tension cable backup plan?

[Aaron Harris]

My 30' came with a 3/16" (+ vinyl) 4000lb

tension cable

.

A snow load can weight 10s of thousands of pounds..

Not only do I notice that some 30' manufacturers supply 1/4" 7000lb cable, but I'd like to hang some stuff (bed? 1/2 a loft? potentially a basement access trap door foolishly built to weight 600 lbs?) from a 12' hoop I'll attach to all the rafters.

It seems prudent, since the cable is a single point of failure, to add a backup, so I bought enough 1/4 cable to string the cable around through a new set of holes just inside the snow load studs.

Is this a terrible idea?

Does anyone here understand the math behind calculating the tension on the cable given all the mechanical advantages?

Thank you,
AH