ED's is a percentage measure of the connection time. This pullmagnet is specified for 100% ED. This means that it can be switched on continuously without overheating. Note that the product can not be stuck in the pull position for too long, but the stroke must go all the way into the hold coil. If this happens (the solenoid gets stuck in the pull coil for too long) it will overheat and damage the coil. This can happen if the weight the solenoid is trying to pull is too heavy or if it is not supplied with a sufficiently high current (Amp).
The specified holding force applies in ideal conditions without a safety factor.