generate additional electricity. .
Electricity is an essential part of modern life. People use electricity for lighting, heating, cooling, and refrigeration and for operating appliances like lights, fans fridges, computers, electronics, machinery, and public transportation systems.
A ship is like a floating city with all the privileges enjoyed by any normal land city. Just like a conventional city, the ship also requires all the cargo operations and basic amenities to sustain life on board; the chief among them is power or electricity. In this article we will learn as to how power is generated and supplied on board a ship.
Power generation On board
Shipboard power is generated using a prime mover and an alternator working together. For this an alternating current generator is used on board. The generator works on the principle that when a magnetic field around a conductor varies, a current is induced in the conductor.
The generator consists of a stationary set of conductors wound in coils on an iron core. This is known as the stator. A rotating magnet called the rotor turns inside this stator producing magnetic field. This field cuts across the conductor, generating an induced EMF or electro-magnetic force (Voltage) as the mechanical input (prime mover) causes the rotor to turn.
Power Distribution on board
All electric power consumed on board a ship is produced by onboard Generators.
Electric power is transmitted from the generator to electrical switch boards that distributed to a variety of installations and equipment on board The vessel.
Electrical switch boards are Dedicated to cableway, opening, closing, surveillance control and protection.
BUS BARS
Bus Bars which acts as a carrier and allow transfer of load from one point to another.
CIRCUIT BREAKER
Circuit breakers which act as a switch and in unsafe condition can be tripped to avoid breakdown and accidents.
FUSES
Fuses as safety device for machinery.
TRANSFORMER
Transformers to step up or step down the voltage. When supply is to be given to the lighting system and domestic utilities, a step down transformer is used in the distribution system. (Normally 440 v to 220 V or 110 V).
Power distribution
- In a power distribution system, the voltage at which the system works is usually 440v, 50/60 Hz , 3Ø.
- There are some large installations where the voltage is as high as 6600v.
- Power is supplied through circuit breakers to large auxiliary machinery at high voltage.
- For smaller supply fuse and miniature circuit breakers are used..
Earthed-Neutral
- The distribution system is three wires and can be neutrally insulated or earthed.
- Insulated system is more preferred as compare to earthed system because during an earth fault essential machinery such as steering gear can be lost.
Electrical Testing Equipment
Multi meter : Used to measure voltages in AC and DC, small current, continuity, resistance and etc.,
Clamp Meter: To measure high currents also have function to measure volts, continuity , resistance etc.,
Insulation tester (Megger): To measure the resistance value of Insulators of motor and cables.
When working with or testing any electronic equipment, it’s always important to be cautious. Whatever type of equipment you’re handling, whether simple or complex, it’s important to take the right safety precautions.
Working with electricity comes with huge risks that should never be taken lightly. If you’re a hobbyist who loves working with electronic components or an electronics professional at your workplace, safety should always come first.
To avoid personal injury, possible damage to equipment or danger of fire, work on electrical system should be conducted at well illuminated and ventilated place.
Before working on any electronics, consider following these basic safety precautions to help reduce any hazards.
• Remove any electronic equipment you’re testing or working on from the power source.
• Never assume the power circuit is off. Test and test again with a voltmeter to confirm.
• Remove fuses and replace them only after the power to the circuit is disconnected.
• Don’t connect power to a circuit until you’re done working on it and rechecked the work.
• Always ensure that all electronics equipment is properly grounded.
• If it’s damaged, replace it. For instance, replace cables instead of repairing with insulating tape.
• Always use the right electronics repair and maintenance tools.
• Always return covers after removing them to reduce the risk of electric shock.
• Make sure your circuit is not overloaded.
• Always have safety equipment like a fire extinguisher, a basic first aid kit and a mobile phone nearby.
Personal Safety
It’s important to ensure that you’re safe when working on electronic circuits. Here are some personal safety precautions to keep in mind:
• Always keep your work area dry.
• Always work in a well-ventilated area.
• Don’t wear flapping or loose clothing when working.
• Don’t work with metallic jewelry on your hands like watches, rings and bracelets.
• Don’t use bare hands to remove hot parts.
• Always wear non-conductive shoes.
• Always wear insulator gloves in your hands when carrying out repairs.
• When removing high-voltage charges on capacitors, always use a shorting stick.
• Don’t hold the test probs when measuring voltage over 300V.
• Always remove power to a circuit before connecting alligator clips.
• Always wear safety goggles.
• Be careful when handling large capacitors as they can still hold high voltage even after you’ve disconnected the circuit from power.
Isolation Procedures
Switching off the supply of electricity to allow for safe working is legally mandated, with work on or near to live electrical systems permitted in exceptional circumstances only. Electrical isolation consists of two clear stages: switching off the supply and proving dead. It is important you follow a safe isolation procedure.
Why do we need electrical isolation?
It is vital for safety. The consequences of failing to undertake electrical safe isolation can be dangerous and life-changing. Complacency and incompetence are often the underlying cause. HSE publication HSG85 Electricity at Work, Safe Working Practices is a good source of guidance on the requirements for working on systems made dead and for working on or near to live electrical systems.
Safe isolation procedure
Whilst the applications may differ, the 7 steps for safe isolation is similar for low voltage and for high voltage. The process goes as follows:
- identify suitable point(s) for isolation.
- carry out the safe isolation process.
- secure the point of isolation (place notices)
- prove dead
- apply safety earths
- place danger notices
- issue electrical permit to work
Different voltages on board
A ship is an independent floating structure having its own power plant for supplying electricity to its machinery and systems, which together assist in the propulsion of the ship from one port to another.
Shipboard power is generated when a prime mover and alternator works together. For this purpose, an alternating current generator is used on board. The generator works on the principle that as a magnetic field rotating around a conductor varies, a current is induced in the conductor.
AC, 3-phase power is preferred over DC as it gives more power for the same size .
In a power distribution system, the voltage which the ship’s system works is usually 440v.
Power on ships is supplied through circuit breakers to large auxiliary machinery at high voltage. For smaller supply fuse and miniature circuit breakers are used.
The power distribution system, consisting of three wires, can be neutrally insulated or earthed. Insulated system is more preferred as compare to earthed system, as during an earth fault essential machinery such as steering gear can be lost.
In case of failure of the ship’s main power generation system, an emergency power system or a standby system is used. The emergency power supply ensures that the essential machinery systems continue to operate the ship.
Batteries or an emergency generator or even both can supply emergency power on ships.
Ratings of the emergency power supply should be such that it is able to support all essential systems such as:
- Steering gear system
- Emergency bilge and fire pumps
- Watertight doors
- Fire fighting system
- Ship’s navigation lights and emergency lights
- Communication and alarm systems
Precautionary Measures while working on electrical systems and machinery
Nearly everyone has experienced an electric shock at some time. At best it is an unpleasant experience; at worst it is fatal.
Dangerous of Electric Shock
When Electricity passes through our body. We get an electric shock. Our body parts undergo a certain suffering. This is called an electric shock .
If any person receives a shock, the main switch off the power supply must be switched off. If the victim gets attached to the wire or the appliance do not touch him, but he must be Separated from electricity using a dry stick.
First Aid for Electric Shock
If you find that the victim has difficulty to take breath, give him artificial respiration CPR.
If restored breathing place him in recovery position at the open air else continue CPR till medical facilities arrive.
Effects of Electric Shock on Human body
How much electric current can the human body actually withstand?
There's a basic law and electricity called Ohm's law, which you will invariably come across while studying anything related to electricity.
The law defines the relationship between voltage and current flowing through a circuit.
To put this more simply, It says that the higher the number of amps, the greater the number of volts.
You may have seen warning messages on electrical boards and generators imprinted with the universally recognized emblem of danger, a human skull floating above to crossbones.
In addition to this symbol, There's also the rating of the machine in question, which typically highlights the voltage range at which it operates.
These Warnings tells that direct unprotected physical contact with a machine can be fatal, because these boards and many other warning signs consist of voltage ratings.
People tend to get the idea that a certain threshold of volts can be lethal for humans. People can get electrocuted by house appliances that operated only 110 or 230 volts.
In fact, there have been cases of electrocution by electrical apparatus that uses little as 42 volts of direct current.
This is why the real measure of a shock severity lies in the amount of current, or the number of amps being forced through the body, not the voltage. It is the number of amps being forced through their body.
Any amount of current over 10 milliamps is capable of producing severe shocks, but currents in the range of 100 to 200 milliamps could be very painful and even fatal.
Currents above 200 milliamps may produce severe burns and unconsciousness. But if immediate medical assistance is provided, the victim may still be saved.
If more than 200 milliamps pass through a person's body, The muscular contractions are so severe that the heart is forcibly clamped shut during the shock.
This is why providing immediate medical attention is the only way to improve the victims chances of survival as their heart may need to be restarted.
The volts, amps, frequency and duration of current that deals a lethal blow to the body .
If it were just the amps, then static electricity shocks like those you occasionally get when you touch doorknobs would be lethal, but they're not.
current can only be pushed through the body by volts, which can be lethal only when they're pushed at a certain frequency for a long enough duration.
The condition of the skin also plays a key role as a body's resistance to the flow of current may vary from 1000 Ohms for wet skin to over 500000 Ohms for dry skin.
In other words, It means that the severity of an electrical shock would be much higher if the skin is wet, because more current will flow due to a lower resistance.
Additionally, the actual resistance of the body also depends on the point of contact.
For instance, The internal resistance from hand to foot is nearly 500 Ohms, but only 100 Ohms between the ears.
Thus more current can flow between the ears, which makes that area more prone to injuries.
The risks of electric shock are much greater on board ship than they are normally ashore because wetness, high humidity and high temperature (including sweating) reduce the contact resistance of the body. In those conditions, severe and even fatal shocks may be caused at voltages as low as 60V. It should also be borne in mind that cuts and abrasions significantly reduce skin resistance.
A notice of instructions on the treatment of electric shock should be posted in everyplace containing electrical equipment and switchgear.
Precautions working on Electrical Systems and Machinery
Briefly discuss about the work procedure and safety precautions to be taken at all those involved.
Toolbox talks should cover every single aspect of the job. The pocket card should act as a checklist to help the person holding the talk, make sure he's covered everything. These talk should be held before, and, during the job and also, after it's finished.
First everyone needs to know why the job is being done, what it's for? The job plan methods to be used should be outlined and the nature of the workplace considered together with any specific hazards that might need mentioning.
You should also give your input. If you have any suggestions from other jobs or past experiences. These should all be highlighted and discussed. Throughout the talk, every possible risk should be assessed. Everyone should know, their individual roles and responsibilities.
If anyone is unsure about this, they should ask. In fact, everyone should contribute to the discussions at all times. Discussion of the work environment will include sea and weather conditions. Activities that may be taking place nearby which may conflict with the job and the safest methods of getting to and from the work site. The permit to work will give information about any necessary, personal protective equipment, tools materials, other equipment, and any isolations that are needed. The talk itself is an example of the sort of communications between everyone involved. That should be maintained at all times. It should stress that anyone with any questions or concerns should Express them at any stage.
Are you prepared?
Fill up electrical work permit by reading and understanding each and every line carefully by the person who is carrying out the job. Follow the procedure given in the work permit and (tick) select appropriate boxes.
- Before any work is done on electrical equipment, fuses should be removed or circuit breakers opened to ensure that all related circuits are dead.
- If possible, switches and circuit breakers should be locked open or alternatively, a 'not to be closed' notice attached.
- Where a fuse has been removed, the person working on the equipment until the job is finished should retain it. A check should be made that any interlocks or other safety devices are operative.
- Additional precautions are necessary' to ensure safety when work is to be undertaken on high voltage equipment (designed to operate at a nominal system voltage in excess of I kV). The work should be carried out by, or under the direct supervision of, a competent person with sufficient technical knowledge and a permit-to-work should be operated.
- Some parts of certain types of equipment may remain live even when the equipment is switched off. Power should always be cut off at the mains.
- Flammable materials should never be left or stored near switchboards.
- Work on or near live equipment should be avoided if possible but when it is essential for the safety Of the ship or for testing purposes, the following precautions should be taken.
- Before attempting any electrical work, there are some basic safety precautions you must bear mind. The possible dangers arising from the misuse of electrical equipment are well known.
- Electric shock and fire can cause loss of life and damage to equipment.
- Before working on the drive of any machine, isolate it from its power supply in a way that prevents the machine from being accidentally started.
- Regulations exist to control the construction, installation, operation and maintenance ofelectrical equipment so that danger is eliminated as far as possible. Minimum acceptable standards of safety are issued by various bodies including national governments, international governmental conventions (e.g. SOLAS), national and international standards associations (e.g. BSS and IEC). learned societies (e.g. IEE), classification societies (e.g. Lloyds), etc. Where danger arises it is usually due to neglect or contravention of the regulations,
You must learn to operate equipment in a safe manner and maintain it in a safe condition at all times. Failure to do so will not only endanger your life but life of others too. Keep in mind
An essential list of Dos and Don'ts when working with electrical equipment.
Dos
- DO get to know the ship's electrical system and equipment. Study ships' diagrams to pinpoint the location of switches and protection devices supplying distribution boards and essential items of equipment. Write down this information in a notebook. Note the normal indications on switchboard instruments so that abnormal operation can be quickly detected.
- DO operate equipment according to manufacturers' recommendations.
- DO maintain equipment according to manufacturers' recommendations or ship maintenance procedures.
- DO ensure that all guards, covers and doors are securely fitted and that all bolts and fixings are fitted and tight.
- DO inform the Offcer of the Watch before shutting down equipment for maintenance.
- DO switch off and lock off supplies, remove fuses, and display warning notice before removing
covers of equipment for maintenance.
g) DO confirm that circuits are DEAD (by using a voltage tester) before touching conductors and terminals
Don'ts
- DON'T touch live conductors under any pretext.
- DON'T touch rotating parts,
- DON'T leave live conductors or rotating parts exposed.
- DON'T stand on unstable platform when working at height.
- You should think 'safety' at all times. Develop a safety conscious attitude. This may well save your life and the lives of others. Most accidents occur due to a momentary loss of concentration or attempts to take short cuts to safety procedures. DO NOT let this happen TO YOU .
