Resistance wire is an alloy wire which produces some level of resistance to an electric current.
This resistance may be used for numerous reasons, including to control the flow of electricity or the amount of current in a circuit, and also as a heating element. The resistance of the wire, while it is conducting electricity, can generate heat, which is utilised in various products such as heaters, toasters, and hairdryers.
Other domestic applications where resistance wire is used include remote controls, light bulbs, and phone chargers, each of which has a high voltage and is a conductor of heat, so requires a high electrical resistivity to properly function.
The Resistance Of Wire Explained
Resistance Wire Applications
However, resistance wire is not just used in domestic applications, despite these examples of everyday items. Resistance wire can be found across a range of industries and applications, including automotive and aerospace applications.
The quality of resistance wire is tightly controlled by BS 115 requirements (and BS 117, which outlines its required cross-sectional area and states that the diameter of a wire must be less than 0.32mm) because of the many uses of resistance wire and its widespread applications.
Depending on the application, the combination of metals used within the resistance wire will change to increase or decrease resistance, or to suit the environment of its application – such as temperature. No matter of the alloy, resistance wire can be commonly found in varying lengths, from several metres to the great coils necessary for industrial use.
Still got questions regarding the resistance of wire? Let’s break it down further…
What Is Resistance Wire Used For?
Resistance wire uses include electrical resistors, which are used within electronics and electrical circuits for various control measures.
Some examples include: temperature control; control of current (both fixed and variable); and to stop a circuit from shorting – this type of resistor is known as a fusible resistor.They can also be used for heating and lighting functions.
Resistance wires can be used for domestic, commercial, and industrial applications alike, relevant in industries spanning from oil and gas and industrial heating, to the medical sector.
Factors Affecting Resistance of Wires
There are four main factors which affect the resistance of wire; these should all be considered when calculating the overall resistance of wire. Resistance factors include:
The material the wire is made from – the natural resistivity of your material selection will determine its overall resistance. For instance, copper wire is more conductive than steel, so would have a lower resistance to an electrical current.
Length of the wire – resistance is directly proportional to the length of a wire. The longer the wire, the higher the amount of resistance to an electrical current; this is known as a proportional relationship since resistance increases as length increases. This is influenced by the area of the wire. The longer the length of wire, the more likely the electrons that move and carry the electric current are to collide with ions throughout the wire, making it more difficult for the current to flow.
Thickness – thickness or gauge, also known as the wire’s diameter or cross-section, has an inversely proportional relationship to resistance. The thinner a wire is, the greater resistance it has; this is because a thinner wire has fewer electrons to carry an electric current.
Temperature – resistance changes as a wire is heated up. A hotter wire will have a larger resistance because this increases its vibration, making it harder for electrons to carry the electric current without interruption from atoms.
Resistance vs Resistivity
Though resistance and resistivity are closely related, they should not be used interchangeably since they refer to different measurements and resistance factors.
Electrical Resistance – marked by the symbol R – measures the overall resistance of wire. This includes resistivity, length, temperature, material, and gauge or thickness. Resistance is measured in Ohms.
Resistivity, on the other hand, refers to the natural resistance of a material or substance only. Resistivity is represented by the symbol ρ, and this measurement will not change as length or thickness changes. Resistivity is measured in Ohms-metres.
Though resistance and resistivity are separate measurements, they are proportionally related – the greater the natural resistivity of a material, the greater its overall resistance to an electric current.
Resistance Wire Types
Resistance wire types refer to the combinations of metals within the wire which create the alloy. The most common type of resistance wire is a nickel and chromium alloy which is used in heating applications. Other common types include constantan (a copper and nickel alloy) which is easily soldered and a copper, manganese and nickel alloy.
Scott Precision Wire offers several resistance wire types, meeting all industrial needs. Our range of resistance wire includes:
- Copper Magnesium: 0.2%; a high-strength alloy
- Copper and nickel alloys: created for low to medium-temperature heating applications, with good corrosion resistance
- Cromaloy 1: for good corrosion resistance and high-temperature applications
- Cromaloy 5: good resistance to oxide scaling and suitable for a range of applications from industrial furnaces to domestic toasters
- Cromaloy A: great for high-temperature applications with good resistance to Sulphur corrosion
- Cumin 11: a copper-based alloy with manganese and nickel, which is suited for DC circuitry
- Cupronic 2.5: a copper-based alloy with low resistivity, suitable for low-temperature applications
- Kutherm 3 & 10: a copper-based resistance wire, with elevated corrosion resistance and temperature resistance properties
- Nickel 205: suitable for high-temperature applications
- Nickel Iron alloys: a self-limiting heating wire for increased temperature control
- Stainless steel 304L: a low-temperature resistance wire with high strength
For further information regarding Scott Precision Wire’s resistance wire types consult our technical data downloads, or speak to an expert member of our team directly.
Wire Resistance Calculator
How do you calculate the resistance of a component? As established when identifying resistance factors, the overall resistance of a wire can be calculated by identifying the resistivity, length, and thickness of a wire. It is proportional to the cross-sectional area of the material compared to its natural resistivity. A resistance calculator will use these factors to calculate overall resistance.
However, this can also be done manually. The wire resistance formula used to calculate this is: resistance (R) = resistivity (ρ) multiplied by the division of wire length (L) over the cross-sectional area (A), or R = ρ (L / A).
Connecting Wires within a Circuit
Connecting wires can be used within a circuit; connecting wires resistance should not affect the circuit and they are assumed to have zero resistance, therefore connecting wires should have a low resistance. Copper is commonly used as a connecting wire since it is a highly conductive material.
When connecting wires within a circuit, it is important to ensure that they are properly connected within a terminal, as loose connections or poor soldering could lead to higher resistance and cause electrical inefficiencies or potential hazards. Additionally, connecting wires should be sized appropriately for the amount of current they will be carrying. If wires are too thin or small for the amount of current, this may impact the object's current flow, which could cause it to heat up and cause a fire.
