USB-C Charging Speed and Data Speed Are Independent - Here's Why That Matters
A USB-C cable can charge at 240W and still transfer data at USB 2.0 speeds - or vice versa. Charging capability and data speed are two separate specs encoded independently in a cable's eMarker chip. Here's how they interact, and why the wrong cable can bottleneck either one.
USB-C promised to be the cable that does everything. One connector, one cable, for power and data. And it delivers on that promise - but only if the cable is built for both. A cable that handles 240W of charging can still limit you to USB 2.0 data speeds. A cable that flies at 10 Gbps might cap your charging at 60W. The reason is that these two capabilities are independently encoded in a cable’s eMarker chip, and cable manufacturers routinely optimise for one while leaving the other at its minimum.
Two specs, one cable
Every USB-C cable that exceeds certain thresholds contains an eMarker chip - a small IC that tells your computer and charger what the cable can handle. The eMarker advertises two categories of information:
Power spec:
- Maximum current (3A or 5A)
- Maximum voltage (up to 20V for SPR / up to 48V for EPR)
- Combined: maximum power (60W, 100W, 140W, 180W, or 240W)
Data spec:
- USB Highest Speed code: USB 2.0 (480 Mbps), USB 3.2 Gen 1 (5 Gbps), Gen 2 (10 Gbps), USB4 Gen 3 (40 Gbps), or USB4 Gen 4 (80 Gbps)
- Whether Thunderbolt / DisplayPort alternate modes are supported
These two sections of the eMarker are completely independent. A cable can declare any combination:
| Cable type | Power rating | Data rating |
|---|---|---|
| Basic USB 2.0 charging cable | 60W (no eMarker) | USB 2.0 (no eMarker) |
| Dedicated charging cable | 240W (5A eMarker) | USB 2.0 only |
| Data-focused USB 3.2 cable | 60W (3A eMarker) | 10 Gbps |
| All-purpose 100W cable | 100W (5A eMarker) | 10 Gbps |
| Thunderbolt 4 cable | 100W (5A eMarker) | 40 Gbps + alt modes |
| Thunderbolt 5 / USB4 v2 cable | 240W (EPR) | 80 Gbps |
The top-right and middle-left cells are the unexpected ones: a cable can be genuinely excellent at charging while being genuinely limited on data - and the other way around.
Why 240W charging cables are often USB 2.0 only
When a cable manufacturer sets out to build a 240W charging cable, the engineering priorities are:
- Insulation and wiring that safely handles 48V × 5A
- An eMarker chip that declares Extended Power Range (EPR) capability
- Compliance with USB PD 3.1 certification
High-speed data wiring is a separate, more demanding requirement. Achieving 10 Gbps or 40 Gbps over a cable requires careful impedance matching, shielded twisted pairs, and sometimes active signal-boosting chips. All of that adds cost and manufacturing complexity that has nothing to do with carrying 48V safely.
So many manufacturers build their 240W cables as power-delivery cables first. The eMarker declares USB 2.0 only for data - not because the manufacturer cut corners, but because the product genuinely isn’t designed for high-speed data. It’s a charging cable that happens to have a USB-C connector at both ends.
The result: you plug your external SSD into your new 240W cable “just to try it,” and your Mac reports a 480 Mbps connection where you expected 10 Gbps.
The other direction: fast-data cables that cap charging
Less commonly discussed but equally real: cables marketed for speed sometimes declare only 3A (60W) for charging.
A USB 3.2 Gen 2 data cable at 10 Gbps needs proper high-speed data conductors. The manufacturer may use thinner insulation, optimise for signal integrity, and not bother engineering the cable for 5A current handling. The eMarker declares 10 Gbps data capability - but only 3A, meaning the cable tops out at 60W charging regardless of your charger’s capability.
Plug this cable between a 100W GaN charger and a MacBook Pro 14" (which supports 96W), and you’ll get 60W. The cable is the ceiling - not the charger, not the Mac.
When you actually need both: Thunderbolt and USB4 cables
The cable types where both high-power and high-speed are standard:
- Thunderbolt 4: 40 Gbps data + 100W charging (5A eMarker, USB 3.2 data speed as fallback)
- Thunderbolt 5: 80 Gbps data + 240W EPR charging
- USB4 Gen 3 with EPR: 40 Gbps + 240W
These are the cables designed from the ground up to do both jobs. They’re also the most expensive - a good Thunderbolt 4 cable runs $25–50, and Thunderbolt 5 cables are currently $50–100+.
How to check what your cable is actually declaring
There’s no external marking that tells you which combination a specific cable uses. The only reliable way is to plug it in and read the negotiated values.
USB Connection Information shows both sides of this on macOS:
- Open a device detail row for a USB 3.x capable device (an external SSD is ideal). The speed field shows the negotiated data rate - if it says High Speed (480 Mbps) for a device that should do more, the cable is declaring USB 2.0.
- For the charger connected at the same time (or the same cable if it’s a dock with charging passthrough), the PD profile list shows the maximum power profile the cable is allowing through.
You can also use this as a deliberate test: connect a known USB 3.x device through the cable and check the negotiated speed. Then check the charger details to see the power profiles. You’ll see exactly which of the two specs your cable is capping.
Practical buying guidance
For charging only (phone, small laptop): Any USB-C cable that fits the wattage. You don’t need USB 3.x data speed in a cable that only touches a charger.
For data only (external SSD, sync): Any USB 3.2 Gen 2 (10 Gbps) or faster cable. You don’t need 240W EPR in a cable that touches an SSD.
For both at once (docking station, laptop + external storage hub): Thunderbolt 4 is the most practical all-rounder: 40 Gbps data, 100W charging, and backward-compatible with everything. If you need above 100W charging through the same cable that carries data, step up to Thunderbolt 5.
Don’t assume a 240W cable does fast data. Read the packaging. “240W” on the box means nothing about data speed. Look for an explicit data speed rating alongside the wattage. If the box only shows wattage, assume USB 2.0 data.
The takeaway
The USB-C connector is the same on every cable, but the wire inside doesn’t have to do everything. Charging capability and data speed are two separately specified, separately engineered, and separately declared capabilities - and the eMarker chip in your cable is advertising whichever combination the manufacturer chose to build. A 240W cable that declares USB 2.0 isn’t broken; it’s a charging cable. A 10 Gbps cable that declares 3A isn’t broken; it’s a data cable. Understanding the distinction saves a lot of confusing troubleshooting.
USB Connection Information shows the live negotiated result for both the power and data sides of every connection - so you can see in one glance whether a cable is the bottleneck, and which spec it’s limiting.
Related guides
- USB-C cables with and without eMarker chips
- Why Are Some USB-C Cables Limited to 100W? EPR and USB PD 3.1 Explained
- Why is my device connecting at USB 2.0 speed?
- How to check USB-C cable speed
- Thunderbolt 4 vs USB4: Identifying Your Connection Type
For real-time visibility into other kinds of connections your Mac makes, see the rest of the Connection Information suite - audio, displays, and network.