You do not really understand something unless you can explain it to your grandmother. -Albert Einstein-
"This post is intended to be a very general, all purpose primer, one that even Gramma can understand,"
Many ... questions reveal most ordinary people have not a clue about electricity, and the difference between single phase and three phase power. They think voltage is something done in dark corners and is illegal in Mississippi. This shall attempt to explain it all to you, with some tedious details omitted for clarity and sanity purposes.
Visualize this now if you will...
Principle 1: Electricity is now tiny peas.
They are hard to see because they are so small and move so fast, however, they are green. ( OK, you guys at Argonne National Labs - prove I'm wrong!)
Principle 2:The number of peas is measured in amps.
There are so many in a kilo, but it is inconvenient to weigh them.
Principle 3: The speed of the peas is measured in volts.
This can be converted to miles per hour, or furlongs per fortnight if so desired, but volts are nice and tidy.
So the power the peas have is the number of peas multiplied by their speed.
This is just how hard the peas hit.
Same principle as getting hit with a water hose.
Secondary Idea 1 for Principal 4: Two peas going one speed does the same work as one pea going twice as fast.
( 2 x 1 = 1 x 2)
Secondary Idea 2 for Principal 4: Electrical power is measured in watts
What is Watts?
Watts = Amps x Volts
Principle 5: The more peas you cram in a pipe, (amps in a wire), the more they rub against the walls.
This is resistance and it is measured in ohms.
Secondary Idea1 for Principal 5: You can get more electrical work from the same size pipe (wire) if fewer peas going faster are used so there is less rubbing (resistance).
Secondary Idea 2 for Principal 5: Rubbing on the pipe (resistance) results in heat. Heat deteriorates insulation.
Volts, Amps and Ohms are related.
A pack of peas will cram itself into a pipe until the resistance to movement they create by rubbing uses up all their available speed.
Number of Peas= Speed / Resistance, or Amps = Volts divided by Ohms. (I=E/R)
This is known as Ohms Law and is the basis of all electronics.
Use this information to amaze your friends.
You now understand electricity. That's all there is to it.
Get yourself a tool belt, a bad attitude and a wiggy, and you can be an electrician.
Be sure to mumble things about potential differentials or power factor and you can pass as an electrical engineer.
( Please don't ask what a wiggy is. There are some things one could get hurt for divulging.) Okay, okay, I'll tell, the venerable Wiggy® Voltage Tester has been on the market since 1918.
An electric motor is a machine to get useful work from electricity. It is also two magnets chasing each other, with one magnet tied to a rotating shaft, while the power company changes their polarity just when the north and south poles start to line up.
Some people think motors run on smoke because when the smoke gets out, they stop working. This is not true.
There is a practical problem with the magnets in that if they happen to line up north to south on startup, they will stay that way. The reasons for this are too boring to go into and involve things like induced rotor currents and slip. Read on for the exciting conclusion.
Motors can run on AC (alternating current) or DC ( direct current).
Some can run on both.
AC motors are the most generally used and that is all this is going to deal with. [ My web post - my rules
C. PHASE AND MOTORS AND ENERGY
The changing of polarity in the magnets is caused by a change from positive to negative in the power supply.
( AC = Alternating current)
In the USA, thanks to the clock lobby, this happens 60 times per second.
One cycle from zero through positive and negative and back to zero on one set of wires is called a phase.
(Not technically correct but it helps to make some sense out of this).
Motors frequently are wound to run on one or more than one phase.
In the USA, single phase and three phase are the rule.
Single phase motors
require some mechanics to get around the starting problem.
They use a small start winding attached to a capacitor ( a tank for electrons) which changes the phase of the start winding slightly due to the time it takes the capacitor to fill up.
They also need a relay to cut the start winding out after startup so it doesn't burn up.
Three phase power
has each phase reach zero 120 degrees out from each other. There is no way for the poles to line up exactly so it will always start.
The work (not scientifically accurate) that a motor can do is measured in horsepower.
By definition, this is 550 foot pounds per second. (It is also 745 watts).
One horsepower is one horsepower regardless of phase, voltage, RPMs, manufacturer, or political affiliation. So why care about such things? Money.
All the extra gear a single phase motor needs to ensure starting costs money and it eventually fails so the motors are more expensive and less reliable. There is also a practical size limit of 7.5 H.P. which is where most manufacturers stop making them.
The amps needed to generate a horsepower are spread over three wires in a three phase motor and two wires in a single phase motor so the wires are bigger with the single phase motor.
...If it is a submersible motor you still have to run a third wire for the start winding.
In the USA,
the common combinations of approximate voltage and phase are:
115 Volts Single Phase.
This is house wiring.
It is safer because the voltage is lower and so can push less amps through the resistance of some hapless idiot who takes the hair dryer into the shower.( A True story with a "Short" messy ending).
Single phase is supplied with a single transformer and thus cheap for the power company to supply and thus popular with them. Usually limited to motors of 1 H.P. or less.
230 Volts Single Phase.
Your air conditioner, clothes dryer or electric stove. The main entry power for most new houses.
208 Volts Three Phase.
Power companies like it for subdivisions where street lighting is involved. Motors hate it. Power companies don't care. ( It is a personal problem.)
230 Volts Three Phase,
Common where loads are small, usually less than 40 H.P.
If a transformer neutral ( 4 wire service) is run in, 115 volt single phase can be pulled off from any leg and neutral. Very useful in small industrial and commercial and farm applications.
460 Volts Three Phase,
The common heavy industrial and large pump supply. Carries the most energy with the smallest wires and starters. Comes and gets you if you are careless.
Why does it matter?
1. The voltage and phase available must match the motor you buy or it won't work.
2. The supply wire size and the starter size depend on amps.
For a given size motor, amps depends on voltage. Twice the voltage, half the amps.
A motor rated for two voltages uses the same energy on either. The internal coils are either connected in series or parallel depending on the voltage so it is all the same to the motor.
Adaptation Source:PumpsOnlinedotcom website