In answer to the addition question in the comments -
In the case you are describing, the cable should be anchored parallel to the beam. The length of the wire required to limit motion is self-evident from being a straight line - although you should ensure that you have compensated for stretch in the wire, and flex of its mounting under the forces involved.
Then, it's the same method to create a flexible cable that you can use to approximate a possible bent state
Of course, you can get more complicated with it by adding additional construction lines to the style spline:
Which best represents the behaviour of your specific cable is something you will have to test experimentally, really.