A Three Phase Motor Control System
Voltages can range from 200 volts to 575 volts.
Using the highest voltage available will lower the cost of the Motor Starter and require a smaller raceway and wire to the motor.
The motor's nameplate displays the horsepower and voltage(s) it is intended to run on.
Also displayed on this nameplate are the amperages for each voltage.
Select a motor that matches the voltage and hertz frequency (HZ) of the available power source.
The motor and controller must be suited for the environment according to the National Electrical Code (NEC).
The Motor Starter must be sized to the motor.
The National Electrical Manufacturers Association (NEMA) has specific setup standards. Motor Starters are sized according to these standards.
Voltage and Horsepower determine Starter acceptability.
Below is a motor starter selection chart. Find the voltage listed in the top row then move down that column to the horsepower rating of the motor. Follow this rating to the left to determine the NEMA Size code.
| NEMA Size | Ampere Rating | 200 Volt | 230 Volt | 50HZ 380/415 Volt | 480/575 |
|---|---|---|---|---|---|
| 00 | 9 Amps | 1-1/2HP | 1-1/2HP | 2HP | 2HP |
| 0 | 18 Amps | 3HP | 3HP | 5HP | 5HP |
| 1 | 27 Amps | 7-1/2HP | 7-1/2HP | 10HP | 10HP |
| 2 | 45 Amps | 10HP | 15HP | 25HP | 25HP |
| 3 | 90 Amps | 25HP | 30HP | 50HP | 50HP |
| 4 | 135 Amps | 40HP | 50HP | 75HP | 100HP |
| 5 | 270 Amps | 75HP | 100HP | 150HP | 200HP |
| 6 | 540 Amps | 150HP | 200HP | 300HP | 400HP |
| 7 | 810 Amps | 300HP | 600HP | 600HP | |
| 8 | 1215 Amps | 450HP | 900HP | 900HP | |
| 9 | 2250 Amps | 800HP | 1600HP | 1600HP |
Motor Starters do more than just start and stop the motor.
They also protect the motor from damage and minimize the risk of fire.
A properly installed Motor Starter will interrupt the power to a motor if excessive loading is encountered.
The Motor Starter will trip an overload relay if the current to the motor is excessive. It will also remove power from all conductors to the motor.
The supplied voltage to the system may cause a problem. It's not uncommon to lose one of the three phases. This means that the motor is still running on single phase, however, the load that was evenly distributed over all three phases may increase by 150% or more (depending on the loading of the motor).
The overload relay will detect this condition and interrupt power to the motor.
There are many types of overload relays available. The most common are thermal heater overloads which must be installed to match the amperage displayed on the motor's nameplate.
Adjustable overload relays must be within the range displayed on the motor's nameplate. This value must be set. When selecting a motor starter you must know the following;
1) Motor Horsepower.
2) Voltage supplied to the motor.
3) Motor service factor. (Needed when selecting thermal heater overloads).
4) The Starter Housing.
(NEMA) has setup standards for motor starter enclosures which are available in a wide range from indoor general purpose to explosion proof.
Refer to the NEC when making a selection.
Manual motor starters have the same type of overload protection with no control wiring.
One disadvantage is the motor will run until someone turns it off. This is fine for some but not all applications.
Another disadvantage is the motor can be run from a single location only.
If a manual starter is used to run a sump pump the water level will have to be monitored to determine when to turn the pump on and off.
A magnetic starter can be controlled by a float switch.
NEMA Motor starters are available in a wide variety...
Non reversing, Reversing, Multi-Speed, Soft Start and Variable Speed Solid State.