Questions about wiring VFD and motor for my KMG

J

J. MacDonald

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Jun 8, 2000
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3,140
I got a NOS Leeson 2hp 3 phase motor and a Toshiba 2hp rated VFD. The VFD is specified to run on 230V single phase input and provide 7.5amps variable frequency output.

I'm fine with low voltage stuff, but an a little paranoid about working with high voltage (read deadly) electricity, plus I don't want to damage anything.

The motor has ten wires coming out of it. I got a basic wiring diagram (which I ould email to anyone interested in looking at it. The motor is rated 230V or 460V. On the diagram it indicatesthat for high voltage L1 (electrical leg I think)goes to T1, L2 to T2 and L3 to T3 and then notes to join and insulate three additional pairs of wires. For low voltage (my application), it indicates L1 to T1,T7, L2 to T2,T8 and L3 to T3,T9 and then join and insulate T4,T5,T6.

Does this mean to wire two wires as specified to each of the three output terminals on the VFD and then twist the other three together with a wire nut? What's the 10th wire for? Ground?

The wires coming out of the motor are all steel stranded. Is #10 solid core a good choice to use between the VFD and motor?

Anyone in the neighborhood want to make a couple quick bucks? (this sstuff makes my skin crawl).

It will be fed from a dedicated 20 amp circuit. Is that enough? Also, how large an input cable do I need from the wall to the VFD?
 
As far as the circuit breaker goes,a 230V 20A breaker will be fine.Without seeing the diagram it is a little hard to tell,but from your info,you are correct in the lower voltage wiring.Most likely the third wire is the ground (look at the diagram,it should show a ground symbol at T-10,or be labeled Gnd. ). If it is a ground,you should connect this wire to the VFD ground,and the VFD to the electrical ground.#10 stranded or solid will work fine.Make good electrical connections.

Stacy
 
Relax!! It looks intimidating at first...but take a deep breath....and take it one step at a time. (hee hee)


OK, here is a diagram of the 3ph motor hook-up:

VFD-WIRING.gif


Don't let the L's , T's and whattever's confuse you. Concentrate on the inputs and outputs to each device. For example, it sounds like your T-VFD's out puts are designated as L1,2,3...? Note in this diagram they are noted as U,V,W...
For low voltage (my application), it indicates L1 to T1,T7, L2 to T2,T8 and L3 to T3,T9 and then join and insulate T4,T5,T6.
Click to expand...
...so you've got this correct. There are 9 wires coming out of the motor. A 10th wire will be a ground and will go from the green screw inside the motor junction box to the chassis lug on your VFD. "green" is the designation for ground....so you'll probably see a green lug on the VFD.


#10 solid is way awkward to work with and a huge over kill for this application. Recall that this motor draws 7.5amp...? (see the nameplate @220V)...anyway, it's not very much at all and doesn't require big wires. There are 3 legs carring the power so each leg is much lower than normal single phase circuits, hence the 3-PH wires can be much smaller. I would use 16ga between the motor and drive. A 20A breaker is fine......which will require the wiring from the breaker to the motor must be rated for 20A +. I think this will about 14GA or bigger. (I'm at home, away from my elec handbooks at the shop so I'm guessing).

not sure if I've made any sense or if I just typed a bunch of garbly-gook...? Let me know I'll try to explain better.
 
So what about the third wire coming from the wall plug? The VFD seems to only want to see two wires. Using a Wiggy, I read 240V across two legs coming from teh wall, and get 120v between each of them and the third terminal. Is that the ground?

I mis counted at first. There's 11 wires total coming out of the motor, the additional two labeled P1 and P2 and noted as STATS on the diagram I got from Leeson. Not sure if that's for thermostat output, or perhaps to connect a tach? Either way, I don't think I need them.

So #14 or #16, four wires from VFD to motor? Will the Flex conduit arc as a ground, or do I need that 4th wire?

don't want to fry the house or myself.

Thanks guys.
 
The third wire from the wall plug is your ground wire.
The P1 and P2 wires are for an internal (inside motor windings) thermal overload switch. This protects the motor from getting too hot. If it were me, I would completely disregard these two wires and not use them---just tape them off. Your VFD will provide the needed motor protection. If you want to use them then you will need to run these wires in series with the stop circuit of your VFD. (the idea is to act as an aditional stop switch if the thermal reaches it's 'trip' point).
I would recomend # 14 wires to the motor. In many of the areas I have worked (I'm a journeyman electrician) the inspectors don't like to see any thing smaller than #14 on a motor over 1 hp.
As for the wire size required on a 20 amp circuit---#12.
Yes, you will run 4 wires to your motor from the VFD. You will have the three phase conductors and a (green) ground wire. The ground wire termination points should be a green colored screw in the motor junction box and at the VFD.
Flex conduit can (in many cases) act as a grounding conductor, but still it's better to use a wire---it's approved in all cases and will always work as intended.
Do NOT run your motor with out a ground---it could save your life!

Mike
 
With all the help I got from you guys I was able to scrape up the nerve to tackle this thing instead of waiting for/paying a real electrician to wire this beast.

The I ended up using 4 colors of #14 in 1/2" flex from the VFD to the motor. I used #12 x 3 for the power cable from the wall plug to the VFD and a 20 amp twist lock plug.

When I had the shop wired a year and a half ago by a real electrician, I had him put in a 75 amp sub panel just for the shop (200 amp new service to the tiny 1150 ft house) and pull wire for a 30 amp circuit to everywhere I wanted 220 (five locations) in case I ever got something bigger, but we terminated all with 20 amp breakers and twist lock plugs. Now there all full powering my Bridgeport mill, Hardinge lathe, Rockwell 1.5hp dust collector, compressor and now my KMG!

With this newfound energy, perhaps I'll finally get around to installing the other VFD I have on my step pulley mill.

FYI, to make sure it doesn't just work, but is safe, I checked the grinder/motor chassis against the hard conduit on the wall with a multi meter and am getting less than .01 volts A/C :)

Thanks for all the help guys. It really means a lot. I'll post a pic or two in a new thread for those with curious eyes.
 
John

Just got online this evening.

It sounds like you've got it connected right if you have only 0.1Vac between the motor chassis and the conduit. If the motor chassis was not grounded properly, you would get anything from a few volts up to 20 to 30 Vac.

Mike is most likely right about the P1 and P2 connections from the motor. Depending on the VFD, you can do as he says and put it in series with the stop button or connect it to another input and program it to be a stop. This is a pretty common way to do it so the manual would probably have a wiring diagram showing this connection scheme. You should be able to use pretty thin wire (20 or 22 AWG) for these connections since they would not carry any significant current but the wire would still have to have insulation good for 220Vac, which may lead you back to using something like 14 AWG. Mike being the electrician would know the electrical code requirements better than I would. I don't have a copy of the manual at home so I can't confirm this about the model of VFD that you bought.

Pictures would be nice. It certainly sounds like you have a really nice shop set up.

Phil
 
Phil, thanks for the observations. I likely will ignore the P1/P2 leads as teh rig seems to work fine for now.

None of this would have happened if not for you.

Thanks bro.
 
Glad that I could help someone out in some way after all that I have learned, but have not really had the time to apply.

Leaving the thermal sensor in the motor unconnected should be fine. I think that they put those in for large, complex industrial applications where there is no operator near the motor. The overheat condition would then be communicated to the VFD. The VFD would then shut down and pass the fault information on to a central monitoring system.

Phil
 
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