I have just released a plugin to create catenary curves.
From Wikipedia:
Catenary is the curve that an idealized hanging chain or cable assumes under its own weight when supported only at its ends in a uniform gravitational field.
It is essentially a "line object" plugin: click and drag to get the initial couple of end points on the XY plane.
Customizable parameters:
Independent Z for both ends.
Direction [downward (chain) or upward(arch)].
By length or by sag methods: you can establish the length of the chain or the chain lowest (or highest) point.
Buttons to extract a 3D polygon or a 2D polygon out of the PIO.
More info on my site page: Catenary Curve for Vectorworks®