what is Insulators? Definition, Properties, Types, Materials & Applications

Insulators

Dielectric insulators are materials that do not let electric current pass through them easily. This is because they have almost no free electrons inside them. You can think of them like strong walls that stop electricity from going through.

Under normal conditions—like regular voltage and temperature—these materials stay safe and do not conduct electricity. They are mostly non-metallic. Each of them can handle a certain amount of voltage before breaking down. This limit is called dielectric strength, and we measure it in kilovolts per millimeter (kV/mm).

Some common examples of dielectric insulators are:

• Mica
• Glass
• Asbestos
• Bakelite
• PVC (Plastic)

These materials are used in many electrical devices to keep us safe and to stop electricity from flowing in the wrong places.

Properties of a Good Insulator

A good dielectric insulator should have:

High Strength to Stop Electricity:
The material should be very strong so that electricity cannot pass through it easily. This is important for machines that work at high voltage.

Very High Resistance:
The material should not let electricity flow through it at all. Its resistance should be more than 10 ohm-centimeters. This keeps everything safe.

Can Handle Heat:
While working, machines can get hot. The insulating material should be able to release this heat so that it doesn’t stop working or get damaged.

Easy to Find and Not Expensive:
The material should be low-cost and easily available, so it can be used in many everyday electrical items.

Strong and Long-Lasting:
It should be tough and not break easily, even when used for a long time.

Not Affected by Water or Moisture:
Even during rainy or humid days, the material should keep working well and not lose its insulating power.

Easy to Shape:
The material should be flexible enough to be made into different shapes. This helps in building different types of electrical tools and devices.

Working of Insulators

To understand how an insulator works, let’s imagine how electricity moves inside different materials.

Every material is made up of tiny particles called atoms. And inside these atoms, there are even smaller particles called electrons. These electrons are the ones that help electricity move from one place to another.

Now, think of the electrons sitting in two zones:

• Valence Band – This is where the electrons normally stay.
• Conduction Band – This is where electrons need to go if they want to help electricity flow.

Between these two zones, there’s a space called the energy gap. You can imagine it like a big wall or a river that the electrons must jump over to reach the conduction band.

What Makes an Insulator Special?

In materials like wood, rubber, or plastic, this energy gap is very wide. The electrons don’t have enough energy to cross this big gap. Since they can’t make the jump, they stay stuck in the valence band. And if they don’t reach the conduction band, electricity cannot flow.

So, no matter how much you try to pass current through an insulator, it simply blocks it. That’s why these materials are used to cover wires or make handles for electrical tools—to keep us safe from electric shocks.

Compared to Conductors

In conductors like copper or aluminum, this energy gap is tiny or almost not there at all. So electrons can easily move from the valence band to the conduction band. This smooth movement allows electricity to flow easily through them.

Classification of Insulators

Insulators are materials that do not allow electricity to pass through them. They help to protect us from electric shocks and are used in many electrical appliances and machines. Insulators are mainly divided into three types:

1. Solid Insulators

These insulators are hard and have a fixed shape and size. You can hold them in your hand. They do not change their form. Some common solid insulators are:

• Ebonite
• Mica
• Bakelite
• Porcelain
• Glass
• Marble
• Slate
• Dry wood
• Fibre

These materials are strong and are used in switches, wires, and other electrical parts to keep electricity safely inside.

2. Liquid Insulators

These are materials that can flow like water. They do not have a fixed shape and take the shape of the container they are kept in. One good example is mineral oil, which is used inside transformers to keep them cool and safe.

Some soft and bendable insulators like PVC, micanite, and resin also come under this group, even though they are not liquids, because they are flexible and used in similar ways.

3. Gaseous Insulators

These insulators are gases that fill the space around us but cannot be seen. They also stop electricity from passing through. Some common gaseous insulators are:

• Dry air
• Nitrogen
• Hydrogen

These gases are often used in special equipment to prevent sparks and keep things safe.

Semiconductor

A semiconductor is a special type of material. It behaves like a conductor sometimes and like a non-conductor (insulator) at other times. That means it can allow electricity to pass through it in some situations, and stop it in others.

Examples of semiconductors are germanium, silicon, selenium, and carbon. If we look at their atoms, each has four electrons in its outer orbit.

When these materials are pure and kept at a very low temperature, they act like non-conductors. But when we add a small amount of impurity, or shine light or heat on them, they start working like conductors and allow electricity to pass through. This is what makes semiconductors very useful.

Properties of Good Semiconductors

Here are some important properties that make semiconductors special:

Their resistance decreases when they get hot

In normal wires (conductors), when we increase the temperature, their resistance becomes higher — which means electricity finds it harder to flow. But in semiconductors, the opposite happens. As the temperature goes up, their resistance becomes lower, and electricity flows more easily.
This happens because heating gives energy to the electrons, which helps them move freely.

We can control their conductivity

Just by adding a tiny amount of another material (called an impurity), we can greatly increase how well a semiconductor conducts electricity. This is something we cannot easily do with normal conductors like copper or aluminum.

Different type of atomic bonding

The way the atoms in a semiconductor hold each other is different from the way atoms in a conductor hold together. This bonding plays a big role in how semiconductors behave.

Semiconductors are very important in the world of electronics. They are used in computers, mobile phones, lights, and many smart devices because of their special ability to control electricity.

In simple words, they are like smart gates — opening and closing paths for electricity when needed.

In Simple Words:
Solid insulators are hard like glass or wood.
Liquid insulators can flow like oil.
Gaseous insulators are invisible like air.

Types of Insulators

Electricity always tries to find a path to the ground. If it flows in the wrong direction, it can be dangerous. That’s why we use insulators — special things that stop electricity from going where it shouldn’t.

Insulators hold up the electric wires on poles and keep the electricity from escaping. They are very important for keeping power lines safe and working properly.

Insulators are made from materials that do not let electricity pass through them. Some simple materials like rubber, wood, plastic, or mica can stop electricity. But in power systems, we use stronger and more reliable materials like glass, ceramic, porcelain, steatite, and polymers.

Porcelain and glass are used often because they are strong and don’t let electricity pass, even in bad weather.
Steatite is a special material. It works well at high temperatures, has good strength, and doesn’t lose much energy. That makes it great for keeping wires safe in electrical systems.

Now let’s look at the five main types of insulators used in electrical work:

1. Suspension Insulator

A suspension insulator looks like a string made of round plates. These plates are called disc insulators, and they hang one below the other. The electric wire is attached to the bottom disc.

These insulators are used for high voltages – more than 33,000 volts. If more voltage is needed, more discs are added to the string. Each disc can handle about 11,000 to 15,000 volts.

Because the wire hangs below the pole using this type of insulator, the height stays within the limit of the pole. This setup also protects the wires better during lightning.

2. Pin Insulator

Pin insulators are one of the oldest types. They sit directly on the pole and hold the wire in place. They are strong and simple in design.

Pin insulators are used for medium voltages, between 11,000 and 33,000 volts. They are easy to install and need very little care. These insulators can be placed straight up (vertical) or sideways (horizontal).

3. Strain Insulator

A strain insulator is used when the electric wire is pulled tight, like at the end of a line or when the line turns sharply. These places need something strong to hold the tension in the wire.

That’s where strain insulators help. They not only stop electricity from passing through but also carry the heavy pull of the wire. They are very strong and are often used where wires face a lot of pressure.

4. Stay Insulator

A stay insulator helps support the poles that carry the electric wires. It is fixed to the stay wire or guy wire—this is a wire that pulls and holds the pole straight, especially at the ends.

Stay insulators stop the electric current from reaching the ground through these wires. They are usually made of porcelain and are shaped like an egg. This keeps things safe around low-voltage wires.

5. Shackle Insulator

Shackle insulators are also called spool insulators. These are mostly used in low-voltage areas. You can fix them straight up or sideways, depending on where they are needed.

They have a small hole in the middle that spreads the pressure evenly. This helps avoid breaking. The wire is tied into the groove of the shackle using a soft binding wire. These were used more before, but now they are less common because many wires are placed underground.

Post Insulator

A post insulator is a strong and reliable support used in electrical systems, especially in places like substations or inside buildings. It stands upright and holds the electric wire or conductor at the top. This type of insulator doesn’t just keep the electricity flowing safely — it also keeps everything steady and in place.
It is made to handle both the weight and the electrical power, without breaking or letting the current leak. That’s why it’s trusted in places where safety and strength really matter.

Disc Insulator

A disc insulator is mostly used in areas where high-voltage electricity flows — like long-distance transmission lines.
It looks like a chain of small round plates, usually made of glass or porcelain, joined together by metal links. These discs hang like a string and support the heavy wires high up on towers.
One of the best things about disc insulators is that they’re budget-friendly and safe for the environment. Even if dust or rain tries to bother them, they still work well and protect the line. That’s why they are used a lot in outdoor electrical systems.

Main Insulating Materials in Electrical Work

In the world of electricity, safety is very important. To stop the flow of unwanted electric current, we use special materials called insulators. These materials do not let electricity pass through them easily. Let’s learn about some of the most common insulating materials used in electrical work:

1. Dry Air

Dry air is one of the best natural insulators. It does not allow electricity to flow through it. That’s why, in overhead electric lines, the space between the wires is filled with air. This air keeps the wires from touching each other and prevents any short circuits.
But there’s one thing to remember—moisture (water in the air) can reduce its insulating power. So, enough distance is always kept between the wires to keep them safe and dry.

2. Vulcanised Rubber

Vulcanised rubber is a man-made insulating material. It is made by heating regular rubber with sulphur and zinc oxide. This process makes the rubber stronger and more durable.
It is used to cover wires and cables so that electricity stays inside the wires and does not harm anyone.

3. PVC (Poly Vinyl Chloride)

PVC is another strong insulating material. It is tougher and longer-lasting than rubber. That’s why, in today’s time, PVC is used more often in place of rubber.
You can see PVC being used in most modern electric wires, cables, and household items. It keeps the wires safe and also protects people from electric shocks.

Abonite

Abonite looks and feels like hard rubber. It doesn’t catch fire easily but starts to burn only when the temperature goes above 180°C. It has 30% to 40% sulfur in it. The best part is — even strong acids can’t damage it. That’s why it is perfect for making things like battery shells, machine bodies, and panel boards.

Mica

Mica is a shiny, see-through material that is strong against fire, heat, and water. It does not allow electricity to pass through it, which makes it very safe. Mica is found naturally, and India has a lot of it. No other natural material can match mica when it comes to using it in electrical heaters. It stays strong, even in heat and wet conditions.

Micanite

Mica is strong, but it can break if you bend it. So, we turn it into micanite by sticking thin layers of mica onto paper or cloth using a special glue called varnish. Micanite is soft and bendy. It is used when we need flexible materials — like in the winding of armatures inside motors.

Bakelite

Bakelite is a hard and strong material. It does not let electricity pass through and can bear high temperatures. It’s made from special types of plastic called resins. It can be shaped easily and is used in making electrical items like switches, sockets, plug tops, bulb holders, and ceiling roses. You see it in your home almost every day!

Leatheroid Paper

This is a special grey-colored paper that does not get damaged by water, oil, or grease. It is safe and strong. It is used as a protective layer between coils and the slots in the armature — the spinning part inside electric machines.

Resin

Resin is an artificial or man-made material. It is used to make bakelite and also used to make strong, non-electric shells. These are called dielectric shells because they stop electricity from passing through.

Mineral Oil

Mineral oil is a thick, clean oil that comes from deep inside the earth through petroleum. It is very good at handling electricity. Unlike vegetable oils, it doesn’t lose its power when it gets old. That’s why it is used in transformers, big electric switches, starters, and capacitors — all places where high power is used safely.

Porcelain

Porcelain is a special kind of clay. It is shaped, dried, and baked to become strong and hard. Once ready, it does not let electricity pass through it, which makes it very safe to use. That’s why we use it to make things like insulators for electric wires, fuse holders, switches, and plates used with heating devices.

Glass

Glass is a shiny and clear material. It does not let electricity flow through it and is not affected by water or moisture. But it can break easily, so we don’t use it in switches. Still, it is very useful. We use it to make the outer covers of bulbs and tube lights. A special type called crown glass is even better at stopping electricity than regular glass.

Asbestos

Asbestos is a white, soft, and fibrous mineral. It doesn’t burn and can handle heat very well. But it can soak up water. It is used in things like electric irons and heaters to keep the heat in and the electricity safe.

Marble

Marble is a hard stone that is usually white. It doesn’t catch fire and can handle high heat. When ground into powder, it is used inside heating rods like immersion heaters to stop electricity from escaping. It is also used in places where the temperature can get very hot.

Shellac and Varnish

Shellac is a chemical that looks like a thick, shiny gum. When we mix it with a liquid called methylated spirit, it turns into a varnish. This varnish is used to coat things like paper, cloth, wood, and electrical windings. It helps keep out moisture and protects the material from getting damaged.

Paper as an Insulator

Paper is made from natural things like grass or cotton. It doesn’t conduct electricity, which makes it a great insulator. We use it in paper capacitors to stop current from flowing where it shouldn’t. There are different types of special papers like:

• Leatheroid paper
• Pressfan paper

Each one is made for a different purpose in electrical work.

Slate

Slate is a black stone. You may have seen it as an old writing board. But in electricity, we use slate in switchboards and panel boards. First, it is dipped in oil, and then a layer of varnish is applied to make it even safer and stronger.

Dry Wood

Dry wood is a natural insulator. It does not let electricity pass and also stops heat from spreading. That’s why it is used to make:

• Switchboards
• Round blocks
• Battens (used to fix wires neatly on walls)

Other Useful Insulating Materials

We can make many other types of insulators by using things like cotton, paper, and varnish together. These are shaped and prepared in different ways. Some common examples are:

• Fiber
• Pressfan paper
• Cotton tape
• Empire cloth
• Empire sleeve
• Hardboard

All of these help in different kinds of electrical work, from small devices to big machines.

Order of Insulation Strength

Not all insulators are the same. Some are stronger than others. The strength of an insulator is measured in kilovolts per millimeter (kV/mm). That means how much voltage it can stop from passing through 1 mm of the material. A list is usually made, showing which material is the strongest insulator at the top and the weaker ones below.

This helps electricians and engineers choose the right material for the right job.

These materials may all be different, but they have one thing in common:
They help make electricity safe, controlled, and useful for all of us.
Understanding them helps us know how electric machines are built and how they work safely.

Dielectric Strength of Insulators

What Does Dielectric Strength Mean?

Dielectric strength tells us how good a material is at stopping electricity from passing through it. A higher number means the material is better at stopping electricity, so it is a stronger insulator.

For example:

• Vulcanized rubber is very strong, so it’s great for electrical safety.
• Dry wood is not very strong, so it is not used where high electricity is involved.

Classification of Insulators Based on Temperature

In 1958, the Indian Standards Institute (ISI) created a simple way to classify insulating materials. This classification helps us understand how much heat an insulating material can safely handle without getting damaged.

This system is called BIS-1271 (1958/1985). It divides insulators into different classes, based on their maximum safe temperature.

Each class has a name (like Y, A, B, etc.) and a temperature limit. The higher the temperature limit, the stronger the material is against heat.

Let’s understand it step by step:

• Class Y is the weakest. It can only handle up to 90°C.
• Class C is the strongest. It can handle more than 220°C, even up to 250°C in some cases.

Simple Table for Classification

Properties of Electrical Insulators

Electrical insulators are special materials that do not allow electricity to pass through them. This is because the tiny particles inside them, called electrons, are held very tightly and cannot move freely.

Here are some basic and important properties of electrical insulators:

They do not let electricity flow.
This is the main reason we use them—to keep us safe from electric shocks.

They have high resistance.
That means they stop the flow of electric current very strongly.

They can handle high electric pressure.
This is also called dielectric strength. It helps the insulator to block electricity even when the voltage is high.

They allow air to pass around them easily.
This is good because it helps in cooling and reduces heat buildup.

Different insulators break down at different voltages.
Some can handle more electricity than others before they stop working. That’s why we choose different insulators for different electrical jobs.

Difference Between Conductor and Insulator

To understand how electricity works, it’s important to know about two types of materials — conductors and insulators. These two behave very differently when electricity tries to pass through them.

Below is a clean and simple comparison:

Advantages of Insulators

Stops Electric Current from Flowing
Insulators are made to stop electricity from passing through them. This helps us guide the electric current where we want it to go, safely and carefully.

Keeps People Safe
Insulators cover wires and electric parts so that no one accidentally touches them. This helps protect people from electric shocks and keeps the equipment safe too.

Works Well with High Voltage
Some machines and wires use very high voltage. Insulators are strong enough to handle this without breaking. This lets electricity flow with power, without any problem.

Saves Energy
Good insulators stop unwanted electric flow. This means less energy is wasted, and everything works more smoothly and efficiently.

Easy to Make and Shape
Materials like rubber, plastic, and glass can be easily shaped into insulators. They are not too expensive and can be made in many sizes and designs for different uses.

Disadvantages of Insulators

Work only in certain temperatures
Insulators do not like too much heat or too much cold. If it gets too hot, many insulators stop working properly. They are made to work within a limited range of temperatures.

Get dirty easily
Dust, water, and dirt can collect on the surface of insulators. When that happens, they don’t work as well. This means they need to be cleaned regularly to stay safe and strong.

Can fail if voltage is too high
Every insulator has a limit. If too much electricity passes through, it can break down and let the current flow through. This can be dangerous and must be controlled.

Easily damaged
Some insulators are not very strong. They can break or crack if dropped or used in rough conditions. Once damaged, they must be replaced to keep everything safe.

Adds extra cost and weight
Using insulators means spending more money. They also add weight and make the design of electrical systems more complex. Engineers have to plan carefully to include them in the right way.

Applications of Electrical Insulators

Electrical insulators are very important in our daily life. They help keep us safe from electric shocks by stopping the flow of electricity where it is not needed.

We see electrical insulators almost everywhere — in homes, schools, offices, and on the streets. They are mostly used to cover wires and other electrical parts that should not carry current on the outside.

If a live wire is not covered properly, it can be dangerous. If someone touches it, they might get a shock. That’s why we use electrical insulators — to block the electricity and protect people.

Here are some common uses of electrical insulators:

Wire Coating: Insulators are used to cover electric wires. This makes sure the electricity flows only through the wire and not outside it.

Electric Poles: You’ll often see insulators on electric poles. These keep the wires from touching the poles and help manage high voltages.

Appliances: Many of our daily-use appliances like irons, heaters, and mixers have insulators inside them. These keep the electric parts safe and help the machine work better.

Circuit Boards: Insulators help protect the circuits inside electronic devices, making sure they work smoothly.

Cables: Thick electric cables are covered with layers of insulating material to prevent fire and overheating.

High Voltage Areas: In areas with high voltage, special insulators are used to stop electricity from flowing to unwanted places.

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