What awg gauge should the 4 wire cable be between a 2 hp 3 phase motor and a Vfd?

LARRYZ10

LARRYZ10

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Feb 6, 2010
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Some of you advised me to use 12awg 3 wire cable for the power cord to my grinder with a 2 hp 3 phase 230 volt motor in place of the 14 gauge wire that powered my 1 1/2 hp motor . The electrician put a 220 receptacle with 12 awg wiring in my garage for a 230 volt 20 amp circuit. My question now is should I change the 16-4 cable between the motor and the Kbac 27d VFD to a 14 gauge cable? Is this a big deal? I already bought the 12 gauge wire and plug and am ready to wire the new 2 hp motor but I worry that the 4 wire cable is too small. Please help me before I bite off my fingernails over this. Any advice would be greatly appreciated. Thanks, Larry Lehman, Bakersfield
 
I think my question is too confusing. I will use 12 gauge wiring from the outlet to the VFD. Do I need 14 gauge wiring from the VFD to the motor? Larry Lehman
 
I use 12 all the way it may be more than needed but error on the side of caution. That motor will pull 7<8 amps on 220v.
 
I figure you'll be drawing less than 10 amps, 16 gauge should work fine unless it's a long run.
 
Use the #12 wiring you already have it will be more than enough. 14 should be enough and easier to work with, as I don't think the motor will draw much more than 5 amps under a load that a belt grinder will need.
 
I would just use the 12 awg for the whole set up. As I said in your other thread, for the good of both the motor and VFD, it is best to keep resistance at a minimum. Because a VFD does its magic by messing with the hertz or frequency being supplied to the motor, as well as the voltage, it's in your equipments' best interest to over size the wire. 14 awg would work fine, but if you already have some twelve to use, use it.
 
You already have some 12 and the terminals on these drives will handle up to a 12, so use the 12. 14 minimum.
 
There is no benefit to using heavier wire than is need for the load of the motor. I don't know the amp draw of your motor it should say on the motor plate. look up the amp carrying capacity of the sixteen gauge wire on the www. rewire if the load is more than 80% of the wires capacity.
 
A 230V 3Ph motor should pull 6.8 full load amps. Your 20A breaker should trip at 80% load or 16A unless it is a 100% rated breaker. In a residential application it is highly doubtful the breaker is 100% rated (they are rather expensive). This means that your breaker (over-current protection) will not trip until it exceeds 16A. You want your breaker to trip before your wiring heats up and starts a fire. So, your wire needs to be rated at or above the trip rating of your breaker. #14 AWG copper wire is rated for 15A at 60 degrees C (which is what most type NM or Romex residential wiring is). #12 is rated for 20A. It would probably be OK to use the #14 wire since your motor should never exceed it's capacity. But I would prefer the #12 (a) to meet the NEC and (b) just incase you want to use that circuit for something else.
 
On the 220V feeding the line side of the VFD you need 4 wires (2 hots, a neutral, and a ground). On the load side of the VFD serving the motor you will also need 4 wires (A, B, C phase and a ground). A neutral on a 3 phase motor is not required. The VFD will convert the 220V singe phase power to 3 phase which is required to control the speed of the motor.
 
I found out since my original post that Beaumont Metal Specialties who makes the KMG grinders sells motors and drives on their website with a download of how to wire the motor to the drive. On their website they specify 14 gauge wiring for all their motors power cables and 16 gauge wiring between the drive and the motor for 1.5 hp and 2 hp 3 phase motors. Th elctrician who wired my garage for 220 at 20 amps said that I should use 12 gauge 3 wire cable for the power cord so I could make it a long one if I wanted ( I am making it 16 feet long) and said that 14 gauge wire would be plenty between the drive and the motor when I told him the motor draws about 7 to 8 amps. The 14 gauge wire must be 3 conductors and a ground wire which is called 14 gauge 4 wire stranded cable. That is what I am going to do when my motor arrives in a couple days. Maybe this information will be of use for other people setting up their variable speed grinders. Larry Lehman
 
The late, great Jimmy Buffett once sang:
"Overkill, overkill
Such a megalo modern problematic ill
Climb too fast and shove too hard
You'll be pushin' up the daisies in some old boneyard "
Click to expand...

Just remember, you should use stranded wire and not solid core from the VFD to the motor. Stranded will stand up better to the vibrations of the motor better.
 
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Here is an interesting observation: I was worried about the wiring between my VFD ( Variable Frequency drive) and my new 2 hp motor. The circuit breaker for my 220 outlet is 20 amps and wired with 12 gauge wiring. I bought 12 gauge 3 wire stranded cable to make up a power cord just to be safe even though the motor only draws 6.6 amps. I was going to use 14 gauge 4 wire stranded cable between the VFD and the motor but I discovered that when the motor arrived and I opened the connections box that the nine wires inside were 18 gauge. Given that information then Rob Frink of Beaumont Metal Speciaties who makes KMG grinders was right in specifying 16 gauge 4 strand wire for the motor connections for 1.5 to 3 hp motors. The 14 gauge 4 wire that I bought is too big to fit the cable glands that hold the wires at the entrance holes in the Kbac drive. Case solved. Larry
 
Aren't y'all glad I'm not the sort of person to say "I told you so" :p

There are two considerations when choosing wire size in this scenario. Ampacity, which is the maximum amperage a wire can tolerate, and voltage drop which is caused by resistance over a distance. The size of the circuit breaker dictates the minimum wire size you can use in the wall and doesn't apply here.

For a short run where voltage drop is not a concern you're left with ampacity. I'm a firm believer of overkill when it comes to electrical, but typical 16 ga will tolerate 20 amps.
 
kcgmann98 said:
On the 220V feeding the line side of the VFD you need 4 wires (2 hots, a neutral, and a ground).

On the load side of the VFD serving the motor you will also need 4 wires (A, B, C phase and a ground). A neutral on a 3 phase motor is not required. The VFD will convert the 220V singe phase power to 3 phase which is required to control the speed of the motor.
Click to expand...

On the 220V feeding the line side of the VFD you need 4 wires (2 hots, a neutral, and a ground).

No, no neutral needed

Strictly 220v , no need to split off a 110v
 
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