What are the safest ways to rack heavy network equipment alone?

Safety comes first. If the equipment is labeled as a two-person lift, ask your manager or site contact to provide a second person rather than improvising. The cost of extra help is much lower than dealing with an injury or damaged equipment. For repeated installs, a dedicated rack lift or equipment lift is worth renting or buying.

There are specialty installation tools and temporary rack supports designed to hold equipment while you fasten it, and they can be useful for solo work. However, light-duty rack studs or ordinary mounting hardware should not be treated as support for a heavy UPS or other large device unless their load rating and the equipment's mounting design explicitly allow it.

A rack lift is the best option when one is available. Many data centers and larger facilities keep one on site, and they are also available to rent. You can position the equipment at the correct height, slide it into place, and avoid trying to hold the entire load while lining up the rails.

Reduce the weight before lifting whenever possible. Remove power supplies, batteries, disks, or other field-removable modules according to the manufacturer's instructions, then reinstall them after the unit is secured. For a heavy UPS or other deep chassis, use a properly rated rack shelf or lift rather than relying on rack screws alone.