KBAC VFD Line (ON/OFF) Switch Installation

Installing a Main Power Switch in the KBAC-27D

The KBAC series of VFDs are great little VFDs for anyone who wants to operate a small three phase motor without all the hassle of packaging a less expensive NEMA 1 VFD into an enclosure with a fan and wiring the speed control and all that. The base model KBAC-27D does not come with a main power switch.Without the switch you will be unplugging it when it's not in use. Instead of a power switch it has a rubber plug which seals the hole where the switch is to go. 

You could buy the line switch kit that KB Electronics makes for this purpose, or gather the parts yourself from the hardware store and wire it up like I did. 

NOTE: This information presented here is intended for educational purposes only. It is not intended to replace the advice of a qualified professional electrician. Always exercise extreme caution when working with electricity. All wiring must adhere to national and local electrical codes. 

  • Phillips screwdriver
  • Wire strippers
  • Crimping tool (Crimper)
  • DPDT toggle switch (GSW-15)
  • GB Toggle Switch Cover (1)
  • Blue ring terminal for #6  (about 1/8") stud (4)
  • 14 AWG wire, about  5 ft. (150 cm)
  • Insulated female quick connects, 1/4" (4)
  • Cable ties (5) or electrical tape. 


The idea is that this plug is going to be replaced with a heavy duty toggle switch. Push the plug out from the back. 

Cut the 14 AWG wire into four 16" (40 cm).

Strip about 3/8" (10 mm) of the insulation off and slip the ring lugs on.

Crimp each with about the same force as your crazy uncle's killer handshake and the lug will be stuck.
Give it a pull to see it's stuck good.

With the keyway in the threaded part of the switch body facing you, connect the ring terminals to the bottom four switch terminals. IMPORTANT: The wires with the felt pen marks must go on the same side of the switch either left or right is okay.
Switch wired with the center and bottom terminals used.  The upper two terminals are not used for this application.

Push the switch through the back of the door. The switch will only go in one way as the hole and the switch are keyed. The wires will be coming off the lower half of the switch as shown.

Adjust the nut on the switch so there is about 1/8" (3 mm) of threads sticking through the door face.

Thread on the rubber toggle switch cover and tighten it up.

I attached some cable ties and formed a bend in the wiring. This will allow the bundle to coil up inside the door when the door is closed.

Remove the factory installed jumpers that go between L1A and L1B and L2A and L2B.

Plug the quick connects on ensuring that the two wires with the marks go right two terminals (L1A and L1B).

Apply a couple more cable ties and clip the excess off. You can see the loop is formed to tuck inside the door space.

Visual Inspection

Double check that the wires with the marks on the right side of the switch.
Double check that these same marked wires end up at the VFD circuit board terminals L1A and L1B.
Make sure that no wires are being pinched in the door seal when the door is closed.

Ohmmeter Check

Set power switch to OFF (0) position
Set ohmmeter to lowest ohms range.
Check ohms across AC LINE L1 and L2 terminals. Reading is infinity ohms or OL.
Flip power switch to ON (1) position, the reading should be 1000 ohms or higher.
Check the ohms from AC LINE L1 and L2 terminals to any of the the green bonding screws. Reading is infinity ohms or OL.

Congratulations! You are done.

Grind on.



Unknown said...

Nice thx.

Doing the same to mine.

Could only find a DPST though. GSW-14.
But has the exact same specs as the 15.
Are you running a 1.5hp motor or 2hp?

D. Comeau said...

I am running it at 120V @1.5 hp. Because the switch is powering the VFD and not directly powering a motor proper, we can be confident that the contacts are not going to be abused.

It seems strange that manufacturers rate switches for crazy load ratings like 20A @ 125 V (2500 Watts) but only 1.5 hp, which is 1120 Watts at the same voltage. The reason is that motor loads make significant arcing, not to mention about five times motor rated current to start, which can damage the switch contacts.

The VFD load is capacitive and is much more forgiving on the switch contacts. It's this reason that I would have no issues with using the same switch to power the VFD with a 2 hp motor.


Unknown said...

I have a Couple questions on this much needed modification to the VFD...

1. Will this same setup work on the KBAC-29, as that is what I have ordered for my grinder setup.

2. I assume this is an on/off/on switch, just not wired to that configuration, given it has three sets of terminals. Will a switch of proper voltage/amp rating with just four terminals work the same?


D. Comeau said...


I haven't seen the insides of a KBAC-29, but the same switch wiring should apply to the 24, 27 and 29 models.

The switch I used GSW-15 is an ON-ON double pole double throw (DPDT) with no off position in the middle. Yes, I am only using 1/2 of the terminals. Any two double pole suitably rated switch (GSW-14 or GSW-15) will do.


Unknown said...

Thanks Dan, I'm not real keen on paying $30+ for a switch I can source for easily 1/3 the cost.

Appreciate the knowledge you have shared and continue to share on your builds.