Copper Busbar Ampacity
What Is Ampacity?
Ampacity is the maximum current (in Amperes) a copper busbar can carry continuously without exceeding its maximum operating temperature. Think of it as the "traffic capacity" of your electrical highway. Exceed it, and the copper heats up – potentially melting insulation, loosening connections, or starting a fire.
What Does IACS Conductivity Mean?
IACS (International Annealed Copper Standard) is a benchmark for electrical conductivity. Pure annealed copper is defined as 100% IACS. Higher IACS means less energy loss as heat.
C11000, C10200, C10100: 100% IACS (100% conductivity)
C12200: 85-95% IACS (5-15% lower conductivity)
For the same size busbar, a 100% IACS grade carries more current than a 85% IACS grade.
Key Assumptions for All Ampacity Tables in This Guide
| Parameter | Value |
|---|---|
| Ambient temperature | 35°C (95°F) |
| Maximum busbar temperature | 65°C (149°F) |
| Frequency | 50/60 Hz AC |
| Installation | Bare copper in open air (ventilated) |
| Orientation | Flat (vertical mounting, horizontal busbar) |
C11000 Copper Busbar Ampacity
C11000 copper busbar (100% IACS) is the standard for most electrical applications. Use these ampacity values for C11000, C10200, and C10100 – they are identical.
C11000 Flat Copper Busbar Ampacity (35°C Ambient, 65°C Max Temp)
| Width (mm) | Thickness (mm) | Cross-section (mm²) | Ampacity (Amps) |
|---|---|---|---|
| 20 | 3 | 60 | 180 A |
| 20 | 5 | 100 | 250 A |
| 20 | 6 | 120 | 290 A |
| 25 | 3 | 75 | 220 A |
| 25 | 5 | 125 | 300 A |
| 25 | 6 | 150 | 350 A |
| 30 | 5 | 150 | 370 A |
| 30 | 6 | 180 | 410 A |
| 30 | 10 | 300 | 600 A |
| 40 | 5 | 200 | 460 A |
| 40 | 6 | 240 | 520 A |
| 40 | 10 | 400 | 780 A |
| 50 | 5 | 250 | 550 A |
| 50 | 6 | 300 | 620 A |
| 50 | 10 | 500 | 950 A |
| 60 | 6 | 360 | 720 A |
| 60 | 10 | 600 | 1050 A |
| 60 | 15 | 900 | 1400 A |
| 80 | 6 | 480 | 900 A |
| 80 | 10 | 800 | 1350 A |
| 80 | 15 | 1200 | 1800 A |
| 100 | 10 | 1000 | 1600 A |
| 100 | 15 | 1500 | 2150 A |
| 100 | 20 | 2000 | 2650 A |
| 120 | 10 | 1200 | 1850 A |
| 120 | 15 | 1800 | 2500 A |
| 120 | 20 | 2400 | 3100 A |
A 50mm wide x 6mm thick copper busbar carries 620 Amps under standard conditions. If your load is 500 Amps, this size works with margin. If your load is 700 Amps, you need to go up to 60mm x 10mm (1050 Amps).
For a complete list of standard sizes and specifications, visit our C11000 copper busbar product page.
Ampacity for Thicker Busbars (15mm – 30mm)
For high-current applications, use these values:
| Width (mm) | Thickness (mm) | Cross-section (mm²) | Ampacity (Amps) |
|---|---|---|---|
| 60 | 20 | 1200 | 1750 A |
| 80 | 20 | 1600 | 2250 A |
| 100 | 25 | 2500 | 3100 A |
| 100 | 30 | 3000 | 3600 A |
| 120 | 25 | 3000 | 3600 A |
| 120 | 30 | 3600 | 4200 A |
Get Your Free Busbar Sizing Recommendation
C10100 and C10200 Copper Busbar Ampacity
| Grade | Conductivity | Ampacity vs C11000 | When to Use |
|---|---|---|---|
| C10100 (OFE) | 100-101% IACS | Same | High vacuum, extreme cryogenic |
| C10200 (OF) | 100% IACS | Same | Oxygen-free required, budget conscious |
You do not need to change your busbar size when switching from C11000 to C10200 or C10100. The ampacity is identical.
C12200 Copper Busbar Ampacity
C12200 copper busbar has 85-95% IACS conductivity – about 10-15% lower than C11000. This means for the same physical size, C12200 carries less current.
C12200 Copper Busbar Ampacity (35°C Ambient, 85% IACS)
| Width (mm) | Thickness (mm) | C11000 Ampacity | C12200 Ampacity (approx) |
|---|---|---|---|
| 50 | 5 | 550 A | 470-495 A |
| 50 | 6 | 620 A | 530-560 A |
| 60 | 10 | 1050 A | 890-945 A |
| 80 | 10 | 1350 A | 1150-1215 A |
| 100 | 10 | 1600 A | 1360-1440 A |
How to Size C12200 to Match C11000 Ampacity
To achieve the same ampacity with C12200 as C11000, increase cross-section by 10-15%. This typically means going up one standard size.
Example: You need 620 Amps.
C11000 solution: 50mm x 6mm (620A)
C12200 solution: Use 60mm x 6mm (720A) or 50mm x 8mm (custom)
5 Key Factors That Affect Copper Busbar Ampacity
Ambient Temperature
Higher ambient temperatures reduce ampacity. For every 10°C above 35°C, reduce ampacity by about 12%.
| Ambient Temperature | Correction Factor |
|---|---|
| 35°C (95°F) | 1.00 (baseline) |
| 40°C (104°F) | 0.95 |
| 45°C (113°F) | 0.88 |
| 50°C (122°F) | 0.82 |
| 55°C (131°F) | 0.76 |
| 60°C (140°F) | 0.71 |
Ventilation (Enclosed vs Open Air)
Busbars in enclosed panels or switchgear run hotter than those in open air because heat cannot escape.
| Installation Type | Correction Factor |
|---|---|
| Open air (ventilated) | 1.00 (baseline) |
| Enclosed panel (poor ventilation) | 0.85 - 0.90 |
| Sealed enclosure (no ventilation) | 0.75 - 0.80 |
Multiple Busbars Side by Side (Proximity Effect)
When busbars are placed close together, they heat each other – especially with AC current (proximity effect).
| Number of Bars | Center-to-Center Spacing | Correction Factor |
|---|---|---|
| 1 bar | N/A | 1.00 |
| 2 bars | Same as bar width | 0.85 |
| 2 bars | 2x bar width | 0.92 |
| 3 bars | Same as bar width | 0.75 |
| 3 bars | 2x bar width | 0.85 |
Surface Finish (Bare vs Plated vs Insulated)
Bare copper and tin-plated copper have similar ampacity. Silver-plated is slightly better. Insulation reduces ampacity.
| Surface Finish | Effect on Ampacity |
|---|---|
| Bare copper | Baseline (1.00) |
| Tin-plated | Same as bare (tin is thin and conductive) |
| Silver-plated | +2-5% (lower contact resistance, but bulk heating similar) |
| Heat shrink tubing | -10 to -15% (insulation traps heat) |
| Epoxy coating | -15 to -20% (thicker insulation) |
Altitude
At high altitudes, thinner air provides less cooling. Above 2000 meters (6500 feet), reduce ampacity.
| Altitude | Correction Factor |
|---|---|
| 0 – 1000 m | 1.00 |
| 1000 – 2000 m | 0.98 |
| 2000 – 3000 m | 0.95 |
| 3000 – 4000 m | 0.92 |
Copper Busbar Sizing Formulas
For DC Applications
Cross-section (mm²) ≈ Current (Amps) ÷ 1.5
Example: 500A DC load → 500 ÷ 1.5 = 333 mm² → nearest standard: 50mm x 7mm (350mm²)
For AC Applications (50/60 Hz)
Cross-section (mm²) ≈ Current (Amps) ÷ 1.8
Example: 500A AC load → 500 ÷ 1.8 = 278 mm² → nearest standard: 50mm x 6mm (300mm²)
Rule of Thumb (Memorize This)
| Busbar Size | Approximate Ampacity |
|---|---|
| 20 x 5 mm | 250 A |
| 25 x 5 mm | 300 A |
| 30 x 5 mm | 370 A |
| 40 x 5 mm | 460 A |
| 50 x 5 mm | 550 A |
| 50 x 6 mm | 620 A |
| 60 x 10 mm | 1050 A |
| 80 x 10 mm | 1350 A |
| 100 x 10 mm | 1600 A |
Custom Copper Busbar Sizes
Standard vs Custom Sizes
| Parameter | Standard Sizes (Stock) | Custom Sizes (Made to Order) |
|---|---|---|
| Width | 20, 25, 30, 40, 50, 60, 80, 100, 120 mm | 10 – 250 mm (any) |
| Thickness | 3, 5, 6, 10, 15, 20 mm | 3 – 30 mm (any) |
| Length | 2000, 4000 mm | Up to 6000 mm (any) |
| MOQ | 10 pieces | 50 pieces |
Thickness vs Width – Which Affects Ampacity More?
For the same cross-sectional area, a wider, thinner busbar carries slightly more current than a narrower, thicker one because it has more surface area for heat dissipation.
Example (both 600mm² cross-section):
60mm x 10mm = 1050A
50mm x 12mm = approximately 980A (custom size)
Custom Shape Busbars (L-Shape, Z-Shape, U-Shape)
Bent busbars have the same ampacity as straight busbars of the same cross-section – as long as the bend radius meets minimum requirements (2x thickness for C11000). Tight bends can create localized heating.
For L-shape, Z-shape, or U-shape busbars, the cross-section at the bend is what matters. Use the same sizing rules.
How We Verify Copper Busbar Ampacity and Conductivity
| Test | Equipment | Standard | Acceptance Criteria |
|---|---|---|---|
| Conductivity | Eddy current sigmascope (Foerster) | ASTM E1004 | C11000/C10200/C10100: ≥100% IACS; C12200: ≥85% IACS |
| Temperature rise | Thermocouple array + data logger | IEC 61439 | ΔT ≤ 65°C at rated current |
| Dimensions | CMM (Hexagon) + digital calipers | ASTM B187 | Width/thickness ±0.1mm; length ±0.5mm |
| Resistivity | Micro-ohmmeter (4-wire Kelvin method) | ASTM B193 | Matches IACS calculation |
Precision Dimensional Control for Copper Busbars
Our Manufacturing Equipment
| Equipment | Capability | Tolerance |
|---|---|---|
| CNC shearing machine | Cut to length up to 6000mm | ±0.5mm |
| CNC punching press (AMADA) | Hole punching for mounting | ±0.1mm diameter, ±0.2mm position |
| CNC press brake (ACCURL) | Bending (L, Z, U shapes) | ±1° angle, ±0.5mm position |
| CMM inspection (Hexagon) | Full dimensional verification | ±0.01mm for critical features |
Size Availability
| Parameter | Minimum | Maximum |
|---|---|---|
| Thickness | 3 mm | 30 mm |
| Width | 10 mm | 250 mm |
| Length | 100 mm | 6000 mm |
Protecting Your Copper Busbars During Shipping
| Layer | Material | Purpose |
|---|---|---|
| Inner wrap | VCI (vapor corrosion inhibitor) film | Prevents oxidation during sea freight |
| Interleaving | Foam sheet or kraft paper | Prevents scratching between bars |
| Bundling | Steel straps with edge protectors | Secures bundles for lifting |
| Pallet | Heat-treated plywood (IPPC certified) | Base for forklift transport |
| Outer wrap | Heavy-duty stretch wrap + corner guards | Protects pallet during handling |
FAQ
Q1: How many amps can a 50mm x 5mm copper busbar carry?
A 50mm x 5mm C11000 copper busbar carries 550 Amps at 35°C ambient in open air. At 50°C ambient, it carries 451 Amps (550 × 0.82). For C12200 (85% IACS), the same size carries approximately 470 Amps at 35°C. Always apply correction factors for your specific installation conditions.
Q2: What is the ampacity derating for 50°C ambient temperature?
For 50°C ambient, multiply baseline ampacity by 0.82. For example, a 620A busbar at 35°C is rated 508A at 50°C. This is a standard derating used by IEC and NEC guidelines. Do not skip this step for installations in warm climates, near heat-generating equipment, or in unventilated buildings.
Q3: Does busbar thickness or width affect ampacity more?
Width affects ampacity more than thickness for the same cross-sectional area. A wider, thinner busbar (e.g., 60mm x 5mm) has more surface area for heat dissipation than a narrower, thicker busbar (e.g., 30mm x 10mm) with the same cross-section. Choose width first, then thickness, when space allows.
Q4: How much larger does C12200 busbar need to be to match C11000 ampacity?
Increase cross-section by 10-15% when using C12200 instead of C11000. For a 50mm x 6mm C11000 (620A), use 60mm x 6mm C12200 (720A baseline) or 50mm x 7mm custom. Formula: C12200 cross-section = C11000 cross-section ÷ 0.85. This compensates for C12200's 85-95% IACS conductivity.
Q5: Does tin plating affect copper busbar ampacity?
Tin plating has no significant effect on ampacity. The tin layer is very thin (3-8 microns) and highly conductive. For most applications, you can use the same ampacity values as bare copper. However, heat shrink tubing or epoxy coating reduces ampacity by 10-20% because insulation traps heat.
Q6: How do you calculate ampacity for multiple busbars side by side?
For two busbars placed side by side with spacing equal to bar width, use a correction factor of 0.85. For three bars, use 0.75. For AC applications, the reduction is greater than for DC due to proximity effect. If spacing is increased to 2x bar width, the factor improves to 0.92 (two bars) or 0.85 (three bars).
Q7: Does bending a copper busbar reduce its ampacity?
No – a properly bent busbar has the same ampacity as a straight busbar of the same cross-section. However, if the bend radius is too tight (below 2x thickness for C11000), localized heating can occur. Follow minimum bend radius guidelines: 2x thickness for bars ≤6mm, 2.5-3x thickness for thicker bars.
Q8: Is there an ampacity difference between AC and DC for copper busbars?
Yes, but small. DC ampacity is approximately 5-8% higher than AC for the same busbar size. This is because AC experiences skin effect and proximity effect, which concentrate current on the surface and increase effective resistance. For most applications, using the AC ampacity table for DC is safe (slightly conservative).
Q9: Can you manufacture non-standard copper busbar sizes?
Yes – we manufacture custom copper busbar sizes with width from 10mm to 250mm and thickness from 3mm to 30mm. MOQ for custom sizes is 50 pieces per size. Standard sizes (20, 25, 30, 40, 50, 60, 80, 100, 120mm width) are available from stock with MOQ 10 pieces. Send your drawing for a quote.
Q10: Do you provide certified ampacity test reports for your copper busbars?
Yes – every shipment includes a mill test certificate showing conductivity (%IACS). For large projects, we can provide temperature rise test reports from our lab. We can also arrange third-party witnessed testing by SGS, BV, or other agencies at your request. This is common for switchgear manufacturers requiring certified data.
Q11: How do I calculate busbar size based on load current?
For DC: cross-section (mm²) ≈ Amps ÷ 1.5. For AC: cross-section (mm²) ≈ Amps ÷ 1.8. Then select the nearest standard size from the ampacity table and apply correction factors for temperature, ventilation, and multiple bars. Example: 400A AC → 400 ÷ 1.8 = 222mm² → nearest standard: 40mm x 6mm (240mm², 520A baseline).
