Harrison 15" 190 Electrical Question

[Homebody]

I have a Harrison 190 that I am just starting up. The main contactor was burned up when I got it. I replace it with the same contactor that was there before. The contactor is normally open. The contactor is energized at all times and of course hums a little. Im new to motor controls and electrical work of this kind so I am questioning if the lathe has somethinig wired wrong. I can see that at one time there was a contactor with a different foot print. I also see now that I think that the contactor is too small as it is labeled as 3 HP at 230 volts. My machine has a two speed rated at 3HP and 7.5 HP. It is rated at 25 amps and the motor full load amps is 21.6, so I am not understanding that variation either. Isnt it unusual for a machine to sit there and use electricity around the clock if it isnt being used? The only way to make it stop is to turn off the main disconnect. I have not been able to locate a schematic so if anyone has one to share I would greatly appreciate it. I have been able to find manuals but no schematics.
Thanks

 

[John Rudd]

Homebody,

Where do you live? UK or USA....

Normally a contactor used to fire up a motor has some sort of control circuitry associated with it..in my experience..

I'd be inclined to determine why the contactor failed in the first instance...What has failed? the contacts themselves or the coil?

 

[Homebody]

Hi John
Sorry it took so long to get back. Life came up. I live in the US. The coil failed. Thanks for responding!

 

[rkepler]

On a lot of industrial size equipment there's a main power contactor and a disconnect. The disconnect interrupts power to the contactor and the contactor is closed with a momentary switch somewhere on the equipment.

A 3HP contactor will burn its contacts if you're switching 7.5HP through it, but since the rating is for the contacts and not for the coil the motor size isn't related to the earlier failure. It sounds like the original failed for some reason and was replaced with one lower rated than the motor size. You should be OK with the one you have as long as you leave the motor on the 3HP setting.

In sum: yes, the disconnect is the "normal" way to power off the lathe and the coil will hum, loudly if the mount is not great.