USB cables, like all cables, have a recommended length, with anything over that edging into unsupported territory. That can lead to a connection that’s spotty, or encounters errors when you try to transfer data, or it may not recognize the connected device or accessory at all. But why is that? Just as Ethernet cables that are too long, or HDMI cables that don’t adhere to their specifications, the signal just gets too weak to be adequately picked up at the other end.
The actual maximum length of a USB cable is dependent on a number of different factors, not least the quality of the cable itself. But the generation of USB you’re looking to utilize, and even the connector type, will constrain both its maximum length and its potential performance.
Fortunately, if you come up against the maximum length of your USB cable and wish it could be longer, you do have some options to get around it. You could opt for a generation of USB cable that has a longer maximum length, you could switch to an active USB cable, or you could extend its length with a USB extender.
So if you’re looking to run some USB cables and want to make sure you stay within the guidelines for USB maximum cable length (or how best to break them) read on. Here’s everything you need to know about how long a USB cable can actually be, and how to make the most of it.
Most USB cables are duplex in design, which means that they communicate both ways, even when conducting a data transfer from one device to another. When a USB cable sends a packet of data, it waits for a response from the other end before sending the next packet. The longer a cable is, the longer time it takes for that signal to travel down the cable, and the greater chance there is of “late collision” errors. For cables that go beyond the recommended specification length, there’s an even greater chance of these sorts of errors.
USB cables that are too long also run the risk of attenuation, due to natural resistance in the wiring, the strength of the signal transmitted down a length of USB cable will gradually diminish the further it is transmitted. In USB cables that don’t exceed the maximum rated length, that shouldn’t be a problem, as the signal will still maintain enough strength by the time it reaches the end for the information to be effectively received. However, in cables that do exceed the maximum length, especially if they’re built to a lower quality with sub-standard materials, that can lead to a signal being received incomplete, or not at all. That’s also true of higher data rate cables from newer generation USB devices, with faster data rates leaving less time for the packet response (which is why newer USB cables tend to have shorter maximum lengths).
The end result can be choppy video, if that’s what you’re transmitting, or a corrupted file transfer, or simply the data not being received at all.
There is also a much greater risk of interference from outside sources in longer cables – particularly if they’re longer than official specifications suggest, or made of lower-quality materials.
That’s not to say that it’s impossible to go longer than the typical maximum lengths of USB cables. You just need to know how to do it. Read the sections below for more information on how to run really long USB cables.
The maximum recommended cable length for USB 2.0, is five meters, or around 16 feet. That’s actually the longest maximum length of any standard, passive USB cable specification, with USB 1.0 cables restricted to just three meters.
You may find some USB 2.0 cables that run longer than 5m, but they’ll need to be made with a thick wire gauge to ward off signal loss and interference at anything much past that maximum. Alternatively, you can run longer USB 2.0 connections by bridging two USB 2.0 cables with a powered USB hub.