Quick answer: The USB-C plug is standardised; the cable behind it is not. A charge-only lead has four wires and moves 480 Mbit/s with no power delivery negotiation. A full-featured lead adds the SuperSpeed pairs, an e-marker chip and support for up to 100 W or 240 W with EPR. Between them sit 5 Gbit/s, 10 Gbit/s, 20 Gbit/s and 40 Gbit/s variants that look identical. The e-marker reports what the cable can do, and it is the only reliable way to know before plugging in.
Retail packaging helps only a little, because many cables are sold by connector rather than by capability. The practical consequence is a drawer full of identical-looking leads where two work for a monitor, one works for a fast SSD and the rest only charge a phone slowly.
One connector, several cable classes
Charge-only leads
The minimum implementation wires VBUS, ground and the USB 2.0 pair. It charges at up to 3 A at 5 V if the source allows it, moves data at 480 Mbit/s, and has no e-marker because there is nothing to declare. These are the cables given away with inexpensive accessories.
Full-featured leads
A full-featured cable adds all four SuperSpeed pairs, the sideband pins for Alt Mode, and an e-marker that reports current rating, data rate and whether the cable is optically isolated. Without that chip a cable cannot legally carry more than 3 A, which is why a 100 W charger with a non-compliant lead still charges at 60 W or less.
What each class delivers
| Class | Data | Power | Video |
|---|
| Charge-only, USB 2.0 | 480 Mbit/s | 5 V, 3 A, 15 W | No |
| USB 3.2 Gen 1 | 5 Gbit/s | 60 W with e-marker | Alt Mode capable |
| USB 3.2 Gen 2 | 10 Gbit/s | 100 W, 20 V 5 A | Alt Mode capable |
| USB4 Gen 3 | 40 Gbit/s | 100 W | DisplayPort tunnelled |
| USB4 with EPR | 40 or 80 Gbit/s | 240 W, 48 V 5 A | Two displays possible |
The naming, decoded
USB 3.2 is three different speeds
USB 3.2 Gen 1 is 5 Gbit/s, Gen 2 is 10 Gbit/s and Gen 2×2 is 20 Gbit/s over two lanes. Marketing sometimes drops the generation and prints only “USB 3.2”, which tells you nothing. USB4 is clearer: 20 and 40 Gbit/s are mandatory tiers, and 80 Gbit/s appears with the newer specification on certified hardware.
Thunderbolt is a different guarantee
A Thunderbolt 3 or 4 cable is a USB-C cable with additional certification: 40 Gbit/s, PCIe tunnelling and at least 100 W. It works in plain USB-C ports at whatever rate those ports support. Paying for Thunderbolt only makes sense when the devices on both ends use the extra capability.
How to tell what you are holding
Look for printed markings: a 5 A or 100 W rating implies an e-marker, and “USB 3.2 Gen 2” or “40 Gbps” implies the SuperSpeed pairs. Physically, full-featured cables are thicker and less flexible. Software is more reliable than either: a USB analyser or the operating system’s port details will report the negotiated speed and current, which is what actually matters.
Buy by function and label the cable. A Type-C hub will only deliver what the host lead supports, and a USB-C extension cable re-negotiates the e-marker, which can silently reduce 100 W to 60 W. Where a monitor is involved, the cable also needs Alt Mode, and the USB-C to HDMI cable page explains which combinations actually carry video.
Cable care and the marks that matter
A USB-C cable fails at the ends, not in the middle: the plug shell takes the bending load and the solder joints inside it crack. Pull the plug, not the lead. Keep cables away from radiator heat and from the sharp edge of a desk, and coil them loosely rather than wrapping them around a charger. Printed markings such as 5A, 100W, 10Gbps or 40Gbps are worth photographing when the cable is new, because they rub off within a year and are the only external clue to what the cable can do.
Heat is the other slow failure. A cable left on a dashboard or behind a radiator softens its jacket and stresses the solder joints at the plug, and the fault appears months later as an intermittent connection that only shows up when the cable is warm. Keep spare cables coiled loosely in a bag rather than in a pocket, and do not use a charging cable to lift a phone off a table; the plug shell is not designed as a handle.
Practical scenarios
- Laptop charger at 100 W: the bundled lead matters as much as the brick; a charge-only cable caps the laptop at 15 W and shows a slow-charging warning.
- External NVMe enclosure: use a 10 or 20 Gbit/s lead; a charge-only cable makes the drive run at hard-disk speed and look faulty.
- Desk with one cable for everything: choose a USB4 or Thunderbolt certified lead, because it must carry video, data and power simultaneously.
- Vehicle or travel kit: keep two labelled leads, one charge-only and one full-featured, so a slow charge in a car park is not a mystery.
FAQ
Are all USB-C cables the same?
No. They share a connector and a minimum behaviour for charging at low current. Data rate, power ceiling and video support vary widely, and the e-marker is what declares the difference. Two cables that look identical can differ by a factor of twenty in throughput.
Does a USB-C cable support video automatically?
No. Video needs the SuperSpeed pairs wired for Alt Mode, the host must support DisplayPort Alt Mode, and the cable must be full-featured. A charge-only cable carries no video at all, which is why a monitor stays dark with one lead and works with another.
What is an e-marker and do I need one?
It is a small chip in the cable plug that reports the cable’s current rating and data capability. You need one for anything above 3 A or above USB 2.0 speeds. Cables sold for 100 W or 240 W always have one; cheap charge leads do not.
