Hi Guys....
As it happens, the U.S. utilise a completely different electrical distribution system than that used in Oz, the U.K. etc.... Most of their consumer distribution is achieved with Open Delta transformers via only two phases with three phase distribution limited to commercial/industrial consumption.
Most U.S. households utilise a two phase mains with 220V between phases and 110V between phase and neutral. 220V feed is used for high load devices such as Stoves, Large Clothes Dryers and Ducted Air Conditioning, etc while 110V is limited to Lighting and Small Appliance Power Outlets. This is all due to striking a balance between power consumed (Load Watts) and the size of the conductors required to carry the load current - For the same Load, the current required increases as the Voltage decreases, an inverse proportional relationship.
Most commercial/industrial 3-Phase distribution is at a voltage of 440V, not 220V and at a frequency of 60Hz, not 50Hz as we use here in Oz and most of Europe for example. This is why motor driven devices designed to operate in the U.S. are always quoted as operating at an increased speed of 20% compared to equivalent 50Hz motor driven devices.
Large grinders like the 3-Phase Robur, etc require the extra power and torque offered by a 3-Phase motor which can be accommodated in a smaller frame size and therefore able to be fitted into the shell of a standard sized Robur. A single phase motor of equivalent power and torque will be significantly larger in size and probably wouldnt physically fit - This is due to poorer efficiency and the need to use larger diameter copper conductors in the motor windings, since a single phase motor operates at a much lower voltage and therefore would need to draw much higher current.
So there you go.... A brief explanation without delving into the maths and physics involved

Mal.



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