What size crane do I need?

The crane size depends less on the weight alone than on the weight at the distance it has to travel. Here is how providers work it out, so you can give them the right numbers.

The five numbers that decide it

1. Load weight, plus the weight of the rigging, hook block and spreader bars. Rigging often adds 500 to 2,000 lb.
2. Radius: the horizontal distance from the crane's center of rotation to where the load is picked and set. Measure to the furthest point.
3. Height: how high the load must go, including clearance over parapets, trees or equipment.
4. Setup space: outriggers on a 50 ton crane spread to about 20 to 25 feet wide.
5. Ground: soft soil, fresh fill, sand or buried utilities may need crane mats.

Worked example

A 6,000 lb rooftop unit sits 55 feet from the nearest spot where a crane can set up. With about 800 lb of rigging, the crane must lift 6,800 lb at 55 feet. At that radius, a 40 ton crane's chart may allow only around 7,000 to 9,000 lb. That is too tight. A 60 ton crane gives a comfortable margin, so expect quotes for the larger crane.

Watch for power lines

Federal rules (OSHA 1926.1408) generally require cranes to stay at least 20 feet from power lines up to 350 kV unless the utility de-energizes them or a specific clearance plan is in place. Point out any overhead lines when you request a quote.

Checklist to send with your request

• Item and weight (nameplate or submittal)
• Distance from setup to pick and set points
• Height needed
• Photos of the setup area, the access route and overhead lines
• Preferred date and time window