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Using the wrong USB-C cable can damage your tech. Here's how to avoid that

This is a minefield, but these tips will help you get the best cable for you.

Okay, here's what you need to know up front: 

  • When in doubt, use the cable and charger that came with the device.
  • Buy good quality cables from name brands such as Anker.
  • If any cable starts to get overly warm or displays any issues, stop using it!

USB-C seems to have become the default for both charging and data transfer. And that's with good reason -- USB-C is very versatile, currently allowing for power transfer up to 100W and data speeds of 10Gbps.

But the biggest confusion for the end user is that, well, every USB-C cable looks like any other USB-C cable, and every USB-C port looks like any other USB-C port. 

But not all ports and cables are made the same.

For example, your smartphone might come with a 20W USB-C charger and a cable that's good for that load.

But what happens if you connect that cable to something like Apple's monster 140W USB-C charger? Or some random 100W USB-C charger that you bought?

And then you use that cable to connect your laptop to that big power supply.

This is where USB-C gets messy.

The problem is that the complexity of the versatility of USB-C is hidden behind ports and cables that all look the same to the average buyer.

It's a bit like HDMI. It's hard to know what cable you actually need.

But unlike HDMI, it's a lot more difficult to buy USB-C that can handle everything.

This is where E-Mark was supposed to help.

What is E-Mark?

E-Mark is short for Electronically Marked and is actually a protocol controller and the idea was that USB-C cables could be electronically tagged with their power rating and data transfer rates.

Some cables could carry 100W and handle 10Gbps, while others might be limited to 60W and 5Gbps or even 480Mbps.

The idea is to stop 100W of power from being pushed down a cable that can't handle it. This could, at worse, result in fires.

One problem with E-Mark is that it's not as widely supported as it should be. While a quality charger shouldn't try to push 60W or even 100W down an unsuitable cable, I've seen it happen.

And unless you're aware of it, you'd have no idea that it was unsafe.

Then there's the issue of cables that claim to have the E-Mark which do not have the E-Mark. Unless you have a tool that can read the E-Mark, you have to take the manufacturer's word for it.

This is one such tool, the AVHzY C3 USB-C tester. This tool is easy to use -- just supply it power through one USB-C port, and connect the cable you want to test to the other port and it'll tell you if the cable has a chip.

Here is the C3 tester identifying a cable with an appropriate E-Mark chip:

This cable contains the appropriate E-March chip.

This cable contains the appropriate E-March chip.

Here's another:

A USB 3.2 Gen 2 cable containing an E-Mark chip.

A USB 3.2 Gen 2 cable containing an E-Mark chip.

This cable falsely claimed to have an E-Mark chip.

This cable falsely claimed to have an E-Mark chip.

This cable falsely claimed to have an E-Mark chip.

Another way you can tell is if you have a power bank that has a meter that shows volts and amps outputted and can output 100W, along with a device that you know can draw 100W -- such as a laptop -- you can plug the power bank to the laptop using the cable and watch the power draw.

If it draws 20V at around 5A, that's 100W. 

This cable is carrying 100W.

This cable is carrying 100W.

If it's 20V at around 3A, that's 60W.

This cable that doesn't have an E-Mark chip is limited to 60W.

This cable that doesn't have an E-Mark chip is limited to 60W.

Finally, a MacBook will tell you how much power is going into it. Click on the Apple icon on the top-left of the screen, then on About This Mac. From there click on System Report… and then click on Power in the left-hand menu.

macOS System Report showing charging power.

macOS System Report showing charging power.

Wait, so it's possible to cause damage using the wrong cable?

In an ideal world, no. USB-C devices have safety features built into them that that should prevent this from happening.

However, I've seen things go wrong, maybe because a device was defective, maybe it was poor quality to begin with, or maybe something went wrong in the logic somewhere and something crashed. But things can go wrong, and the results can be ugly:

  • Overheating cables
  • Overheating devices
  • Possible battery damage from overcharging (this is rare since most batteries have separate charge controllers, but cheaper devices might not)
  • Risk of fire from overheating or overcharging

Sure, these are edge cases, but do you want an edge case like this happening on your bedside table? I don't.

This is why I prefer to play it safe and use either the cables and chargers that come with a device, or buy high-quality cables that I know are up to the job.

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