When I torque lugs using Aluminum wire, I will apply, say 50 ft. lbs., then several days later check the torque. It will be down to, say, 35 lbs, so I re-torque it. Other ECs say you should just torque it and forget it--that the loss in tightness is built-in to the required torque. Of course Copper holds its torque so it is not a problem. What do you guys and gals say about this?
Not "another" reason- THE reason! Aluminum is notorious for "creep" when over-torqued. Aluminum should not be torqued to the same values as copper for this reason. Simply put, too much pressure causes the metal to flow, leaving you with a loose connection. Make sure the value you're using is the correct on, and not "something always used."
The following is a very important quote from the document that Nick has posted a link to.
It is often asked whether bolted connections require periodic retightening. The simple answer is NO. Once the connector is installed with the proper torque, repeated tightening could actually damage the connector and/or the conductor and eventually lead to a failure.