https://www.irs.gov/pub/irs-pdf/i4562.pdf
Applicable depreciation methods are prescribed for each classification of property as follows. However, you may make an irrevocable election to use the straight-line method for all property within a classification that is placed in service during the tax year. Enter "200 DB" for 200% declining balance, "150 DB for 150%" declining balance, or S/L for straight line.
Note. If you elected to accelerate pre-2006 unused research and minimum tax credits in lieu of special depreciation allowance for eligible property, you must depreciate the basis in the property using the straight line method. Enter "S/L" in this column for the applicable property classification. If you are depreciating other property in the same classification as the property for which this election was made and using a different method, enter "Various".
3-, 5-, 7-, and 10-year property
Generally, the applicable method is the 200% declining balance method, switching to the straight-line method in the first tax year that the straight-line rate exceeds the declining balance rate. However, the straight-line method is the only applicable method for trees and vines bearing fruit or nuts. The 150% declining balance method is the only applicable method for any qualified smart electric meter or any qualified smart electric grid system property placed in service after October 3, 2008.
For 3-, 5-, 7-, or 10-year property eligible for the 200% declining balance method, you may make an irrevocable election to use the 150% declining balance method, switching to the straight-line method in the first tax year that the straight-line rate exceeds the declining balance rate. The election applies to all property within the classification for which it is made and that was placed in service during the tax year. You will not have an AMT adjustment for any property included under this election.
15- and 20-year property (not including qualified leasehold improvement, qualified restaurant property, or qualified retail improvement property) and property used in a farming business- The applicable method is the 150% declining balance method, switching to the straight- line method in the first tax year that the straight-line rate exceeds the declining and balance rate.
Water utility property, residential rental property, nonresidential real property, qualified leasehold improvement property, qualified restaurant property, qualified retail improvement property, or any railroad grading or tunnel bore. The only applicable method is the straight-line method.