How to wire a 3 phase motor? There is a wide variety that exists in the manufacturing of three-phase motors that drive heavy industrial loads. It would not be correct to say that one type of motor is superior, otherwise, that’s the only kind of motor that would exist. Instead, we see a few different motor types, often indicated by the wires and the data plate on the side.
How To Wire a 3 Phase Motor?
Three-phase motors are more efficient than single phase motors and are commonly found in applications requiring more than 7.5 horsepower. Although the National Electric Code does not specify specific conductor colors for three-phase current, it is common to use black, red and blue wires to identify lines L1, L2 and L3 respectively.
The voltage cycle of each line lags its predecessor by 120 degrees — L2 reaches its peak voltage after L1, and L3 reaches its peak voltage after L2. Two wiring configurations, Wye and Delta, indicate the wiring methods for three-phase motors. These instructions cover a dual voltage, three-phase motor, the most common type.
Preparation
Step 1
Turn off the power supplying the circuit to be wired to the motor. A three-phase motor must be wired to a three-phase supply.
Step 2
Open the motor wiring box and identify the wires within. The nine wires should be labeled 1 through 9. Some motor leads are identified by color; in this case consult the motor documentation for lead identification.
Step 3
Examine the motor nameplate for wiring information. The nameplate will specify the motor voltages and may give specific wiring information. Many motors can be wired for a high and low voltage and for either Delta or Wye (sometimes called Y or Star wiring). Wire the motor for the appropriate voltage to which you are connecting the motor.
Step 4
Make all wiring connections with wire nuts of the correct size for the conductors being used and the number of conductors being connected together. If there is a neutral wire in the conduit or cable supplying the motor, it is unused for the motor’s three-phase wiring; cap it with a wire nut.
For example, use a red wire nut to connect two 12-gauge wires. Hold the bare ends of the conductors together and twist on a wire nut.
Step 5
Swap any two line connections to reverse the motor rotation. For example, move supply line T1 to T2 and supply line T2 to L1 and the motor will reverse direction. You can buy motor control switches to accomplish this change.
Wye Wiring
Step 1
Make the connections for low voltage, 230-volt wiring. Connect motor leads 4, 5 and 6 together. Connect motor leads 7 and 1 with the black L1 conductor. Connect motor leads 8 and 2 with the red L2 conductor. Connect motor leads 9 and 3 with the blue L3 conductor.
Step 2
Make the connections for high voltage, 460-volt wiring. Connect motor leads 6 and 9 together. Connect motor leads 5 and 8 together. Connect motor leads 4 and 7 together. Connect motor lead 1 to the black L1 conductor. Connect motor lead 2 to the red L2 conductor. Connect motor lead 3 to the blue L3 conductor.
Step 3
Connect the ground wire to the motor’s ground terminal. Loosen the ground terminal screw, insert the ground wire into the terminal and tighten the screw firmly. Close the motor’s wiring box.
Delta Wiring
Step 1
Make the connections for low voltage, 230-volt wiring. Connect motor leads 1, 7 and 6 to the black L1 conductor. Connect motor leads 2, 8 and 4 to the red L2 conductor. Connect motor leads 3, 5 and 9 to the blue L3 conductor.
Step 2
Make the connections for high voltage, 460-volt wiring. Connect motor leads 9 and 6 together. Connect motor leads 4 and 7 together. Connect motor leads 8 and 5 together. Connect motor lead 1 to the black L1 conductor. Connect motor lead 2 to the red L2 conductor. Connect motor lead 3 to the blue L3 conductor.
Step 3
Connect the ground wire to the motor’s ground terminal. Loosen the ground terminal screw, insert the ground wire into the terminal and tighten the screw firmly. Close the motor’s wiring box.
Low Voltage Wiring
When the supply voltage is lower, the total resistance of the load must also be lower in order to generate the same output power. As long as the resistance stays equal, then an equal application of voltage should then also yield an equal output power for each winding.
Since the voltage is squared, doubling that voltage from a low (240) to a high (480) source would require a 4x increase in resistance to maintain an equal output power.
In order to achieve this lower resistance, the ideal configuration would be a parallel network. This is accomplished by creating a second small bonded Wye set of coils in the motor. Both of these small parallel Wye’s will be supplied with an incoming line lead.
Imagine from Line 1 to Line 2. The current may travel from Line, through T7, to T8 back to Line. In parallel, it may travel from Line, through T1, T4, T5, and T2 back to Line. Both parallel paths contain two series windings. The total resistance therefore will be equal to the resistance of 1 winding alone.
For a 240-volt input, each of the windings will drop 120 volts, since there are two windings in series in each path.
High Voltage Wiring
For high voltage, the total resistance must be 4x higher than for low voltage in order to maintain the rated output power.
The original wiring diagram showed the proper arrangement of windings to create a larger Wye system in which there are four equal windings between any two leads.
In this wiring setup, there are 4 windings in series between any two Line leads. Compare this to the low voltage. From Line 1 to Line 2, the current only has one path through T1, T4, T7, T8, T5, and T2 back to Line. This gives a resistance equal to 4x the value of one single winding.
Again, comparing the power to the low voltage, if the input voltage is 480 volts, each of the 4 series windings will drop 120 volts. This is the same voltage, and therefore power, as the low voltage scheme.
FAQs
How do you hook up a 3 phase electric motor?
In the star connection, all the ends of the coil are connected to a coon point and are powered by the other free ends. The delta connection, on the other hand, connects each end of the coil to the beginning of the next phase, allowing the system to be fed through the connection points.
How many wires go to a 3 phase motor?
The most common type of three-phase motor is that which has nine labeled (and often colored) wires coming out of the box on the side. There are many motors with more or fewer wires, but nine is the most common.
Does a 3 phase motor need a neutral?
Three-phase systems may or may not have a neutral wire. A neutral wire allows the three-phase system to use a higher voltage while still supporting lower voltage single-phase appliances. In high voltage distribution situations it is common not to have a neutral wire as the loads can simply be connected between phases.
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