View Full Version : electrical supply to machinary

03-29-2002, 07:47 AM
could someone please explain how 3 phase power works. what is the difference to single phase? what is the optimum setup for the average workshop?

03-29-2002, 08:53 AM
On of the other members posted this site awhile ago and it is a good source for the answers to that question. Check it out and if you still have questions bring them back to us.


I'd like to give proper credit but I can't remember who first posted this link


03-29-2002, 09:09 AM
Let me approach it this way ..Take a pencil and draw three lines on a sheet of paper...label them A,B&C these would be the 3 wires of a 3 phase distribution system to a motor. The voltage potential between wires A&B,A&C and B&C are all 480volts in a 3 phase 480 volt system.These three wires all connect to the windings in the motor as an example assume the 3 motor windings to be all connected to each other in a trianglar pattern, the 3 points of the triangle are labeled A,B&C this is where the 3 corresponding wires connect.

For a single phase 220 volt motor draw 2 lines and label them 1&2, the voltage potential betweem 1&2 is 220 volts.

For a single phase 120 volt draw 2 lines and label them 3 and 4 ,4 will be the neutral and 3 will be the hot leg.The voltage potential between 3 & 4 is 120 volts.

Now draw 2 coils of wire on a piece of paper( these will be the windings of a dual wound 120/240 volt motor) Label the ends of the wire of the coils 1&2 for the first coil and 3&4 for the other.

Now connect the coils together by connecting coil ends 1&3 to wire 3 of the 120 volt system above and connecting coil ends 2&4 to wire 4 of the 120volt system above you now have the motor connected for the 120 volt operation.

Now start over with the two independent coils and connect the coil ends together in this fashion connect coil ends 2 & 3 together and then connect wire 1 of the 220 volt system above to coil end 1 and wire 2 of the 220 volt system above to coil end 4 you now have the motor connected for the 220 volt operation.

If you will take a couple of minutes to draw this out you can see how all this makes sense.If I have explained it properly .

The home work shop is normally setup with 120/240 users while commercial shops will usually use 3 phase systems of varing voltages.

The advantages of higher voltages and 3 phase systems is when the motor is run in a continious duty mode it will run cooler as the current is essentially halved when the voltage is doubled in the 120/240 system. The current is also lower in the 3 phase systems, this all supports a longer life span of a motor. The breakaway torque is also higher as the voltage increases giving you faster starts and responce to loading up of the motor.

A properly manufactured, well maintained and not abused motor will have a 15 to 20 year life expectancy.

Sorry if it got to be a long one but I don't believe I could have been any more brief.

good cutting ...dick

03-29-2002, 09:15 AM
I think it was Lou


03-30-2002, 03:32 AM
yes, it was me. Google is a wonderful thing. Put three phase electrical into the google search window and pushed the button. Got lots of links the one above was the best at making something that would take me 3 pages to explane into a one page simple explanation.