Knowing how to size cables is important for any electrical installation. Cable size is typically identified by its cross-sectional area (measured in square millimetres) or its diameter, which influences how much current the cable can safely carry.
The appropriate cable size supports system efficiency, helps prevent overheating, and ensures compliance with electrical safety regulations. The following points outline the main factors you should consider.
Advantages of Calculating the Correct Cable Size
Using the right cable size starts with knowing how to size cables through accurate calculation. This step helps align system design with load requirements, installation conditions, and long-term performance goals.
Prolongs the life of your electrical cables
To prevent heat accumulation and physical damage, select a cable with an ampacity (maximum current-carrying capacity) that accommodates the full load current and potential short-circuit current. Proper sizing reduces thermal stress and prolongs the operational life of electrical cables.
Less voltage drop
Operating electrical equipment outside its specified voltage range can lead to premature failure and hazardous conditions. Voltage drop occurs when an undersized cable creates excessive impedance, lowering the power supply output voltage to unsafe levels. The magnitude of voltage drop depends on the cable’s impedance, load current, and load power factor.
Refer to AS/NZS 3008 cabling standards to determine acceptable voltage drop limits for maintaining efficient electrical performance in Australia.
Fewer expenses
Oversized cables increase material expenses unnecessarily. Since cable cost rises with conductor diameter, avoid exceeding the size required for safe and efficient operation to maintain budget efficiency.
Main Factors in the Cable Selection Process
After understanding the importance of selecting the correct cable size, it’s important to review the primary factors involved in how to size cables properly. These factors serve as a foundation before exploring the three main considerations when choosing cable sizes.
Current-Carrying Capacity
This factor is important in installations with short cable route lengths, such as residential settings. It depends on installation type and external conditions, including thermal insulation, which influences cable operating temperature and ampacity.
Voltage Drop
Its limitation is often the deciding factor for longer cable route lengths. This key component relies on a cable’s impedance, the magnitude of the load current, and the load power factor.
Short-Circuit Temperature Limit
Rarely a primary sizing factor, this depends on the energy generated during short-circuit events and ensures cables withstand thermal and mechanical stress without damage.
3 Things to Consider When Choosing Cable Sizes
The goal is to select the smallest cable size that meets all operational conditions and prevents cable overload:
1. Type of Power Supply
Differentiate between alternating current (AC) and direct current (DC) power supplies, as their current-carrying capacities vary. AC current flows primarily on the cable surface (skin effect), whereas DC current flows uniformly through the conductor, generating lower heating effects.
Additionally, AC systems may use single-phase or three-phase configurations, while DC systems generally use two poles.
2. Load Type and Amount of Current
Specify the load in terms of amps, watts, kilowatts, or horsepower when calculating cable size. Undersized cables risk overheating and failure, while oversized cables, especially in commercial systems, may cause fault currents to exceed protective device ratings, creating safety hazards.
3. Derating Factors
Cable arrangement and ambient air temperature impact heat dissipation and cable operating temperature. Poor layout or tight bundling reduces ampacity by increasing heat buildup. Applying derating factors in cable sizing calculations adjusts for these conditions. This ensures cables operate safely and maintain their performance within specified limits.
Experienced electricians and engineers understand that how to size cables accurately involves evaluating multiple parameters beyond basic criteria. These include insulation type, installation method, and environmental conditions to ensure proper cable performance and safety.
Get Started with Accurate Cable Sizing Today
Accurate cable sizing ensures electrical system safety, efficiency, and longevity. You can select the most appropriate cable size for each application by carefully considering factors such as power supply type, load requirements, derating conditions, and installation environment.
Applying these principles minimises risks like overheating, voltage drops, and unnecessary costs while maximising performance. Use the free CableHero web and mobile app to access a comprehensive, user-friendly cable sizing calculator. Simply register to start optimising your electrical designs today!
Disclaimer: While CableHero provides accurate and helpful information, it does not guarantee completeness or suitability for every application. Users assume responsibility for their own calculations and installations.
Frequently Asked Questions (FAQs)
If you want to know more about how our cable calculator can help you, check out these details:
How to calculate cable cross-sectional area?
To calculate the cable cross-sectional area, divide the current load by the allowable current density for the conductor material. Alternatively, you can use a cable size calculator to find the appropriate area based on current and installation conditions.
What are the consequences of ignoring cable sizing standards and regulations?
Non-compliance can lead to electrical hazards, equipment failure, increased maintenance costs, and legal penalties. Adhering to standards ensures reliability and protects people and property.
