We've just re-wired our Sales Office using Cat 6 cabling into a new data rack. The cable loops down at the base, in case we need to use that slack in the future to re-terminate it, or to cover any other eventuality. This spare cable currently sits at the bottom of the rack.
In our old data rack, we have a rack mounted APC UPS. It's proximity to our Cat 5e cabling has never concerned us before, but since we've gone to the cost and hassle of installing new cabling throughout, we're making a concerted effort to ensure that we keep electrical interference to a minimum.
If we move our UPS into our new data rack and sit our UTP Cat 6 directly on top of it, could it cause electrical/magnetic interference or is there some sort of shelf that we should install to maintain a minimum separation? Or is it advisable to keep UPS's out of data racks?
So long as the UPS has it's manufacturer recommended:
you should be fine (assuming the equipment isn't horribly defective). I have 100'+ runs of Cat5e along 220v line, sitting up against the back of the UPS (cabling enters the cabinet at the bottom, where the UPS sits). Never had any sort of issues with any of it.
On a side note, I hope you mean Cat6a, as Cat6 is no faster than Cat5e (1Gbps). Cat6a can do 10Gbps.
I would avoid sitting loops of unshielded Cat6 right on top of a powerful AC current. It's not going to completely kill the signal, but it's not going to do you any favors, particularly if you need to get at or above 1Gbps throughput.