How to Size Busbar Trunking: Current, Short-Circuit, and Voltage Drop

You size busbar trunking by considering current rating, short-circuit withstand, and voltage drop. Accurate sizing keeps your power system safe and efficient. DELIXI Electric offers a power distribution solution that includes advanced busduct products and strict safety measures. When you ignore proper sizing, you risk system failures and safety issues. Trust DELIXI to help you meet safety standards and protect your facility.

Key Takeaways

• Always size busbar trunking by checking the current rating, short-circuit withstand, and voltage drop to ensure safety and efficiency.

• Use manufacturer data to calculate voltage drop and keep it within recommended limits to avoid equipment malfunctions.

• Plan for future expansion by selecting a busbar with a higher current rating than your current needs to save on costly upgrades later.

• Regularly inspect and maintain your busbars to catch issues early and extend their service life.

• Follow industry standards like IEC 61439-6 to ensure your installation meets safety and performance requirements.

Introduction

What This Guide Covers

You want to make sure your electrical system works safely and efficiently. This guide gives you clear steps for sizing busbar trunking in your projects. You will learn how to select the right current rating, check short-circuit withstand, and calculate voltage drop. Each step follows industry guidelines and uses real-world examples. You will see how to use busduct data from manufacturers like DELIXI Electric. You will also find practical tips for installation and maintenance. If you work with power distribution, this guide will help you avoid common mistakes and meet all safety requirements.

Tip: Keep this guide handy when you plan or review your next project. It can save you time and help you make better decisions.

Why Sizing Busbar Trunking Matters

You need to size your busbar trunking correctly to protect your equipment and people. If you choose the wrong size, you risk overheating, voltage loss, or even fire. Proper sizing keeps your system reliable and helps you follow safety standards. You also save money by avoiding costly repairs or downtime. When you use the right busduct, you improve the performance of your power system. DELIXI Electric designs products that meet strict standards, so you can trust their solutions for your projects.

Note: Always follow the latest safety codes and check with experts if you have questions about your installation.

What Is Busbar Trunking Sizing?

Definition and Scope

When you size busbar trunking, you determine the right dimensions and ratings for a system that carries electrical power safely and efficiently. This process involves checking the current-carrying capacity, short-circuit withstand, and voltage drop for your installation. You use busbar trunking in many settings, such as factories, commercial buildings, and data centers. Unlike cable sizing, you focus on a single, rigid system instead of multiple flexible wires. You also consider the physical space, installation method, and future expansion needs. Busduct systems help you organize and distribute power with fewer complications than traditional cables.

Aspect	Busbar Trunking	Cable Sizing
Space Requirements	More compact, e.g., 1600A busbar riser needs 185mm x 180mm	Requires more space, e.g., 20 cables for high current ratings
Installation Complexity	Simpler installation, assess a single riser	Complex, requires environmental assessment and individual protection
Flexibility	More adaptable, can be relocated easily	Physically flexible but challenging to modify once installed
Efficiency	Higher efficiency in limited spaces	Less efficient in space-constrained environments

Applicable Standards (IEC 61439-6, IEC 61439-1)

You must follow strict standards when you design and install busbar trunking. The main international standards are:

• IEC 60439-2: This standard defined busbar trunking systems since 1993.

• IEC 61439-6: This is the current standard since 2013. It covers definitions, service conditions, construction, technical characteristics, and verification for busbar trunking systems.

These standards require you to check several key areas:

Requirement Type	Details
Mechanical Construction	Enclosures must withstand mechanical impact (IK rating, e.g., IK08 for resistance to shocks).
Degree of Protection (IP)	Ensures protection against dust, water, and solid objects. Common ratings: IP54, IP65.
Testing Requirements	Two types: Type Tests (Design Verification) and Routine Tests (Final Assembly).
Type Tests	Includes temperature rise, dielectric strength, short-circuit withstand, verification of protection levels, and mechanical operation.
Routine Tests	Involves visual inspection and electrical continuity of protective circuits.

Tip: Always check the latest version of these standards before starting your project. This helps you stay compliant and safe.

Why Choose Busbar over Cables

You gain many advantages when you use busbar trunking instead of traditional cables for large-scale power distribution. Busbar systems offer faster installation, save space, and make future changes easier. You can add or move loads without shutting down the whole system. Their rigid design and standardized connections also improve reliability and reduce voltage drops.

Advantage	Description
Faster Installation	Busbar systems can be installed more quickly than traditional cables.
Space Efficiency	They save physical space, allowing for reduced riser sizes and improved maintenance access.
Flexibility for Modifications	Busbar systems allow for easy addition or relocation of loads without de-energizing the system.
Enhanced Reliability	Their rigid design and standardized connections lead to lower voltage drops and increased reliability.
Lower Total Cost of Ownership	Overall, busbar systems can result in a lower total cost of ownership compared to traditional cables.

You can see why many modern facilities choose busduct solutions for their main power distribution needs.

Pre-Design Checklist

Before you start your busduct system design, you need to review several important factors. This checklist helps you meet all design requirements and ensures your installation works safely and efficiently.

Route and Length

You should map out the route for your busbar trunking. Measure the total length from the supply point to every load. Longer runs increase voltage drop and affect the minimum size of busbars. Plan for straight paths when possible. Avoid sharp bends, as these can make installation harder and increase losses. If your route passes through fire barriers or different building zones, note these areas for special protection.

Load Profile and Diversity

You must know the load profile for your system. List all equipment and their power ratings. Check if loads run at the same time or if some operate only during peak hours. Use diversity factors to estimate the real current demand. This step helps you avoid oversizing or undersizing your busduct. Accurate load data supports better design and cost control.

Short-Circuit Levels

You need to calculate the short-circuit levels at each point in your system. Use the following table to understand the main parameters:

Parameter	Description
Isc	Three-phase short circuit current at a specific point
U	Phase-to-phase voltage at the fault point before the fault occurs
Zcc	Equivalent upstream system impedance
Zsc	Impedance of all series and parallel units upstream
Ssc	Short-circuit power at the distribution system join
Za	Equivalent impedance upstream from the point of interest

Short-circuit current depends on the voltage and the total system impedance. You must match your busbar trunking rating to the highest fault level expected.

Environmental Conditions

You should check the environment where you plan to install the busduct. Environmental factors affect current carrying capacity, voltage drop, and insulation. Consider these points:

• High temperature can reduce the current rating.

• Humidity and pollution increase the risk of flashover.

• Dust and moisture require higher IP-rated enclosures.

• Fire resistance is important for safety.

• Insulation and enclosure protect against accidental contact.

If your installation is in a harsh area, adjust your design requirements to include extra protection.

Material Choice (Copper vs Aluminum)

You need to choose the right material for your busbar trunking. Copper and aluminum have different electrical and mechanical properties. Review the table below:

Property	Copper	Aluminum	Copper Clad Aluminum (30%)
Conductivity (MS/m)	58.0	37.7	85%-92% of pure copper
Resistivity (μΩ-cm)	1.72	2.82	2.05
Carrying Capacity Ratio	100%	78%	89%
Density (g/cm³)	8.96	2.70	N/A
Cost ($/ton)	8400	2300	N/A

Copper offers higher conductivity and strength, but aluminum costs less and weighs less. Composite busbars provide a balance between cost and performance. Your choice affects the design, installation, and long-term efficiency of your power system.

Tip: Always match your material choice to your project’s design requirements and budget.

Step 1 — Select the Current Rating (In)

Understanding Continuous Current Rating

You need to start by determining the continuous current rating for your busbar trunking system. This rating tells you how much current the busduct can safely carry without overheating during normal operation. Manufacturers test their products under standard conditions, but your installation may face different environments. You must check the current carrying capacity based on your actual site conditions.

Ambient Temperature and Derating

Ambient temperature affects the effective rating of your busbar trunking. If your installation sits in a hot area, the current carrying capacity drops. You must apply a derating factor to adjust for higher temperatures. For example, if the standard rating is 1600A at 35°C, and your site reaches 45°C, you may need to reduce the amperage to 1400A. Always use manufacturer tables for derating values. This step keeps your system safe and prevents overheating.

Tip: Check the temperature in your electrical room or riser shaft before finalizing your design. High temperatures can lower your current rating and affect system reliability.

Allowance for Future Expansion

You should plan for future growth when selecting your current rating. If your facility expects more equipment or higher power demand, choose a busbar trunking system with extra amperage capacity. Many experts recommend adding 20% to your calculated amperage needs. This approach helps you avoid costly upgrades later and keeps your power system flexible.

OEM Examples of Current Ranges (up to 6300 A)

Major OEMs offer a wide range of busbar trunking products to meet different amperage needs. You can see how current ratings compare across manufacturers in the table below:

Manufacturer	Current Rating (A)
GRL	400–4500

You will find that leading brands like ABB, Siemens, Schneider Electric, and Eaton provide systems with current carrying capacity up to 6300A. These products support various applications, from small commercial buildings to large industrial sites.

OEM	Product Range	Key Features
ABB	BD2, BW, LB series	Ratings up to 6300A, modularity, efficiency
Siemens	SIVACON 8PS	Versatility, enhanced fire safety, monitoring
Schneider Electric	Canalis product line	Wide current ratings, flexible installation
Eaton	Power Xpert	Advanced energy monitoring, adaptability

You should match your design to the amperage needs of your project. Always check the manufacturer’s ratings and select a busduct that meets both your current and future requirements.

Step 2 — Verify Short-Circuit Withstand

When you size busbar trunking, you must check that it can handle short circuit conditions. This step protects your system from damage during faults. You need to understand a few key terms and how to match your ratings to the real fault level in your power system.

Key Terms

Icw (short-time RMS withstand)

Icw stands for the short-time RMS withstand current. This value shows how much current the busbar trunking can carry for a short time, usually 1 second, without damage. You use this rating to make sure the system can survive the high amperage that happens during a fault. Always check the manufacturer's data for the correct Icw value.

Ipk (peak withstand current)

Ipk is the peak withstand current. This is the highest current the busbar can handle instantly when a fault occurs. The Ipk value is higher than Icw because the first surge of current is very strong. You must ensure your busbar trunking can handle this peak without bending or breaking.

Tip: Always check both Icw and Ipk when you review current carrying capacity for protection from short circuits.

Conditional Short-Circuit Rating with SCPDs

You can use short-circuit protective devices (SCPDs) like fuses or circuit breakers to help your busbar trunking meet higher short-circuit ratings. To do this, you must follow strict rules:

• Make sure the cross-sectional size of the busbars and connections matches or exceeds the reference design.

• Keep enough spacing between busbars and connections.

• Use SCPDs that have the same make and performance as the reference.

• Check that the short-circuit rating of each circuit does not go over the reference design.

• Confirm that busbar supports and enclosure design are correct.

• Limit the length of unprotected live conductors.

• Use the same conductor material and properties as the reference.

If you follow these steps, you can safely use SCPDs to boost your system’s short-circuit withstand.

How to Match Busbar Ratings to System Fault Levels

You must match your busbar trunking ratings to the highest fault level expected in your system. Start by calculating the maximum fault current at each point. Then, check that your busbar’s Icw and Ipk ratings are equal to or higher than this value. Review busbar clearance requirements, including phase-to-phase and phase-to-ground distances, to prevent short circuits. Make sure the arrangement and support spacing keep the busbars stable during high current events. Design all connections and bends for safety and reliability. In special applications, like EV charging stations, add extra protection as needed.

Note: Never ignore derating factors for temperature or environment. These can lower your current carrying capacity and affect your system’s ability to handle faults.

Step 3 — Check Voltage Drop

Using OEM mV/A/m Data

You can quickly estimate voltage drop in busbar trunking by using the manufacturer’s data. Most OEMs provide tables that show the voltage drop per ampere per meter (mV/A/m) for each busbar size. You just multiply this value by the current and the total length of your run. This method gives you a fast way to check if your design meets the voltage requirements. Always use the data from the specific product you plan to install, because different materials and designs can change the results.

Tip: If you use copper busbars, you will usually see lower voltage drop values compared to aluminum. Always check the OEM catalog for the exact numbers.

Formula Approach (IEC 60364)

You can also calculate voltage drop using the IEC 60364 standard. This method uses a formula that considers resistance, reactance, current, and length. The main formula is:

• u = k × √3 × (R × cosϕ + X × sinϕ) × IB × L

Where:

• u = voltage drop (V)

• R = resistance (Ω/m)

• X = reactance (Ω/m)

• IB = current (A)

• L = length (m)

• cosϕ = power factor

• k = load distribution factor

Another way is:

• u = b × K × L × IB × 10⁻⁶

Where:

• b = current distribution factor

• K = unit voltage drop (µV/m/A)

• IB = current (A)

• L = length (m)

These formulas help you get a more accurate result, especially for long runs or critical loads.

Design Targets (3% lighting, 5% others)

You should always check your voltage drop against industry targets. The National Electrical Code recommends these limits:

• Maximum voltage drop for individual circuits: 3%

• Maximum voltage drop for total circuits: 5%

These targets help you keep your lighting and power circuits efficient and reliable. If you stay within these limits, you avoid dim lights, equipment malfunctions, and wasted energy.

Worked Example Calculation

Suppose you have a busbar trunking run that is 50 meters long. The load draws 800A, and the OEM data shows a voltage drop of 0.18 mV/A/m. You can calculate the total voltage drop like this:

• Voltage drop = 0.18 mV × 800 × 50 = 7,200 mV = 7.2 V

If your system voltage is 400V, the percentage voltage drop is:

• (7.2 ÷ 400) × 100 = 1.8%

This value is well below the 3% target for lighting and the 5% target for other loads. Your design meets the recommended standards.

Note: Always check your calculations before finalizing your design. Small errors can lead to big problems in power distribution.

Practical Installation Tips

Jointing and Torque Logs

You need to pay close attention to jointing during installation. Proper jointing ensures safe and reliable connections in your busbar trunking system. Follow these best practices:

1. Insert bolts correctly and keep the right insulating distance.

2. Use the correct length and type of bolt for each joint.

3. Check that washers are present and in the right position.

4. Tighten bolts to the specified torque. Always check the product documentation for the correct value.

5. Look for varnish or markings that show the bolt has reached the correct torque.

6. If you are unsure, count the threads sticking out from the nut and check for washers that look crushed or loose.

Keep a torque log during installation. This record helps you track which joints have been tightened properly. Good records make future maintenance easier and safer.

Tip: Always use a calibrated torque wrench for every joint. This tool helps you avoid loose or over-tightened connections.

Fire Barriers and Penetrations

When your installation passes through fire-rated walls or floors, you must use approved fire barriers. These barriers stop fire and smoke from spreading between building zones. Seal all penetrations with certified materials. Check that the fire rating matches the building’s safety plan. Never leave gaps around the busbar trunking. Inspect seals after installation to confirm they are secure.

Supports and Thermal Expansion

You need to support your busbar trunking at regular intervals. Proper supports prevent sagging and keep the system stable. Follow the manufacturer’s guidelines for support spacing. In long runs, allow for thermal expansion. Use sliding joints or expansion units where needed. This step prevents stress and damage when the system heats up during normal power flow. Check all supports after installation to make sure they are tight and aligned.

Note: Good installation practices protect your system and help it last longer.

Copper vs Aluminum Busbars

Performance Differences

When you compare copper and aluminum busbars, you see clear differences in how they conduct electricity and handle heat. Copper has the highest electrical conductivity at 5.96 × 10⁷ S/m. This means copper busbars carry current more efficiently and lose less energy as heat. Copper also has a thermal conductivity of 401 W/m·K, which helps it release heat quickly. Aluminum, on the other hand, has about 61% of copper's conductivity, at 3.77 × 10⁷ S/m. Its thermal conductivity is 237 W/m·K, so it does not cool down as fast as copper.

Material	Electrical Conductivity (S/m)	Thermal Conductivity (W/m·K)
Copper	5.96 × 10⁷	401
Aluminum	3.77 × 10⁷	237

You get better performance from copper in demanding applications. Copper busbar trunking works well in places where you need high efficiency and low heat buildup. Aluminum still performs well for many uses, but it may need a larger size to carry the same current.

Tip: Choose copper if your system needs the best electrical and thermal performance.

Cost, Weight, and Application Scenarios

You will notice big differences in cost and weight between copper and aluminum. Aluminum busbars are lighter and usually cost less than copper. This makes them easier to handle and install. You can use lighter support structures, which saves money on hardware and labor. Aluminum works well in large installations where budget and weight matter most.

• Aluminum busbars are lighter and more affordable, which lowers installation costs.

• The lightweight design means you need less support, saving even more on your project.

• Copper busbars are heavier and cost more, but they give you the best electrical and thermal results.

You should use copper when your power system demands top performance or when space is tight. Aluminum fits well in projects where you want to save on cost and weight, and where the highest conductivity is not required.

Common Mistakes to Avoid

When you work with busbar trunking, you want to avoid common mistakes that can lead to problems during installation or operation. Paying attention to these issues helps you follow guidelines and keeps your power system safe and reliable.

Confusing Breaker Ratings with Busbar Ratings

You might think that the rating of your circuit breaker matches the rating of your busbar trunking. This is not true. The breaker rating shows how much current the breaker can handle, but the busbar rating tells you how much current the busbar can carry safely. If you mix these up, you risk overheating or even a fault in your system. Always check both ratings before you finish your installation.

Tip: Double-check the data sheets for both breakers and busbars. Never assume they have the same current rating.

Ignoring Ambient Derating

Ambient temperature affects your installation more than you might expect. If you ignore derating, your busbar trunking may overheat. High temperatures lower the current-carrying capacity. You must use the correct derating factors from the manufacturer. This step protects your system and ensures safety.

Using Cable Formulas Instead of OEM Data

Some people use cable formulas to size busbar trunking. This can lead to errors. Busbar trunking has different electrical properties than cables. Always use the voltage drop and current data from the OEM. This approach gives you accurate results and keeps your installation within safe limits.

Mismatched SCPDs for Conditional Ratings

Short-circuit protection devices (SCPDs) must match the busbar trunking system. If you use the wrong SCPD, your installation may not handle a short-circuit event. This mistake can damage your power system and put safety at risk. Always follow the manufacturer’s guidelines for SCPD selection.

Remember: Careful planning and correct installation prevent most problems. Review every step to keep your system safe and reliable.

FAQs

What standard applies to LV busbar trunking?

You should follow IEC 61439-6 when you design or install low-voltage busbar trunking. This standard covers all the main requirements for construction, testing, and safety. It also works together with IEC 61439-1, which sets the general rules for low-voltage switchgear and controlgear assemblies. By following these standards, you make sure your system meets international safety and performance guidelines.

Always check the latest edition of these standards before starting your project. This helps you stay compliant and avoid costly mistakes.

How do I size tap-offs?

To size tap-offs, you need to look at the load that each tap-off will serve. First, list all the equipment or devices that will connect to the tap-off. Add up their total current. Then, select a tap-off unit with a current rating equal to or greater than this value. You should also consider the type of protection needed, such as fuses or circuit breakers. Make sure the tap-off matches the main busbar trunking system for both mechanical and electrical compatibility.

• Example: If your tap-off serves a group of machines with a total current of 120A, choose a tap-off with at least a 125A current rating.

What current ranges are available?

Manufacturers offer a wide range of current ratings for busbar trunking systems. You can find products that start as low as 40A and go up to 6300A or more. This range lets you use busbar trunking in small commercial buildings or large industrial plants. Always select a system that matches your calculated load and allows for future expansion.

Application Type	Typical Current Range
Small Commercial	40A – 400A
Medium Industrial	400A – 1600A
Large Industrial	1600A – 6300A

Can busbar trunking be used outdoors?

You can use busbar trunking outdoors if you select products with the right protection. Look for systems with high IP ratings, such as IP65, to guard against dust and water. Outdoor installations may also need extra protection from sunlight, temperature changes, and corrosion. Always follow the manufacturer’s recommendations for outdoor use. Proper installation ensures safe and reliable power distribution in any environment.

Conclusion & CTA

Key Takeaways

You have learned the essential steps for sizing busbar trunking in your electrical projects. Correct sizing protects your system from overheating and keeps voltage drop within safe limits. You must always check the current rating, short-circuit withstand, and voltage drop for every installation. When you follow these steps, you improve both safety and efficiency.

Here are some important actions to remember:

1. Apply strict quality control during manufacturing to keep aluminum busbars reliable.

2. Review all installation details, including the use of strong components like aluminum pipes and round rods for stable power distribution.

3. Inspect and maintain your busbars often to spot problems early and extend their service life.

You should always use the right installation methods to avoid voltage drop and keep voltage levels steady. Regular checks help you catch issues before they affect your power system.

Remember: Careful planning and proper installation keep your system safe and efficient.

Need Help Sizing? Contact Us

If you need help with busbar trunking sizing or have questions about voltage drop, Delixi Electric can support you. Our team offers expert advice on installation, voltage management, and power distribution. We provide solutions that meet strict safety standards and help you avoid common mistakes.

You can reach us by phone at +86 13587807973 or email at dlx@delixi-sh.com. For more information about our products and services, visit Delixi Electric’s official website. Let us help you achieve a safe and reliable installation for your next project.

You can size busbar trunking correctly by following three steps. First, select the right current rating for your installation. Next, check the short-circuit withstand to protect your power system. Finally, calculate the voltage drop to keep voltage stable. Use a checklist for every installation. High-quality products from DELIXI help you meet safety standards. If you have questions about installation, contact DELIXI for expert support.

FAQ

What standard applies to busbar trunking?

You should follow IEC 61439-6 for busbar trunking systems. This standard covers construction, testing, and safety. It helps you ensure your installation meets international requirements.

How do you size tap-offs for a busbar trunking system?

List all devices that will connect to the tap-off. Add their current needs. Choose a tap-off with a rating equal to or higher than this total. Always check compatibility with your main system.

What current ranges can you find for busbar trunking?

Manufacturers offer a wide range of current ratings. You can find products from 40A up to 6300A. This range lets you use busbar trunking in small offices or large industrial sites.

Can you use busbar trunking outdoors?

Yes, you can use busbar trunking outdoors. Select products with high IP ratings, like IP65. These ratings protect against dust and water. Always follow the manufacturer’s guidelines for outdoor use.

Why is voltage drop important in power distribution?

Voltage drop affects how well your equipment works. If voltage drops too much, lights may dim or machines may not run properly. You should always check voltage drop to keep your power system reliable.