Does Proper Bolt Torque in Electrical Connections Matter?
Select Switchboards │ Last Updated: 03/02/25
When it comes to electrical connections in switchboards, correct bolt torque is a crucial detail that impacts both performance and safety. Over- or under-torqued bolts can lead to excessive joint resistance, overheating, and even connection failure. Despite appearing simple, fastening a bolt requires precision—especially as torque requirements can vary depending on application, bolt material, and configuration. This article explores why proper torque is essential, the factors that influence torque requirements, and best practices to ensure secure and reliable electrical connections.
Why Bolt Torque Matters for Electrical Connections
Bolt torque creates the pressure that holds two connecting surfaces together. In electrical connections, this pressure helps reduce joint resistance, which is the electrical resistance at the interface between two conducting surfaces. However, the relationship between torque and resistance isn’t straightforward; while increasing torque reduces resistance initially, further increases can bring diminishing returns. Beyond a certain threshold, additional torque brings little benefit and can even cause metal deformation or creep, damaging the joint. Get In Touch if you'd like assistance with selecting the appropriate torque setting for your connections.
Always Refer to Manufacturer Recommendations First
A key step when working with electrical connections is to follow the manufacturer’s torque recommendations, particularly for component terminations. Manufacturers set torque values based on material properties, safety margins, and the application. This is especially important as some components may use bolts made from softer materials like copper or brass, which have a lower torque threshold than high-tensile steel bolts. Over-torquing these softer bolts can lead to thread stripping, bolt deformation, or damage to the connection surfaces. Always consult and adhere to manufacturer guidelines for optimal performance and safety.
Pressure vs. Resistance: A Nonlinear Relationship
A specific amount of pressure—achieved through correct bolt torque—is essential for maintaining a low-resistance joint. However, this relationship is nonlinear. Once the optimal contact pressure is reached, further tightening offers only marginal reductions in resistance, while the risk of damaging the connection surfaces increases. That’s why finding and maintaining the correct torque is crucial; too much pressure can create unnecessary stress on the bolt or metal connection without improving conductivity.
Avoiding the Risks of Over-Tightening
One common risk during installation is over-torquing bolts, which can occur if a fitter applies excessive force or uses a larger-than-necessary spanner or torque wrench, providing additional leverage. This can lead to an improperly high torque that may seem deceptively low when using such tools. Exceeding the recommended torque can result in deformation of the bolt threads or the connected materials, especially with softer metals, ultimately compromising the connection. To avoid this, use a torque wrench set to the recommended value and avoid applying extra force.
Accounting for Environmental and Operational Factors
Bolt torque values are usually set at room temperature, while standards like AS61439 permit busbars to operate at temperatures exceeding 100°C. Thermal expansion rates of different materials, such as copper busbars and steel bolts, vary, impacting the applied pressure at elevated temperatures.
Thermal Expansion Differences: Copper and steel have distinct expansion rates. Copper has a linear thermal expansion coefficient of approximately 17 x 10⁻⁶ /°C, while steel is about 11–13 x 10⁻⁶ /°C. This difference causes copper to expand more rapidly under heat. When in operation and the increases in temperature from ambient when it the bolt was torqued, copper busbars expand more quickly than steel bolts. This can increase pressure on the bolt as copper expands, potentially pushing it beyond optimal torque levels.
Mechanical Fatigue and Creep: High temperatures and constant pressure can cause metals to deform over time, a phenomenon known as “creep.” Thermal cycling can amplify these effects, loosening the bolt and impacting joint stability over time.
The Role of Washers in Connection Stability
Washers are a critical element in achieving stable and secure bolted joints. Spring washers or Belleville (conical) washers are commonly used in electrical connections as they provide a cushioning effect, which allows for lower torque without risking loosening. These washers maintain pressure on the bolt, reducing the risk of it coming loose even under thermal cycling or vibration. Conical washers are particularly effective in high-temperature applications, as they accommodate the expansion and contraction of metals, helping maintain secure pressure over time.
Best Practices for Torquing Bolts in Electrical Connections
Correct torque minimizes joint resistance, reduces energy loss, and improves long-term stability in electrical systems. Following these best practices can help ensure reliable connections:
Apply Manufacturer-Recommended Torque Values: Always follow the manufacturer’s specifications, especially when working with non-steel bolts or softer materials. Using a torque wrench ensures consistent and precise application.
Use Appropriate Tools: Avoid using oversized spanners or torque wrenches, impact guns or drills, which can make it easy to exceed recommended torque values unintentionally.
Incorporate Washers for Stability: Select washers suitable for the connection. Spring washers and Belleville washers offer additional stability and help retain pressure in high-vibration or thermal cycling environments.
Consider Environmental and Operational Factors: Select bolts, washers, and torque values that account for the connection’s maximum operating temperature and the materials’ thermal expansion properties.
Inspect and Retorque as Needed: Regular inspections and retorquing, especially in high-temperature or vibration-prone environments, can help maintain optimal connection performance.
Achieving the correct bolt torque in switchboard assemblies is not just about securing parts; it’s a balance that keeps electrical connections safe, efficient, and durable. Properly executed, it minimizes joint resistance, prevents long-term wear, and enhances the reliability of electrical systems in challenging operational environments.
Are you ready to ensure your switchboards are up to standard and future-proof your electrical installations? Whether you're looking to Design A New Switchboard System, Upgrade An Existing Switchboard, or simply seek advice on AS/NZS 61439 compliance for your project, Get In Touch With Our Team At Select Switchboards Today!