What is the longest USB cable I can use with a USB hub?

Let's talk USB cables

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USB cables

Cables...Let's talk USB cables

When you buy a professional USB hub you naturally want to know what your cable options are, you may be fine with a nice short cable to sit the USB hub on your desk, or you might need it several feet/meters away to fit in with your workplace.

In this post we’ll be covering the options you have to make sure you can still data transfer (sync) at the fastest speed, but also use the length of cable that suits your use case scenario.

Standard data transfer USB cables are male to male, meaning they connect the USB hub to the host computer seamlessly.

The length of the USB cable is limited by the USB specifications https://www.usb.org/, meaning if you want the data transfer / sync rate promised by the UBS hub, you need to comply with those specifications and follow these simple rules.   

Cambrionix USB hubs auto-detect attached devices and automatically adjust the current output to the highest level permitted by the device manufacturer and USB specifications USB Battery Charging V1.2.

How about cable limitations?

As with all standards, USB possesses multiple limitations to its design.

This means in practice; the USB specification limits the length of a cable between full speed devices to 5 meters (a little under 16 feet 5 inches). For a low speed device, the limit is 3 meters (9 feet 10 inches)

This looks like this in a diagram, with the maximum hub depth of 5 USB hubs:

USB cable length

Which translates as: 

USB3.x USB setup:
Host >>3m>> USB Hub #1 >>3m>> USB Hub #12>>3m>> USB Hub #3>>3m>> USB Hub #4 >>3m>> USB Hub #5 >>3m>> DEVICE.

USB2.x USB setup: 
Host >>5m>> USB Hub #1 >>5m>> USB Hub #2 >>5m>> USB Hub #3 >>5m>> USB Hub #4 >>5m>> USB Hub #5 >>5m>> DEVICE.

With a regular USB cable the max length is 5 meters for 2.0 and 3 meters for USB 3.0/3.1

Theoretically then if they daisy chain the hubs with max cable length the furthest the last hub could be from the host would be USB 2.0 is 30 meters (about 82 feet) and USB 3.0/3.1 is 18 meters.

What is USB specification?

Charging devices not at their optimum charging level has a number of issues.

According to Wikipedia (https://en.wikipedia.org/wiki/USB) the:

“Universal Serial Bus (USB) is an industry standard that establishes specifications for cables and connectors and protocols for connection, communication and power supply (interfacing) between computers, peripherals and other computers. A broad variety of USB hardware exists, including several different connectors, of which USB-C is the most recent.

Released in 1996, the USB standard is currently maintained by the USB Implementers Forum (USB-IF). There have been four generations of USB specifications: USB 1.x, USB 2.0, USB 3.x and USB4. “

SB-IF Battery Charging Specification revision 1.2 (BC1.2) and the full specification can be found here:  https://usb.org/sites/default/files/USB_Battery_Charging_1.2.pdf

This specification was created to try to unify battery-charging attributes for USB 2.0 in the future. The idea was to minimize the number of cell-phone chargers ending up in landfills, by converging on one USB-charging specification. The European Union has been an early adopter to the notion of less waste. Specifically, they have committed using the same micro USB connectors on data-enabled cell phones, but they have yet to fully adopt the BC1.2 specification.

In the BC 1.2 specification, there is a mode referred to as Charging Downstream Port (CDP) that allows for data and higher charging currents.

If a voltage between 0.4V and 0.8V is sensed on D+ of a host or hub device, then D- should respond with 0.5V to 0.7V.

Once CDP has been established, peripheral devices are allowed to draw up to 1.5A and simultaneously communicate data. 

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USB 3 male-to-male cable

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