VFD question.. wiring

ScottRoush

ScottRoush

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Jan 10, 2010
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I'm getting set up to run both of my 1.5HP, 3 phase motors.. one for KMG, one for disk grinder.. on one VFD. I've been reading all the threads and I've decided to go the route of using a 3PDT on-off-on switch instead of plugs.. mostly because those plugs are bloody expensive. My main question is how to wire the switch to the VFD (KBAC 27-D). I read to use the empty pole between the AC and the Motor banks... but how do I wire it to the switch? What kind of wire? And where on the switch? I know to use the center (off) poles... but there are three. And only one on the VFD.

I would really appreciate any help on this....
 
I'm not sure what you are looking at when you say there is only one on the vfd.
The VFD has 3 terminals for you motor T1 T2 T3. For what I think you are trying to do, connect T1 T2 and T3 to each of the center poles of the switch. Then connect the KMG to the upper poles and the disc to the lower poles. If anything runs backwards Switch any 2 wires on the offending device. Use the same wire you use for hooking up the motors, usually 14 ga or larger.
 
ScottRoush said:
I'm getting set up to run both of my 1.5HP, 3 phase motors.. one for KMG, one for disk grinder.. on one VFD.

I've been reading all the threads and I've decided to go the route of using a 3PDT on-off-on switch instead of plugs.

My main question is how to wire the switch to the VFD (KBAC 27-D).

What kind of wire?
And where on the switch?
Click to expand...

little mac said:
The VFD has 3 terminals for you motor T1 T2 T3.
For what I think you are trying to do, connect T1 T2 and T3 to each of the center poles of the switch.
Then connect the KMG to the upper poles and the disc to the lower poles.

If anything runs backwards Switch any 2 wires on the offending device.
Click to expand...

I agree with that

How about a diagram?
vfdtoswitch2motors-1.jpg


1-9c.jpg


16 gauge 4 wire - stranded wire is good on a 1.5 hp motor, only 5 amps per leg
 
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Okay.. mine isn't labeled T1, T2, T3

It goes thus:

{ U V W } empty terminal { L1 L2 }
Motor AC Line

And a related question.... On the motor 'terminal bank' on the VFD as seen above.. the terminals are labeled U V W. The cable supplied to wire to motor has brown, yellow, red and green. I obviously know where the green goes... but what about the other three?

You are saying the switch wires go then to what I have labeled U V W right??
 
ScottRoush said:
And a related question.... On the motor 'terminal bank' on the VFD as seen above.. the terminals are labeled U V W. The cable supplied to wire to motor has brown, yellow, red and green. I obviously know where the green goes... but what about the other three?

You are saying the switch wires go then to what I have labeled U V W right??
Click to expand...

It doesn't matter into which slot you put the wires. It the unit runs backwards you can switch two of them here or at the motor.
 
Thanks again...

One more question...

Since I'm not ready to connect my disk grinder, can I just wire one motor to the vfd.. and then later put the switch in between the VFD and motors? For example... by cutting the wire coming from the installed motor to the motor terminals in the VFD, wiring the cut wire from the VFD to the center terminals of the switch, and then wiring both motors to the switch? Does that make any sense at all???

Another question... My VFD didn't come with a power switch. It only has the start/stop. Do most people install the power switch or is it fine to just use the start/stop? Although doing it this way leaves the unit on all the time unless it's unplugged.
 
Scott, I understand what you just said. That would work, retro-fitting the switch. Or, if you have the switch now, you could just wire it into the power out from the VFD, hook a motor to one side of the switch, and just leave it selected to that side. When you get another machine ready, just wire it to the other side of the switch, no fuss no muss. Just like the Count drew.

I did wire a master power switch into the power to the VFD. I like being able to totally turn it off, and not use the breaker for a switch. I turn the VFD off if I'll be out of the shop for a few days or if I want to blow dust out.

I used a 20A 3PST on/off switch for that.
 
Thanks Salem....

I tried that first... and I got NO power to the motor at all. The VFD showed everything normal but nothing on the motor. So I took it off and wired the motor directly the VFD and it worked fine.
 
Does anybody have any clue as to why I may not be getting power to the motor when using the 3PDT switch? Other than the switch is bad???

Actually.. It just occurred to me.. I wonder if wired them in the right orientation on the switch? Do the rows run parallel to the direction that the switch moves? Or perpindicular?? I hate electricity.
 
Does anybody have any clue as to why I may not be getting power to the motor when using the 3PDT switch? Other than the switch is bad???

Actually.. It just occurred to me.. I wonder if wired them in the right orientation on the switch? Do the rows run parallel to the direction that the switch moves? Or perpindicular?? I hate electricity.
 
Always meter a switch so you know how it works, and that it works.

The Counts diagram in post 3 would have a switch that toggled left to right.
 
Typically the switch would be ON/OFF/ON

That's how Sam's drawing would work. Usually the switch is rectangular and a motor would go on each short end. The center would be power in.
Like Brian F said. Meter the switch to confirm.
 
Fellhoelter said:
Always meter a switch so you know how it works, and that it works.

The Counts diagram in post 3 would have a switch that toggled left to right.
Click to expand...

Yes

It's easy to meter a switch & eliminates lots of headaches to verify it before you use it.

I had the switch direction in the photo, but it was a pretty shaky drawing. - put it back in for clarity
 
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Thanks a lot folks.

Another thing that I just saw... the switch I bought is rated 3/4 hp. And I have 1.5hp motors. I saw that amps were an issue in all the threads I read.. but never any mention of horse power ratings on the switch. What are the issues with that? Is this switch inappropriate???
 
can you scan and post the paperwork that came with your switch and vfd? Just the prints would be enough information to help you get it working
 
Hi... no paperwork for the switch just a plastic bag.... 15 amp, 3/4HP 3PDT on/off/on

I will try to take a picture of the VFD stuff...

But.. I did have the wrong orientation with my wiring so I'm pretty sure that was the reason.

I need to find out if the HP rating of the switch has to match that of the motor. I'm assuming it does.....
 
Your amperage rating needs to exceed your draw.
And the wider that margin, the better.
15a at, I am guessing, 250v is not the one I would purchase, but I would give it a go if it was what I already had on hand.

I don't think a 1.5hp motor would ever draw 15A
 
Switches that are going to be subjected to high-inrush inductive loads, such as an AC motor, will often be rated in horsepower in addition to volts and amps. This rating reflects the amount of current the switch contacts can handle at the moment the device is turned on. An AC motor will draw up to eight times its running current when first turned on or when held stationary while energized (stalled rotor). The switch in the example below would be rated for use with a 3/4HP motor at 125 through 250 volts AC.

Typical Carling Technologies' switch rating:
10A 250VAC
15A 125VAC
3/4HP 125-250VAC

Here's a copy and pasted explanation since I was having a hard time thinking of a way to say it...


Hope this helps!!
 
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