The motor on the left is drawn cut open so you can see inside. A real motor is closed.
The nameplate is a 5 horsepower, 208 volt, three-phase motor. Its 16.7 amps is the full-load current for this size in Table 430.250. A real nameplate may read a little different.
3450 rpm is a typical full-load speed for a 2-pole motor this size. The rotor turns slower than the field. That difference is called slip.
The rotor has to turn slower. If it kept up with the field, the field would not sweep past the bars. No current would flow in them, and nothing would pull the rotor.
The stator has six iron teeth, but that does not make six poles. Each winding is a pair of coils on opposite teeth. Together the three windings make one north pole and one south pole, so this motor has 2 poles. Field speed is 120 times 60 cycles, divided by the poles. A 4-pole motor's field turns at 1800 rpm.
A real stator has its windings spread through many slots. The picture shows each winding as one pair of coils.
The colored arrows show each winding's field. The purple arrow is all three added up. It keeps the same size as it turns.
With the rotor still, the field sweeps past the rotor bars 60 times a second. That puts large currents in the bars, and the windings draw large current to match. The bars glow amber when they carry current.
A ring at each end of the rotor joins all the bars. The bars and the two end rings make the cage. The rings are at the ends, so this cut does not show them.
About six times full-load current with the rotor still is typical. Table 430.251(B) lists 102 amps of locked-rotor current for this size.
The current numbers come from a teaching model. It is the standard textbook circuit for one phase of a motor, set to 16.7 amps at 3450 rpm and 100.2 amps with the rotor still.
Starting shows the first moment after the motor is switched on. A motor this size gets up to speed in about a second. The current stays high most of that time, then drops.
Heat in the windings goes up with the square of the current. Six times the current makes 36 times the heat. A stalled motor can burn out its windings in less than a minute.
The red glow shows heat. Real windings this hot do not glow.
A real motor circuit has an overload relay that shuts the motor off when it is jammed. This picture leaves it out.
A single-phase motor cannot make a turning field by itself. It needs a second winding, called the start winding, often with a capacitor.
The graph shows the current at each moment. It peaks 1.414 times higher than the readout.
Amber dots show how much current flows. They do not show electron speed. Real electrons drift less than a millimeter a second.
Black, red, and blue for A, B, and C is common trade practice on 208Y/120. The NEC does not require these colors. The green wire grounds the motor frame.
The conduit is drawn cut open so you can see the wires.
The guard over the coupling is left out of the picture. On the job it is always in place.