Wiring a VFD question

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Bltien

Joined
Feb 1, 2017
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Like a couple of my prior threads, I’m quite ignorant when it comes to electrical stuff.
I’m wiring two 3 phase 2 hp motors to the same KBAC 27 VFD following Ed Caffrey’s tutorial on his website.
https://www.caffreyknives.net/1_vfd_2_motors.html
Ed’s example shows the two motors attached to the toggle switch and a set of wires going from the toggle switch to the U, V, W terminals in the VFD. The current switch for the single motor goes to another spot on the VFD as shown in these pictures.
https://imgur.com/a/XmXvM7G
My questions is if I can just detach the current switch and wires from the VFD, then wire the new switch like in Ed’s tutorial?

It may be a stupid question... but I’m pretty stupid when it comes to this kind of stuff lol.
 
Another question... what needs to be done with the thermostat leads? The new motor has them...
 
I am not exactly sure which switch you want to detach from the VFD. The one in the bottom right is not strictly required, but the Start/Stop one is as I understand it.

I think you want to leave the current switches in the VFD in place. If I were to do this, I would not put the toggle into the VFD but in a separate box, mainly because I have a forward/reverse switch in the VFD. So, I would just run the output that is currently going to your single motor into the toggle, and the two outputs from the toggle to the two separate motors. The toggle just selects which motor is driven, you still need the start switch to turn it on.
 
Leave all the existing switches where they are. They control the VFD functions.
Connect three wires to the U,V,W terminals.
Connect the other end of that wire to the "Device Selector Switch" center terminal.
Connect the two motors to the end terminals of that switch.

In use, switch the device selector switch to the machine you want the VFD to control. THEN, turn on the VFD and run the machine as normal. DO NOT switch the device selector switch while the VFD is ON or RUNNING.
 
Thanks for the help guys. That’s simple enough.

I think my only remaining question is about the thermostat leads on the new motor. Is a thermostat necessary or could I leave them alone?
 
Just in case it is not obvious: make sure you also connect a ground wire to each motor.

The thermostat wires could be used to turn off the VFD in case the motor overheats. Can you post a model number or link to a manual for the motor? It is probably a normally closed switch.

Honestly, I probably would not bother with the thermostat, but that's just me.
 
Hubert S. said:
Just in case it is not obvious: make sure you also connect a ground wire to each motor.

The thermostat wires could be used to turn off the VFD in case the motor overheats. Can you post a model number or link to a manual for the motor? It is probably a normally closed switch.

Honestly, I probably would not bother with the thermostat, but that's just me.
Click to expand...
I have grounds hooked up to each motor. I’ll look for a box for the switch tonight... should there be a place for the ground wires in the switch box?
Regarding the thermostat wires, I can take a picture of the motor when I get home. It’s just for a disc grinder so it won’t have very heavy use.

Edit: I guess I don’t need a separate box for the switch... I think I’ll just put it in one of the spare spots in the VFD.
 
Last edited:
Hubert S. said:
Just in case it is not obvious: make sure you also connect a ground wire to each motor.

The thermostat wires could be used to turn off the VFD in case the motor overheats. Can you post a model number or link to a manual for the motor? It is probably a normally closed switch.

Honestly, I probably would not bother with the thermostat, but that's just me.
Click to expand...
Here’s the motor.
https://imgur.com/a/mgLTTu4
 
If it is a metal box, it needs to be grounded. The newer boxes I've worked with had a green screw for that. If you are looking for dust/waterproof cord grips, I recommend McMaster if you cannot find them locally. They have them for around $3-4 each.

Is the new motor the same HP as the other one? If not, I would call KB before doing this. There are jumpers in the drive that select the motor HP. I am not sure what might happen to the drive or motor if the jumper is not correct for one of the motors. The KB people can probably tell you what to do with the thermostat leads as well. I've called them before and they provided excellent support.

The first two pages of search results did not return a manual for the motor model number for me. I suspect the thermostat is just a regular bi-metal switch that trips when the motor gets too hot and automatically resets when it cools down again. This could be used to shut down the drive by connecting it to the stop terminals on the drive, or you could cut the power to the drive through a separate relay. Maybe K Ken H> will chime in, he seems to know a lot about this kind of stuff.
 
Hubert S. said:
If it is a metal box, it needs to be grounded. The newer boxes I've worked with had a green screw for that. If you are looking for dust/waterproof cord grips, I recommend McMaster if you cannot find them locally. They have them for around $3-4 each.

Is the new motor the same HP as the other one? If not, I would call KB before doing this. There are jumpers in the drive that select the motor HP. I am not sure what might happen to the drive or motor if the jumper is not correct for one of the motors. The KB people can probably tell you what to do with the thermostat leads as well. I've called them before and they provided excellent support.

The first two pages of search results did not return a manual for the motor model number for me. I suspect the thermostat is just a regular bi-metal switch that trips when the motor gets too hot and automatically resets when it cools down again. This could be used to shut down the drive by connecting it to the stop terminals on the drive, or you could cut the power to the drive through a separate relay. Maybe K Ken H> will chime in, he seems to know a lot about this kind of stuff.
Click to expand...
The new motor is the same HP as the first one. They’re both 3 phase 2hp Baldors. I think I will just put the new switch in one of the empty spaces on the VFD instead of a separate box. I think that will be easiest.

I think I just need to figure out what to do with the thermostat leads if I have to do anything. Each has a wire nut on it already. Should they be fine capped like that?
 
Bltien said:
The new motor is the same HP as the first one. They’re both 3 phase 2hp Baldors. I think I will just put the new switch in one of the empty spaces on the VFD instead of a separate box. I think that will be easiest.

I think I just need to figure out what to do with the thermostat leads if I have to do anything. Each has a wire nut on it already. Should they be fine capped like that?
Click to expand...
Leaving the thermostat wires capped with a nut should be fine and the motor will run.

Personally, I would not put the switch in the VFD box for two reasons. I think a forward/reverse switch is really useful, particularly for a disc grinder, so I would not put the toggle in the slot for the forward/reverse switch. The toggle switch looks bulky, not sure if it would fit in the spot in the middle. The second reason is that I would likely switch between the motors by accident, which I assume is not good for the motors or the drive. If you don't intend to use a reverse switch, you could rotate the toggle switch ninety degrees as shown in the website you linked to make it less likely to accidentally flip the wrong switch. I think it is safer to use a separate box that is a bit out of the way to lessen the odds of switching between motors while one of them is running. Just something to consider, either way will work.
 
Hubert S. said:
Leaving the thermostat wires capped with a nut should be fine and the motor will run.

Personally, I would not put the switch in the VFD box for two reasons. I think a forward/reverse switch is really useful, particularly for a disc grinder, so I would not put the toggle in the slot for the forward/reverse switch. The toggle switch looks bulky, not sure if it would fit in the spot in the middle. The second reason is that I would likely switch between the motors by accident, which I assume is not good for the motors or the drive. If you don't intend to use a reverse switch, you could rotate the toggle switch ninety degrees as shown in the website you linked to make it less likely to accidentally flip the wrong switch. I think it is safer to use a separate box that is a bit out of the way to lessen the odds of switching between motors while one of them is running. Just something to consider, either way will work.
Click to expand...
I had thought about those concerns too. After thinking about it more, I think I’ll just add a hole in the bottom left face of the VFD. That would keep it out of the way enough that I wouldn’t flip it by accident and would still let me put in a reverse switch, which I want to do.
 
Well, I've been following this thread and good advice has been given so I'd not chimed in. I like Mr Hubert's idea of putting the selector switch in a separate box. This might help remind to stop a running motor before switching to other motor. Also depends on how much distance is between the two motors using the same VFD, AND how much room is inside the VFD enclosure. I just don't like tight enclosures for wiring power leads.

Ed Caffery's page gives good wiring info with photos, and Stacy provides a couple of good suggestions that should be followed. No need for more info from me on the wiring. On the motor thermostat leads, depending on the motor this could be from an internal RTD or a simple high temp contact closure. I would just tape those up and stick in the motor pecker head and forget about them.

Good luck and have fun.
 
Mount the Device Selector Switch on the box that you run the two motor wires and the U,V,W wires. A simple wall junction box with the switch mounted on the cover is fine. Connect the grounds in the same box.

HINT:
Position the switch so it moves toward the motor that is being energized.
s-l500.jpg
 
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