480/240 volt conflict

[Greg Wrenn]

This might be small potatoes for this forum but I thought I would ask anyway. I am moving a machine over to a different plant for our company. I am pretty sure the machine was hooked up to a 240 volt bus bar at the original plant. Now it will be hooked up to a 480 volt bus bar. The conflict that I am seeing is that the motor appears to be already wired up for high voltage, 9 lead lines, 3 load lines divided out to 2 wires a piece under 6 different connectors. However there is a step down transformer inside the control panel for the machine, powering the coils and a receptacle, that has jumpers in place for a 240/120 system. The wires are hookup straight out of the motor control starter so it gets its power from the same place as the motor, so now I am trying to figure out if I have been missing something. As far as I can tell the motor would have been running on 240 volt power while it has been wired up for 480

 

[retirede]

Did you look for a diagram on the motor nameplate?
The high voltage connection for a nine lead motor would normally only have one lead connected to each phase.

 

[Jraef]

Notwithstanding retirede's advice to double check the connections, yes it is possible that the motor has been connected wrong the entire time. What happens then is that because the power is still 60Hz, the motor SPEED is relatively normal, but the TORQUE is half of what it should be and the PEAK torque, used to recover from a change in load, is 1/4 of what it should be. But if the load on the machine is really low compared to the motor size and the load never changes, it may have gone unnoticed for all this time. So for example if it is a mixer that was originally designed for one process needing 10HP, but was repurposed for another than only needed 3HP, that 10HP motor was only putting out the torque of a 5HP motor but that was more than enough so nobody ever noticed. I've seen it happen more than once.

 

[Greg Wrenn]

Notwithstanding retirede's advice to double check the connections, yes it is possible that the motor has been connected wrong the entire time. What happens then is that because the power is still 60Hz, the motor SPEED is relatively normal, but the TORQUE is half of what it should be and the PEAK torque, used to recover from a change in load, is 1/4 of what it should be. But if the load on the machine is really low compared to the motor size and the load never changes, it may have gone unnoticed for all this time. So for example if it is a mixer that was originally designed for one process needing 10HP, but was repurposed for another than only needed 3HP, that 10HP motor was only putting out the torque of a 5HP motor but that was more than enough so nobody ever noticed. I've seen it happen more than once.

Thank you, this makes sense. It is a threader machine so it probably did not have to have much torque to thread the parts. I did change the jumpers on the step-down transformer so that it is now 480/120 and everything else seems to be fine. They have not tested it yet but when I turned it on to check for rotation it did not sound any different than the other threaders that we have and voltage tested good, so it should be ok.