480 volt three phase motor

[bayy99threeway]

on my job i was ask to wire some motors for a warehouse.for ventaltion 480 three phase half horse power motors were on there on starter with stop start with overloads 0f 1.5 amps there were 8 motors wired in paralell off a 30amp fused disconnect after wiring the motors and starters turned on one at a time they all for ran awhile then shut down one by one four of them burn up and four are still working. what I think happen was the voltage droped out the motor was multi tap everything was good on that. tell me what you think.also did a voltage test when i started the four motors that were left one by one and the voltage continue to drop.

 

[iwire]

A total of 8 three phase 480 volt 1/2 HP motors?

Table 430.250 shows those motors to have a FLA of only 1.1 amps/

The total load would only be 8.8 amps and once you calculate the feeder size you at about 9 amps

(seven @ 1.1 + one @ 1.1 x 1.25%)

9 amps on a single 30 amp disconnect is fine, assuming the conductor sizing is 'normal' I would not expect enough voltage drop to burn up the motors.

Furthermore motors driving fans can really deal with a lot of voltage drop without burning up.

My first thought is that you did not connect the duel voltage motor up correctly. If your sure that is not it then there is another issue to look at.

Take a current reading on each leg of each motor and make sure that each motor is drawing no more then it's labeled FLA on any leg, also see if each leg is drawing equal currents.

If you find that the actual current reading exceeds the motors FLA I would look at slowing the fan down, it is possible someone installed the wrong pulleys on the motor or fan resulting in to much load on the motor.

Most of the pulleys installed on the motors of blowers are adjustable sheave type so that you can adjust the fan speed.

 

[cadpoint]

To me it's not so much that the motors are allowed to be combined its the distance thats between them, maybe ?

The machinist handbook for belts and rotation ratio's, I'm sure you could find a web link as well ...

Well said Iwire!

 

[glene77is]

Are the Overloads (per FLA) protecting the motors during runtime?