Do i need to connect both usb cables?

I have a transcend 1 TB external drive (usb 2); It has two usb cables but also works if i connect the thicker one. Do i need to connect both for it to work properly or prevent damage or something?

3 Answers

It's safer using both, since Harddisk may consume more Power on spin up, as USB is designed for.

Fourthly, many consumers and computer users buy 2.5” hard disk drives as portable storage devices inside USB chassis. A lot of chassis like that have no additional power supply, while a single USB connector can provide maximum 500mA current. So, some hard drives requiring a lot of power may face serious stability problems or may not be recognized by the system at all.

More information provided here

USB-Specs

From the wikipedia article.

Some devices, such as high-speed external disk drives, require more than 500 mA of current and therefore may have power issues if powered from just one USB 2.0 port: erratic function, failure to function, or overloading/damaging the port. Such devices may come with an external power source or a Y-shaped cable that has two USB connectors (one for power+data, the other for power only) to be plugged into a computer. With such a cable, a device can draw power from two USB ports simultaneously.

The required currents are rarely documented but should normally be written on the drive.
E.g. all Seagate drives up to 500GB I've seen indicate +5V .45A and work on a single USB port.
But 750GB and 1TB drives show .75A or .90A and don't.
The current is maximum at spinup.
So, I suppose that a frequent .55A is OK on a single USB port as long as the drive starts.
if you're unable to read the drive label, you can do

$ lsblk -do NAME,MODEL
NAME MODEL
sda ST9750420AS

and look for that drive on eBay to read the current in its label.
Unfortunately

$ lsusb -d 14cd:6116 -v
Bus 001 Device 127: ID 14cd:6116 Super Top M6116 SATA Bridge Self Powered MaxPower 2mA

obviously indicate only the case requirement.