What materials do I need to wire a VFD to a three phase motor?

Hi everyone,

I am part of a senior design group that is building a dynonameter to test shocks. We are ordering parts tomorrow morning and so I want to make sure that I am not missing anything. I do not have any experience with VFD's or three phase motors but I am doing my best to research and learn more each and every day.

On my parts list I have a three phase motor, a DURApulse GS3-21P0 AC Drive, an input fuse kit for the VFD, a USB to RS-485 adapter (for MODBUS communication), a load-cell, and a temperature sensor.

My question is: To wire the VFD to the motor what will I need? I assume both the VFD and motor do not come with any wires. I need to connect the VFD to a three phase 50Amp outlet that will be used to power the VFD. My guess would be to order a three phase extension cord off a website like Amazon and then cut off one of the ends off and use the leads to wire to the VFD. Any thoughts? I was thinking perhaps an extension cord like this one; https://www.amazon.com/Conntek-RUL6...d=1481208227&sr=8-2&keywords=250VAC+extension

**Note: The extension cord in the link above is a 30Amp-250V extension cord. The power supply outlet is a 50Amp outlet. The motor will only draw a few Amps of current. Is it safe to assume that the extension cord provided in the link will be ok for use (provided that prongs are compatible) along with the VFD and the Power supply outlet?

Thank you!

-Kevin


The Shock Dyno Control System
There will be two phases, a warm up phase and a test phase. The warm up phase consists of running the motor until the shock reaches a desired set temperature, when this happens the motor will stop running and there will be a small delay before automatically proceeding to the test phase. Once the test phase starts, the motor will start again and will run until a desired RPM is reached, during the test phase a graph will be plotting force (from load cell) vs RPM.





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Ok, I seem to recall this is for a College class yes?

Please find someone with a Minnesota electrical license and have them assist you. Your college should have at least someone in the facilities group if nothing else.

There are code requirements for doing this sort of thing that you shouldn't mess with.

That aside, the NEC has the tables you'll need to size this correctly.

Agreed with the fact that you MUST have an electrician do / supervise this project. You could damage equipment or more importantly damage to humans could occur.
Another thing you should consider is at very least a load reactor sized for the job and perhaps input filtering as well. Also, be SURE to use drive rated cable. I see to may installs nowadays where people think its ok to not use drive cable. Save yourself the headache and do it right the first time. The drive manufacturer's manual should have connection diagrams. Follow them!

Safety first

It is not as simple as put a cord on, and off it goes. A three phase motor and drive uses high voltage and can cause death.

You mention load cells and other controls, what are they going to?

As said this is not a DYI project, life safety is involved.

Wow! not asking much then....get some assistance locally.

what power and voltage rating is the motor? "takes a few amps" and you have a 3-phase 50 amp, and you want to use an extension cord?

Over here we would specify a steel wire-armoured cable (3 core minimum, maybe even 4 core) for a motor. It would not be connected directly to an outlet, but through a suitably-protected motor isolator.

But then you have other devices, which should be mounted in a panel that will need a power supply (probably single phase).

Suggest you draw out what you have and what you think you need, use the manuals to confirm any wiring requirements, check your current ratings of all devices. Work out a suitable power and wiring schematic, complete with rated fuses/circuit breakers. Enclose it all in a metal panel, for your protection. Get someone qualified to assist you in specification and build of the panel.

If this is just a design exercise, then you have to go through all of the above.
If you are actually going to build and test this, then yes, do it carefully and competently.

Refer the electrician to the manual, one page of which is shown below:

In addition, the extension cord you listed as an example is for single phase only. Three phase requires a ground conductor as well as the 3 phases.

belae1ka,

you mention a load cell and yet you have not mentioned what you are connecting it to.

load cells and thermocouples put out millivolts.
what is the device that will control your test?
how are you going to record the test data?
what is the dynonameter torque you are looking for?
have you taken into consideration the shock factor for the load cell, and that shock can be 6-10 times greater than the load cell can handle.
what type of load cell is it?
do you have load cell stops?


what you are wanting to do cannot be simply thrown together in a few hours
and from your details, you have not planned for everything or left out some details.

as already pointed out, you must go by the nec code.
URGENT WARNING !!
please get an experienced electricial person to help!
Safety first, yesterday, today, tomorrow, and forever !

not slamming you.

regards,
james

WOW

A recipe for disaster waiting to happen.

Get someone qualified to help out here

Lives are at risk here

Brian

Alright, so I am going to assume that you have qualified supervision here, as it is for a class design project.

There are a LOT of code requirements, and I will give no information rather than incorrect information.

The first thing you need to do is look at the Full Load Amperage (or FLA) on the motor nameplate. You will size your fuses to 125% of FLA.

What is the voltage on your power supply?

It will be much cheaper to order a male plug and a length of properly sized SO cord.

Next you need to look at the wire size you will need in the NEC. Does your classroom provide the cable you will need? This is very important because if your wire is too small then it will quite literally blow up.

The people above are right. Motors often carry enough current to cause real damage to people and property.

The next concern is your drive. You need to realize that there is 600VDC inside this drive and some huge capacitors and transistors that can easily blow up or shock you even if the power is removed. If you remove power from the drive, wait 10 minutes then take a reading on the DC Bus terminals to verify that you are getting 0VDC before you do anything with the drive. I have seen these things blow up, and it will scare the **** out of you.

Post when you have the above information, and we can go from there. I would also like to know if you have qualified supervision for this project (someone to inspect the wiring prior to you powering on the system).

For a permanent install, you would hardwire inside conduit.
The drive is 1HP. 3 phase input is 6 Amps.
50A Plug is Hubbell CS8165C. Levington is cheaper.
I don't like using a 50 Amp service for something so small. But, if you must, you still need to use large SO cord for safety. I suggest 6/4 SO.
The drive and fuse kit need to go inside an enclosure with a disconnect. 20 x 16 is probably a good size. NEMA 1 is minimum. I prefer NEMA 4. Don't forget backing plate.
Disconnect.
I don't like disconnects and fuses. MCCB makes more sense.

Wire to motor. If it's inside conduit, then you can use 12 or 14 gauge TFFN/THWN/MTW.
If it's not in conduit, then you need VFD cable. If you use standard SO, the radiation might drive nearby electronics crazy. Might not be a big deal at 1HP.

What is the control system? PC or PLC? Mount PLC inside enclosure as well. What about operator interface? HMI?

Stop!!!!!!! Go no further until you have qualified help at your side. You will learn more of the right stuff that way and you may survive to do it again someday.

VFD's are deadly. They have their own unique set of hazards requiring unconventional safety precautions. Any instructor turning a student loose with this little prep is asking to get someone seriously injured or worse.

Further, once you get it hooked up, what are you going to do to program the drive. It's not Plug and Play. The life of the motor as well as your life is further at risk due to the programming not being properly done.

I'm not trying to be melodramatic. I've done this for almost 30 years and have almost killed myself twice. Fortunately, as far as I know, I've not hurt anyone else. I pray it stays that way.

If your boss is giving you a tough time on funding ask which is less money: hiring a qualified electrical contractor or defending the law suit from your insurance company?

I get the vision that it's a small shop. The only source of 3 phase power is the 208/240 socket for a welder or forklift charger. This is R&D.
The VFD is only 1 HP. He has a fuse kit. I get the impression he is smart enough to connect it properly. As I said in my post, I don't like using a 50 Amp source for a load one tenth of that, but if that's all he has, I suspect that's what he's going to use.

He spelled out his concerns in large blue type, and asked about the safety of the cord. it needs to be sized for the source, not the load. We want the breaker to trip if something cuts the cord. Minimum is 6 gauge, with 8 gauge ground. 6/4 is easier to get. That's what I suggested.
You don't need a journeyman to connect a Hubbell Twistlock and SO cord. Just common sense, like anything else.

I expect the drive default mode is V/F. It can be Plug & Play in this mode. He wants Sensorless Vector Mode to get RPM feedback. For that, you need to set the mode and Autotune. Still, I would call it almost Plug and Play.

Again, the drive is one horsepower. 750 Watts. Even if he blows up the drive, I doubt he will level the town of Mt. Pleasant, Michigan.

keithkyll said:

Minimum is 6 gauge, with 8 gauge ground. 6/4 is easier to get. That's what I suggested.
You don't need a journeyman to connect a Hubbell Twistlock and SO cord. Just common sense, like anything else.

Click to expand...

And a BIG screw driver