Proof load

that tonnage value that a derrick or crane is tested to. The value is equal to the SWL of the derrick/crane + an additional percentage weight allowance, e.g. derricks less than 20-tonne SWL proof load is 25% in excess; derricks 20-50-tonne SWL proof load equals – 5 tonnes in excess of SWL; derricks over 50-tonne SWL proof load equals 10% in excess of SWL.