It is commonly used to create heat in a heating element - although, before the advent of solid-state controls, it was used to regulate the current in electrical circuits. Heating elements are found in space heaters, toasters, cookers and hair dryers.
Electrical resistance heaters are also used in many industrial environments including electric smelting furnaces and food processing machinery, as well as in the automotive sector for preheating components in internal combustion engines to reduce emissions when they start up.
The Resistance Of Wire Explained
Factors Affecting Resistance Wires
There are four main factors which affect the resistance of a wire which all need to be considered when calculating the overall resistance of wire.
- The material the wire is made from: The intrinsic resistivity of the material will determine the overall resistance. This is a material property and is unaffected by the geometry of the wire. For instance, a Copper-Nickel alloy will have a lower resistance (higher conductance) than a Nickel-Chrome-Iron alloy because its resistivity is lower.
- Length of the wire: Resistance is directly proportional to the length of the wire used. The longer the wire the higher the resistance.
- Diameter: The cross-sectional area of the wire has an inversely proportional relationship to the resistance. The thinner the wire, the higher the resistance.
- Temperature: Resistivity (and hence resistance) change when the wire is heated up. The metal atoms in the lattice vibrate more when heated and increasingly interrupt the flow of electrons as they travel along the wire.
Resistance Wire Types
Resistance wire types are created by using different combinations of metals to derive alloys with specific electrical properties. Commonly used alloys include high-temperature Iron/Chromium/Aluminium alloys, Nickel/Chromium alloys and lower temperature Copper/Nickel alloys.
Scott Precision Wire offers a wide range of resistance wire types meeting all your requirements, including:
- Resistance Copper: Pure copper wire manufactured to tight resistance specifications for low-temperature applications.
- Cupronic 2.5: A copper-based alloy with low resistivity suitable for low-temperature applications.
- Copper/Nickel alloys: Created for low to medium-temperature applications with good corrosion resistance.
- Kutherm 3 & 10: Copper based bronze alloys with elevated corrosion resistance and temperature resistance properties.
- Nickel/Iron alloys: Alloys with enhanced positive temperature coefficient properties for increased self-limiting effects.
- Stainless Steel 304L: A low to medium temperature resistance wire with high strength.
- Cromaloy 1: For good corrosion resistance in 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.
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
The nominal resistance of a wire can be calculated using the following wire resistance equation, where:
ρ = Resistivity
l = Wire length
A = Cross-sectional area
Resistance (Ohms) = (ρ x l) / A
However, as resistivity and size units can be varied (Ω.m, µΩ.cm etc) for a round wire the following resistance of wire formula can be used:
ρ = Resistivity in µΩ.cm
l = Wire length in m
d = Solid Wire diameter in mm
Resistance (Ohms) = (ρ x l) / (25 x π x d²)
Please contact Scott Precision Wire for assistance if you would like help in calculating the right values for your application.
Connecting Wires within a Circuit
If the resistance wire is being used as a standard resistor in an electronic circuit, then copper or tinned copper wires can be used. Copper has one of the lowest resistivities and will, therefore, not add significant resistance to the circuit. If you are connecting a heating element then pure Nickel or the slightly stronger 2% Manganese Nickel will be needed to cope with the higher temperature the lead wires will experience. Lead wires must be large enough to carry the current drawn by the elements, with Nickel wires having to be in the region of double the cross-sectional area of copper wires because of their higher resistance.
It is also important to make sure the terminations are fixed firmly to avoid hotspots occurring which could be a fire risk.