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Why is three phase power used and why should I buy three phase machinery?

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Three-phase machinery is typically cheaper than single-phase machinery of the same power rating as it can be more easily located on the used machinery market through adverts, at auctions or from machinery refurbishment specialists. The reason for this is that historically single-phase machinery has only been of low power and so there is, as yet, little stock of ex-industrial high power single-phase machinery in circulation.

This situation is unlikely to change much in the short or medium term as most industrial machinery continues to be manufactured using three-phase motors. Unless exotic designs and/or materials are used it is simply not cost-effective to manufacture compact high power single-phase machinery.

Single-phase motors of less than 1hp or so are readily available whereas motors of greater than 3hp (2.2 kW) are seldom single phase. Moreover, the poor starting torque characteristics of single-phase motors and their increased cost are such that if a machine has a primary three-phase motor in it - and therefore can be assured of having three phase power available - then it is quite likely that the designers of the machine will have installed three-phase motors in even the smallest drives.