Why aren’t electrical insulators just made from rubber and not worry about using other polymers? Would that be ultimately best for the environment?
Rubber is a great insulator if it’s pure rubber, but pure rubber is expensive and has some limitations, such as its density and weight compared with synthetic polymers. It’s easy to conceive that rubber is environmentally friendly, but it can take up to 80 years to biodegrade.
- 1 What makes a good electrical insulator?
- 2 Why are materials such as glass and rubber good insulators?
- 3 Difference Between Conductors and Insulators
- 4 Why are electrical wires coated with rubber?
- 5 Is silicone conductive to electricity?
- 6 Why are electric wires coated with PVC or rubber?
- 7 What is the best type of cable insulation?
- 8 What happens if the cable insulation fails?
- 9 Important Properties of Insulators
- 10 Why is dielectric strength important?
- 11 What is the dielectric strength of PVC?
- 12 How long does PVC cable last?
- 13 Are insulation sheaths colour coded?
What makes a good electrical insulator?
Strong structural matrix. Insulators need to have a strong bonded structural matrix that does not allow particles to bounce around and generate heat. In the case of electric insulation, it does not allow electrons to pass through the material.
When particles are held tightly together in the structural matrix, generating heat and transferring energy, such as charged electrons, known as electricity, is tough.
Other desirable properties of an electrical insulator would be cheap to the manufacturer and pliable in a wide temperature range for ease of installation.
Oxidation resistant and resistant to alkalis and acid chemicals. If you can add abrasion resistance, it would be a winning formula.
Why are materials such as glass and rubber good insulators?
The electrons are tightly bound. With glass and rubber, it makes it difficult for the electrons in those materials to move or be reactive to an outer stimulus such as heat or charged electrons.
Difference Between Conductors and Insulators
|Materials that conduct electricity are conductors.||Materials that do not conduct electricity are insulators.|
|In conductors, the electric field can only exist on the surface of the material but remains zero inside it.||In insulators, the electric field can neither exist on the surface nor inside the material.|
|The electric charge (electrons) can move freely inside the conductors.||The electric charge (electrons) cannot move freely inside the insulators.|
|They can store energy.||They cannot store energy.|
|They show very high conductivity and low resistance.||They show negligible conductivity and very high resistance.|
|The resistivity of conductors can vary from low to high.||Insulators have very high resistivity.|
|In the case of conductors, the covalent bonds are quite weak.||In the case of insulators, the covalent bonds are quite strong.|
|In conductors, the conduction band is full of electrons and the valence band is almost empty.||In insulators, the valence band is full of electrons and the conduction band is almost empty.|
|Due to the overlapping between the conduction and valence band. Hence, there is no forbidden gap in conductors.||Since there is no overlapping between the conduction and valence band, Hence, there is a large forbidden gap in insulators.|
|In the case of conductors, the temperature coefficient of resistance is positive.||In the case of insulators, the temperature coefficient of resistance is negative.|
|Examples of conductors include silver, aluminum, iron, etc.||Examples of insulators include rubber, wood, paper, etc|
Why are electrical wires coated with rubber?
Prevent electrocution. If copper electrical wires were exposed the first time they were touched, you would be zapped by the current flowing through the cable.
Electricity always takes the path of least resistance to earth, and if you touch a live exposed wire, the path to earth is you, hence, the electric shock.
Is silicone conductive to electricity?
It can be. Silicone in its purest form has excellent conductive properties and can be used as an insulator, efficiently protecting against electric shocks.
However, silicone is used as both an insulator and conductor in the semiconductor industry, so it depends on the silicone you use and how effectively it insulates in electricity.
Why are electric wires coated with PVC or rubber?
Insulation from electric shock. PVC makes the ideal insulator for cables. It’s pliable, resistant to alkalis and acids and has thermal properties that allow the PVC to be used in a wide band of temperatures.
PVC insulation offers a level of abrasion proofing. In addition, PVC can be used outside when clipped to a wall, and it has UV resistant properties.
Both rubber and PVC do not conduct electricity, making them the perfect choice for electrical insulation.
What is the best type of cable insulation?
Ethylene Propylene Rubber (EPR). EPR is widely used for its soft insulation. It’s frequently used in high voltage situations where excellent insulation is needed.
EPR may be soft, but it has excellent heat resistant properties. It resists oxidation, weathering and water, acid, and alkalis, making it a first-class choice for insulation.
What happens if the cable insulation fails?
Often you don’t know. Unless you receive an electric shock or an RCD keeps tripping, you may never know until you have an EICR check, which may be years away if it’s ever done.
Frequently on electrical installations, when using metal pattress boxes the wire is neatly wrapped and pushed back into the pattress. It’s normal practice.
The neutral can snag and cut the insulation. Or a homeowner hammers a nail into a stud wall for a picture frame and clips a cable. If it’s the neutral, you will just get a defective earth league on a test.
Important Properties of Insulators
- It’s important that the valence electrons are not allowed to move and must be bound tightly within the matrix structure of the material. No free electrons to conduct electricity
- Must have high electric resistance properties that do not allow the passage of electrons through the material. Insulation should not get wet, or the resistance can decrease in certain instances.
- The dielectric strength must be high. The dielectric strength is the maximum electric field the insulator can withstand without breaking down and becoming charged with electrons making it conductive
- Air permeability is a useful property for a good insulator. Air is a great insulator, and it enhances the properties of the insulation of the cable.
Why is dielectric strength important?
To withstand electrical fields. High-quality insulators can withstand high voltages. The dielectric coating is for the protection of the users and the overall strength of the insulation in terms of not becoming conductive.
Pure rubber has a high dielectric rating. This is why it is used by linemen working with high voltages.
What is the dielectric strength of PVC?
Dielectric strength values of four plastics:
|Polymer Name||Min Value (kV/mm)||Max Value (kV/mm)|
|PVDF – Polyvinylidene Fluoride||10.00||27.00|
|SAN – Styrene Acrylonitrile||12.00||24.00|
|SAN, 20% Glass Fiber-reinforced||19.70||20.00|
It’s easy to identify that PVC has excellent insulation values. This is why so many cables have PVC insulation coatings.
How long does PVC cable last?
Indefinitely if not misused. Tube working lifetime of a PVC insulation sheath is indefinite and, in real terms, could last a lifetime without degradation if not misused.
This is why twin and earth cable is frequently insulated with PVC sheathing.
Are insulation sheaths colour coded?
Yes, there is the standard Brown (live), Blue (neutral) and Green- brown (earth). But there are many other colour variants:
The colours shown are from BS7671 Table 51
|Protective conductors||Green and Yellow|
|Functional earthing conductor||Cream|
|AC Power Circuit|
|Line of single-phase circuit||L||Brown|
|Neutral of single- or three-phase circuit||N||Blue|
|Line 1 of three-phase AC circuit||L1||Brown|
|Line 2 of three-phase AC circuit||L2||Black|
|Line 3 of three-phase AC circuit||L3||Grey|
|Two-wire unearthed DC power circuit|
|Positive of two-wire circuit||L+||Brown|
|Negative of two-wire circuit||L-||Grey|
|Two-wire earthed DC power circuit|
|Positive (of negative earthed) circuit||L+||Brown|
|Negative (of negative earthed circuit²||M||Blue|
|Positive (of positive earthed circuit²||M||Blue|
|Negative (of positive earthed circuit||L-||Grey|
|Three-wire DC power circuit|
|Outer positive of two-wire circuit derived from three-wire system||L+||Brown|
|Outer negative of two-wire circuit derived from three-wire system||L-||Grey|
|Positive of three-wire circuit||L+||Brown|
|Mid-wire of three-wire circuit²,³||M||Blue|
|Negative of three-wire circuit||L-||Grey|
|Control circuits, ELV and other applications|
|Line conductor||L||Brown, Black, Red, Orange, Yellow, Violet, Grey, White, Pink or Turquoise|
|Neutral or mid-wire4||N or M||Blue|