User blog comment:Sanguinior/power weapons/@comment-25451195-20140927060908

It depends on their methods of powering... in some pictures you will see a cable linking the weapon to the armor, powering the weapon via a battery back pack, or the armor it self (in case of Space Marines)

In an IG novel that involved Vostran's on an Ice planet dealing with Orks and Rebels, An IG command squad used had to replace the batteries of their power swords as they were forcing them straight through armor plating on a vehicle to release the locking bolts on the back door of the Chimera.

In all reality though it would be smarter to use a battery system then have cables, as cables can get cut, hung up on something. (hence why a good modern sling for a rifle will have a method to release the weapon from ones person)