Line In to VFD....

silver_pilate

silver_pilate

Joined
Oct 30, 2002
Messages
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I'm in the process of wiring up a VFD and motor for my KMG and have a dummy question for the sake of my safety.

In my shop, the 250V outlet is of the 50 amp variety with 4 prongs (3 spades and a rounded ground). I have a RV type extension cord to my grinder from the outlet and an appropriate male plug/pigtail that will be wired to the VFD.

I know the lateral most spades on the plug are the 125V legs and the rounded prong is the true ground, and the middle spade is the neutral leg. The Teco FM50 2hp drive I'm wiring in has inputs L1, L2, L3. Here's the labeling from the manual:

VFD2.jpg


L1/L (R): Primary power source input to Drive
L2 (S): Single phase: L1/L2 or L/N
L3/N (T): Three phase: L1/L2/L3

Here's a copy of the basic wiring diagram from the manual as well:

VFD.jpg


I understand that L1 and L2 are the 125V leg connections, and I know that I will ground the VFD (and motor frame) to the true ground, but what do I need to do with the neutral wire from the pigtail?

Thanks!

--nathan
 
I would clip the neutral wire or tie it in with the ground being that a neutral is another ground.
 
As for connecting the neutral to the ground, doesn't the neutral line carry the difference in current when the loads on the two hot legs are unbalanced? Should I just cap it off instead?

--nathan
 
You should NOT tie the neutral to the ground. It probably won't hurt anything, but standard electrical good practice is to have the neutral tied to the ground in exactly ONE place: the main breaker panel. The reasons are varied and subtle, but the biggest is to prevent ground loops...and you probably don't want a technical explanation of that one.:D

For anything that will only use 220VAC, like your (older) clothes dryers, hot water heater, etc. the neutral is not needed and you frequently find 3 wire/prong plugs used for that reason. Some newer dryers and such do use one leg for 110 VAC in the controls, so that requires the neutral line...and a 4 prong plug.

It is likely that a VFD only requires 230 VAC and will not need the neutral line. The best solution is to see if your VFD has spare/dummy terminals and land it on one of them. Capping it off with a wire nut is a good second option.
 
Hello Nathan

Sorry I did not reply to you sooner. We are pretty busy with our boys, getting ready for their robotics competition.

CDH is correct about not connecting the Neutral wire to Ground.

I am guessing that you have a Teco FM50-202-C. From the wiring diagram on page 17 and te table describing the terminal connections for terminal block TM1 on page 19, it looks like you should connect the Neutral wire to the L3 terminal. The diagram on page 15 shows how the optional noise filter is connected and are not relevant if you do not have one. Page 21 of the manual has a picture of the front of the VFD with an "L-shaped" piece of metal that would be attached to the lower left corner of the chassis with an M4 screw. You should crimp a ring-lug on to the Ground wire and attach it to this L-shaped piece.

You should be using a 4-conductor cable to connect the output of the VFD to the motor. Three are for the three outputs (T1-T3). The fourth is a ground wire and should also get a ring lug and be terminated at the L-shape. The other end of the ground wire should be connected to the chassis of the motor.

According to the table on page 13 of the manual, all of the input and output wiring should be at leas 14 AWG to carry the currents safely though it may be easier to find 12 AWG. In industrial applications, the inputs and outputs are typically wired using "SOOW" cable with 3 or 4 conductors, as appropriate. I have seen it at some Home Depots but you may have better luck finding it at an electrical wholesaler.

Let me know if you need any more information.


Take care.

Phil
 
Phil, I appreciate your time. I understand about being busy.

I went ahead and put a cap on the neutral wire and left it unconnected. The description for L3 seemed to point to it being necessary for a 3 phase input but not a single phase. It seems to work fine and is powering the KMG well. I ran all my input and output through 14/4 stranded cord. As you and the manual suggested, I ran my grounds to the grounding terminal that I installed to the chassis.

I worked my way through the manual to figure out now to set up external controls for the speed pot and fwd/stop/rev. The only other settings I changed from factory were to set a min/max frequency (3Hz min, 90Hz max for the belt speeds I wanted) and I upped the torque compensation gain (F13) to 6% to get some better torque down low.

Any other suggestions on how I should tweak the drive to get the most out of my machine?

Thanks again for your time and expertise!

--nathan
 
silver_pilate said:
the 250V outlet is of the 50 amp
Click to expand...


silver_pilate said:
I ran all my input and output through 14/4 stranded cord.
Click to expand...

This is a serious hazard. If you have a 50 amp circuit breaker (as required by code...the outlet rating must match the circuit breaker and wire ratings) it is quite possible to melt the wire from a slow overload before the breaker trips. It is possible that a hard short will trip the breaker, but a full load of 50 amps will heat the wire enough to melt the insulation without tripping and could actually melt the wire and start a fire.

When I got into my house the previous owner used #12 wire for the hot tub. Who checks those things? Not even me, the electrical engineer. Yep, 50 amp breaker. I went to add a circuit for a workbench and touched the wire. The wire burned me...through the insulation.

I don't have the charts here at home, but IIRC the US National Electric Code requires #6 wire minimum for a 50 amp circuit...meaning your #14 wire is 4 trade sizes too small.

I size power distribution systems as part of my job and I am very conservative for good reason...you don't want to screw around here. Been there, done that, got the scars...please verify and match the circuit breaker to the wire and plug sizes.
 
I ran the extension from the plug to the grinder using a 6 AWG extension cord desgined for RV use. There is a short (3 foot) length of 14 AWG stranded cord into the control box. The controller calls for 14 guage input and output on the terminals. The motor should only pull about 10 amps max.

What's your suggestion as to my course of action. There's no way 6/4 wire is going to fit on the VFD terminals. As I rent my shop, I don't know that I can have an electrician change the outlet. I definitely want to be safe here.

Thanks for your advice.

--nathan
 
Thinking about it this morning, since I'm running on a high amp capable line, and I don't want my controller to go "pop" with a surge some day, I'm going to put together a small box with a fuse terminal, say 20 Amps, between the #6 extension and the #14 input to the controller.

Sound like a plan?

--nathan
 
CDH, being the dunce I am about electrical, I assume I fuse each hot leg, but what size fuses do I use? 20 amps on each leg? Or do I cut it in half and say 10 amps on each leg? And also, it shouldn't matter where in line I place the fuse box within the #14 wire, correct. Can I just place the fuse box within my clean box at the end of the 3 foot 14/4 wire before the VFD, and when it sees loads beyond the fuse, pop, and no overheating the wires?

Thanks for your expertise!

--nathan
 
You can place the fuses anywhere so long as you have the #6 'upstream' and the #14 'downstream'. You could hang the box on the wall beside the outlet if you want so you only have the smaller cord to mess with over any length.

Yes, you need 20 amp fuses for both legs, as you will have the full amperage flowing through both of them. The intent is to have protection against fire, not really to protect the VFD. The VFD is required to fuse or otherwise protect it's internals (at least from fire hazard) in order to pass UL certification for sale in the USA.

If it makes you feel better, you can reduce the amperage of the fuses to the next standard size above the max current required by your VFD+motor combination, but you really gain very little by doing so. Be sure to get 'slow blow' or 'time delay' fuses, though that is the standard offering in this size and style of fuse. Fast blow fuses are made to protect sensitive electronics and such from surges but blow when a motor starting surge hits them.

Have fun with your new toy!!!

-Clayton
 
There is a difference between dedicated circuits (like for Clayton's hot tub) and circuits where it is not know what will be connected. In the later, the 50 A breaker is only meant to protect the supply. Each piece of equipment connected to the supply is expected to take care if itself.

Input fuses or an input breakers sized to 125% of the input rating of the VFD would be standard industry practice. For the 1.5kW max rating of your particular VFD, you would have a maximum input current of 6.25 Amps. Multipying by 125% gives 7.8 Amps. You could use an 8 Amp or 10 Amp slow-blow fuse. They need to be slow-blow so that the in-rush current of the capacitors in the VFD do not cause them to open. The VFD should limit any surges from the motor, if it is designed properly. Use two of the Littelfuse Omni-Blok fuse holders inside your clean box. They are rated at 300 Vac for UL and the fuses can be found everywhere, unlike the 600 V style. We use similar fuses and holder in the 240 V circuits of the big motor drives and UPS' that we design. Connect the fuse blocks to your VFD with 14 AWG or 12 AWG wire. With this, you can also use 12 or 14 AWG to connect from your plug to your fuse holder. 6 AWG is pretty big for this sort of application and you may have trouble finding a way to make the connections.

www.newark.com/littelfuse/0218008-hxp/cartridge-fuse/dp/26K8064
www.newark.com/littelfuse/0218010-mxp/cartridge-fuse/dp/42K9387

www.newark.com/jsp/search/productdetail.jsp?CMP=ILC-1c126onlinecatalog&sku=69K7674

Unfortunately, not all VFD's are designed with input fuses due to competitive cost reasons, especially under 50 hp. As long as the product meets UL's definition of "safe" after the tests, the product gets their certification. Most of the people I know that actually have to deal directly with UL do not have a particularly high opinion of them.
 
Nathan, can I ask where you bought the filters and how deep is the box you put the VFD in?

I am in the process of doing the same with PSO's gracious help.

Pad
 
Pad, I bought the filters at an Advanced Auto Parts store. They're just some generic carburetor filters. They usually sell them in the "performance" type section rather than in the filters area. I used RTV silicone to create a seal to the box. I've got a few pictures on my website. I'm not sure on the depth of the box, but it allows about 1 - 1.5" of clearance between the lid and the VFD. Rather than mount the controls on the lid, I ran flex conduit to a project box on the grinder plate.

If you have any questions, I'll be glad to help if I can.

--nathan
 
I will do the same Nathan. The VFD will be about 14 feet from the grinders.

Thanks a bunch and I will surely take you up on your offer cause I am not the brightest of the bunch and PSO might have his hands full here. ;)

Pad
 
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