The rule that creates the two classes
USB-C cables are built for either 3A or 5A. At the PD ceiling of 20V, that is 60W or 100W. To protect hardware, the system will not push more than 60W through a cable unless the cable identifies itself as 5A-capable via an e-Marker chip embedded in the plug. Consequence for buyers: a 100W charger bundled with a 60W cable delivers 60W, and the customer blames the charger. The blog version of this failure is USB-C cable wattage.
Matching cable class to program
- Chargers to 65W: 60W-class cables suffice electrically for single-port use at 20V/3A; 65W models that publish 20V/3.25A need the 5A class to reach their top step - check the profile, not the headline.
- 100W chargers: 5A e-Marker cables, non-negotiable. The 100W series publishes 20V/5A; only an e-Marker cable unlocks it.
- Wireless kits: the documented cable in the manufacturer's wireless line is 1 m at 3A - the station's ceiling is 15W, so the 60W class is ample and correct.
Verification
An e-Marker can be read with inexpensive USB testers; build the check into incoming inspection for 100W programs. Also verify the cable at full load for voltage drop - thin conductors in a long cable sag below spec long before they fail outright. Full specification language is in the USB-C cable guide.