Yes, there is a limit as to how much tension you can place directly on aluminum or copper - as defined by the following equations:

Copper: Tm = 0.008 x n x cm

Aluminum: Tm = 0.006 x n x cm

"Tm" is the maximum allowable tension applied to the cable conductor, "n" is the number of cables, and "cm" is the individual conductor area in circular mils.

You'll have to adjust these equations to reflect the number of cables taking the tension. For example, if you're pulling three single-conductor cables (either cradle or triangular configured), n=2, since two of the cables may sustain the total pulling tension. If you're pulling more than three cables of equal size, the maximum tension you can directly apply to the conductor material is 60% of the total value.