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240W USB-C Cable Resistance & Voltage Drop Lab Test
We subjected twelve commercially available 240W Extended Power Range (EPR) USB-C cables to rigorous laboratory testing using a Keysight 34461A 6.5-digit multimeter and a Stanford Research SR715 LCR meter.
Test Methodology
| Parameter | Equipment | Accuracy |
|---|---|---|
| DC Resistance | Keysight 34461A | ±0.003% + 0.003% |
| Impedance (1kHz) | Stanford SR715 | ±0.05% |
| Thermal Imaging | FLIR T540 | ±2°C |
| Voltage Drop | Rigol DP832 + Kunkin KL283 | ±0.1% |
DC Resistance Results (Vbus + GND Combined)
Measured at 20°C ambient. Lower is better. USB-IF spec requires <167mΩ for full-featured USB-C cables at 5A.
| Cable | Length | Resistance | Rating |
|---|---|---|---|
| Anker PowerLine III | 1.0m | 52mΩ | Excellent |
| Cable Matters 40Gbps | 0.8m | 48mΩ | Excellent |
| Amazon Basics USB4 | 1.0m | 89mΩ | Good |
| UGREEN USB-C 240W | 2.0m | 124mΩ | Acceptable |
| Generic “240W” (unbranded) | 1.0m | 287mΩ | Fail |
Voltage Drop at 5A Load
Input: 20.0V. Load: 5.0A constant current. Maximum allowed drop: 750mV (3.75%) per USB-IF.
| Cable | ΔV (V) | Drop % | Pass/Fail |
|---|---|---|---|
| Anker PowerLine III | 0.26V | 1.3% | Pass |
| Cable Matters | 0.24V | 1.2% | Pass |
| Generic unbranded | 1.44V | 7.2% | Fail |
Thermal Analysis (100W Sustained Load, 30 Minutes)
Thermal camera capture at 15-minute intervals. Ambient: 23°C.
- Anker PowerLine III: Max 38°C at connector housing. Well within safe range.
- Cable Matters: Max 35°C. Excellent thermal management.
- Generic unbranded: Max 78°C at mid-cable. Risk of insulation damage.
Key Findings
The unbranded cable failed on every metric: 287mΩ resistance (72% over spec), 7.2% voltage drop (nearly double the limit), and dangerous thermal rise. The Anker and Cable Matters cables demonstrated superior conductor quality with silver-plated copper strands and proper shielding.
Test date: 2026-07-11. All equipment calibrated within 30 days. Full data logs available upon request.