Electrical Resistance Wire

Electrical resistance wire is a type of wire specifically designed to resist the flow of electricity. This property allows it to generate heat when an electrical current is passed through it. The wire is made from materials with high resistivity, such as Nichrome (a nickel-chromium alloy), ICA 135 and ICA 145 (iron-chromium-aluminum alloys), Copper Nickel alloys, and sometimes pure metals like tungsten and molybdenum. 

It is used in a variety of applications, such as heating elements, resistors, and specialised electrical circuits.

Electrical resistance wire works by resisting the flow of electrical current through it, which in turn generates heat as a byproduct.  When an electric current is applied to resistance wire, the electrons moving through the wire collide with the atomic lattice of the wire material, causing resistance to the flow of electricity. This resistance converts electrical energy into heat energy, a principle known as Joule heating. The amount of heat generated is proportional to the square of the current, the resistance of the wire, and the time for which the current is applied.  This heat can be used in applications such as heating elements.

Common materials used in electrical resistance wire include nichrome, iron chrome aluminium alloys and copper-nickel alloys. These materials are selected for their specific resistive properties and high melting points. 

Stainless steel alloys can also be used for low temperature resistance wire in applications where high strength is required.

Electrical resistance wire has a diverse range of uses, ranging from automotive, aerospace, electronic, medical and scientific industries.  It is commonly used for industrial applications, including heating elements, kilns, cutting, and sealing processes in machinery.  Domestic applications include many common household items such as electric ovens, toasters, floor heating systems and resistors in electronic circuits.  Resistance wire is used a range of Medical and Scientific applications and can be found in surgical tools and equipment, and in scientific laboratories for experimental setups.

Selecting the right resistance wire depends on several factors, including the operating temperature, whether the environment is corrosive or non-corrosive, the required life span, and the electrical properties needed. For high-temperature applications, alloys like ICA135 and ICA 145 may be preferred due to their higher melting points. However, for environments where corrosion is a concern, Nichrome could be a better choice due to its superior corrosion resistance.

To help you decide:

• Consider factors like resistance value, wire diameter, material properties, and operating temperature when selecting wire.
• Compare types of resistance wire based on temperature range, resistance stability, and durability.

If you need further assistance, contact our dedicated wire sales team using either our contact form, telephoning 01707 645261 or wire.sales@knight-group.co.uk. 

The resistance of a wire is affected by its length, diameter (or cross-sectional area), material composition, and temperature. Specifically:

• Length: The longer the wire, the higher its resistance.
• Diameter/Cross-sectional area: A thinner wire has higher resistance than a thicker wire.
• Material: Different materials have different resistivities, affecting the wire’s resistance.
• Temperature: As temperature increases, resistance typically increases for metallic conductors.

In simple terms:

Resistance is directly proportional to wire length : The longer the wire, the higher its resistance.

As the length of the wire increases, the path that electrons must travel becomes longer, resulting in more collisions between electrons and the wire’s atoms. These collisions increase the resistance of the wire. Assuming the resistivity and cross-sectional area remain constant, as the length of the wire increases, the resistance also increases. For example, a longer wire will have more resistance than a shorter wire with the same material and cross-sectional area. It is important to consider the length of the wire when designing electrical circuits to ensure proper current flow and efficient operation.

In simple terms:

Resistance is inversely proportional to a wire’s cross-sectional area

According to Ohm’s law, resistance (R) is inversely proportional to the cross-sectional area (A) of the wire. The cross sectional area of wire directly impacts the flow of electrons through the wire.  A larger cross-sectional area provides more room for electrons to move, reducing the likelihood of collisions with the atoms of the wire material. Consequently, a wire with a larger cross-sectional area allows for easier and smoother electron flow, resulting in lower resistance.  Therefore, as the cross-sectional area of a wire increases, its resistance decreases, assuming the length and material of the wire remain constant.

Example: Two wires A and B are made of the same material with equal lengths. Wire A has a larger cross-sectional area than wire B. Due to its larger area, wire A will have lower resistance compared to wire B.

It is essential to understand the relationship between cross-sectional area and resistance when designing electrical circuits. Using wires with an appropriate cross-sectional area helps to minimise resistance, optimise current flow, and ensure efficient operation.

Yes, resistance wire is commonly used in temperature control applications. Its resistance changes with temperature, a property that can be used to monitor and regulate temperature. In some applications, a feedback loop is used with a temperature sensor to adjust the current through the wire, maintaining a desired temperature.

The power output (in watts) can be calculated using Ohm’s Law and the power formula: Power (P) = Voltage (V)² / Resistance (R)

Alternative formulas: P = I²R or P = V²/R

I is the current in amperes
R is the resistance in ohms

This calculation helps in designing heating elements to ensure they produce the required amount of heat.

To calculate the length of wire needed to achieve a specific resistance, you can use the formula: L = ( R × A )​ / ρ

$L$ is the length of the wire
$R$ is the desired resistance
$A$ is the cross-sectional area of the wire
$\rho$ is the resistivity of the wire material.

It’s crucial to use consistent units (e.g., ohms for resistance, meters for length, square meters for area, and ohm-meters for resistivity) and to know the resistivity of the wire material.

The resistance of a wire can be calculated using the
formula: Resistance (R) = ρ x ( L / A )
where ρ is the resistivity of the material, L is the length of the wire, and A is the cross-sectional area of the wire.

R is the resistance in Ω;
ρ is the resistivity of material in Ω × m;
L is the length of the wire; and
A is the cross-sectional area of the wire.

Maintenance requirements for resistance wire depend on its application and operating environment. Regular inspections for physical damage, corrosion, and degradation of insulation (if applicable) are recommended. In some cases, cleaning to remove any accumulated dust or debris may be necessary, especially in environments where contaminants could affect the wire’s performance or lead to premature failure.

Signs of failure in resistance wire include physical damage such as cracks, breaks, or significant thinning; a reduction in heating efficiency; discolouration beyond normal oxidation; and in some cases, electrical shorts or open circuits. Regular monitoring and maintenance can help identify these issues early, preventing potential safety hazards or equipment downtime.

Yes, resistance wire can be cut to the desired length, joined or extended. However, it requires careful consideration and it is important to maintain the integrity of the wire to ensure a reliable and safe connection for proper functioning. Methods for joining resistance wire include soldering (for some alloys), welding, and using specialised connectors or splices designed for high temperatures. The chosen method should maintain the integrity of the wire’s resistance characteristics and withstand the operating temperatures.

When using resistance wire, it is important to ensure that the wire is properly insulated and mounted to prevent any accidental contact, which could lead to burns or electrical shocks. Additionally, the wire should not be overloaded beyond its maximum temperature and power ratings to avoid damage or fire hazards. Always follow safety standards and regulations applicable to your specific application.

Disposal of resistance wire should follow local environmental regulations and safety guidelines. Since resistance wire can contain metals such as nickel and chromium, it should not be disposed of with common refuse. Recycling is the preferred method of disposal, and many metal recycling centres accept resistance wire. Always check with local waste management services for proper disposal methods to ensure environmental compliance.

You can purchase high-quality electrical resistance wire from Knight Precision Wire. Knight Precision Wire, a division of the Knight Group, is a specialist manufacturer of wire and cable. We offer free quotations on your requirements and can provide expert advice on selecting the right resistance wire for your application.

Knight Precision Wire are specialist wire and cable manufacturers and can provide free quotations on your requirements. You can use our contact form, 01707 645261 or wire.sales@knight-group.co.uk.