You are here:

Electric Motors/air compressor motor


I have a Baldor induststrial motor thermally protected motor  ive tried to look up info on it all i can find is the following:

HERTZ:     60
SPEED [rpm]:     1725
OUTPUT [hp]:     2
PHASE:     1
VOLTAGE:     115/230

I have a 20 amp breaker in the box and 240 ran to it problem is the diagram shows  LINE and shows it connected to line 4 of the motor im assuming both wires go on the same terminal but when i flip the breaker on it doesn’t do anything motor doesn’t hum or anything if i hard wire it without the air compressor pressure switch is sparks in the box and pops breaker  any idea ? and the ground wire is connected to the green screw inside the box on the motor

MIKE,    I am assuming you are bringing two lines to the motor,    should be from a double pole breaker,  so you can bring 230 to the motor.  You actually need to bring three wires,   two hots, [normally blacks]  and one from the ground bus,  with wire rated for the amperage at 220 which I don's see listed here but the nominal for 2HP at 230 volts is 12 amps.

You mention 240,  which could be,  it is whatever the utility supplies and should be 230 plus or minus 10% not  10 volts,  10%   23 volts if the measured voltage is exactly 230,

The connection diagram should show how to connect for 115 or low,  and 230  high voltage.

I have to assume you have followed the diagram and configured the terminal strip or motor lead combinations , in this instance  you mention terminal,  so you would configure the jumpers or move the wires to configure the motor to accept the high voltage option,  and you did that properly.

Now,  LINE  is correct,  for both the low and high connections but there should be TWO terminals that accept incoming line,     one may be hard to read,  sometimes the terminal board slips under the frame a bit and is hard to read,     

You never connect both incoming lines to the same terminal, regardless of voltage,   if you connect the two incoming lines together,  on one terminal you have a direct short,    

Regardless of what the incoming lines are routed through,  pressure switch,  on/off switch  there should still be two lines to the motor,  and line marked to two terminals,     at both voltages,   

The third line should be brought directly from the breaker box to the green screw,   not one of the power lines    either voltage,     

I am thinking you have one hot 220 to one of the line terminals, and one to ground,  which will do exactly what you explained,     

Line to ground should be half the voltage between the two hot HIGH Legs,     which was common with appliances for years,  where the neutral was connected to a terminal and the high legs to two others,  now days the law is four wires,  two 220 hots,  one neutral, and one pure ground leg to the ground terminal,     most all buildings that are wired hard are sometimes grandfathered to just three, in other areas  you must replace the outlet,  to fit the four prong cord on modern appliances,       

So make sure you have the motor wired for high voltage,  if new, it is common but not standard for the new motor to come pre connected for the high side,   this is to prevent a low voltage connected motor from being connected to twice the rated voltage,    so they normally connect it high,  and if it is powered by low voltage,  less chance of any damage to anything,  but do not assume the motor is wired for high or 230,   check it,      

Somewhere there are two LINE TERMINALS,    and one ground    and the ground is just that,  ground,    

A single phase dual voltage reversible motor should have:
T1, T2, T3, T4, T5, and T8.
They are: T1, T2, T3, T4 - Run winding leads;
T5, T8 - Start winding leads.
For 115V operation, the leads should be wired: T1 + T3 - L1 (Line input) T2 + T4 - L2 (Line input) T5 and T8 are wired to L1 and L2 and to reverse the motor, you reverse T5 and T8 in respects to L1 and L2.

For 230V operation, the leads should be wired:
T1 - L1
T4 - L2
T2 + T3 + T5 - (just wire nut these together)
T8 - L1 or L2 (depending on the motor rotation you want).

Above is fairly standard NEMA single phase dual voltage connections,  board or not,   yours may be a single direction motor,  the provided information does not say, but often compressor duty motors are one direction motors,   CW or CCW looking at the shaft,      

but you MUST find the other line terminal and it is NOT THE GROUND SCREW on either voltage,  

Electric Motors

All Answers

Answers by Expert:

Ask Experts




Three phase/ AC DC single phase motors, controls, any problems or failures, motor installation, performance issues, connections. All other electric motors/gearboxes/apparatus. Specialty repair concerns, obsolete motors and solutions. Other mechanical or specialty equipment. See my profile under Home/electrical at this site


30 plus years in the electrical motor and apparatus repair industry. VP level management of repair facilities, current owner of my own specialty repair and consulting firm.

EASA, IBEW [retired], other specialty organizations, Lubrication, Vibration EDI, Tribo-electric Councils

Currently fielding concerns at this site under "Home Electrical"

4 year technical, College level specific courses, EASA repair courses, vibration analysis electronic and electrical trade school.

©2017 All rights reserved.