Horsepower-hour
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Horsepower-hour
Horsepower-hour
Unit ofEnergy
Symbolhp?h
Conversions
SI units2.685 MJ
CGS units
English Engineering Units

A horsepower-hour (symbol: hp?h) is an outdated unit of energy, not used in the International System of Units. The unit represents an amount of work a horse is supposed capable of delivering during an hour (1 horsepower integrated over a time interval of an hour). Based on differences in the definition of what constitutes the "power of a horse", a horsepower-hour differs slightly from the German "Pferdestärkenstunde" (PSh):

1.014 PSh = 1 hp?h = 1,980,000 lbf?ft = 0.7457 kW?h.
1 PSh = 0.73549875 kW?h = 2647.7955 kJ (exactly by definition)

The horsepower-hour is still used in the railroad industry when sharing motive power (locomotives). For example, if Railroad A borrows a 2,500 horsepower locomotive from Railroad B and operates it for twelve hours, Railroad A owes a debt of (2,500 hp × 12 h) = 30,000 hp?h. Railroad A may repay the debt by loaning Railroad B a 3,000 horsepower locomotive for ten hours.[1]

## References

1. ^ "Archived copy". Archived from the original on 2008-12-04. Retrieved .CS1 maint: archived copy as title (link)