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Basic Vfd Questions


Active Member
Active Member
Hello all,
I am in the process of installing a 3 phase motor on my Clausing 8520 mill and have decided on a TECO N3-202-CS VFD. I have been reading the manual online and have a pretty good idea about the overall ideas such as wiring and programming. Couple of basic questions:
Is there an on/off switch on the VFD or is it always powered up as long as the circuit feeding it is on?

What type of wiring is suitable for running from the VFD to remote switches near the mill for start, stop, forward, reverse and speed?

Thoughts on enclosure for the VFD? Cooling fan?

Thanks for any ideas and if someone has some pics of their installation please post those too.



Active User
H-M Supporter-Premium
I have Teco drives on my mill and lathe. They seem pretty bullet-proof.

The drive does not have a power switch, turn off the breaker in the panel or just leave it on - they draw practically nothing at idle.

The control circuitry is low current at less than 24 volts and you can use most any wire for the controls. The limiting factor is if the wire is exposed or runs across the floor you want something rugged enough to withstand that service.

The VFD probably already has a cooling fan built in. I would not bother with an enclosure, just mount the unit on the wall so you can see the readout and get to the keyboard controls easily when you need to tweak the settings.



Active User
H-M Supporter-Premium
A few things to consider, the manuals usually give some guidance as to wire gauge and type. I use shielded wire for my control lines (12-24VDC usually a few milli amps of current), unlikely you would have any issues with short cabling, but worth the additional safety if you are going remote controls more than a couple of feet away. I usually use anything from 18-22G stranded wire cable, something like 6C or 7C (depends on the controls and remote speed pot). I would use 3 wire control on a mill, very simple. You would probably want an E-Stop, speed control, momentary off, momentary on, spindle direction. Maybe an inexpensive tach. but this would require a 12VDC power supply. http://www.hobby-machinist.com/threads/why-use-a-switch-button-panel.50646/#post-425598

The VFD to motor cable can generate a lot of electrical noise, I know of a few people that have had problems. If you have longer motor cable runs (more than 4') you might use flexible shielded conduit or shielded cable, since it is 3 phase, you need 3 conductors and a ground (separate from the shield drain wire). It is recommended that the shields all be grounded at the VFD. If you are going to use a remote speed pot, the cable should be shielded if more than a few feet, something like 22-24G 3C or 4C. Without the shielding I have seen significant noise/jitter picked from 6-12' unshielded speed cables. In any case, do not tie the motor cable with the signal cable wires. In a mill, with very short wiring distances, electrical noise may not be an issue. I just follow the manual recommendations, and have not had any problem with dozens of VFD systems.

Do not use a household GFI, they will usually trip with a VFD. Industrial GFI have a higher trip point and are less likely to be a problem with VFDs.

If your VFD is going to be exposed to chips or spray, you might consider an enclosure. The need for venting/fan is often a function of the cabinet size and the VFD ratings/fan settings. On a mill, the work load is pretty light on a manual machine. If you do use an enclosure, you might consider some passive venting, either 4" aluminum screened soffits or computer fan screens. Heat kills the electrical components, especially electrolytic capacitors in the power supply. I have seen mill installs w/wo enclosures, but if you think it could be exposed to flying chips/coolant than use an enclosure or a box with an open front. This can also depend on the VFD Nema rating, the Teco N3 is Nema 1. Different options, on a mill I would keep it pretty simple.


Global Moderator
Staff member
I leave mine powered up all the time. Turns off with the breaker in the panel if needed.

Any 8 conductor cable will work for the switches, stranded conductor CAT5 ethernet cable would be fine. Cheap and available anywhere.

Here is how I did mine:

Mounted the VFD on the back of the electrical cabinet, but it could mount on the back if the mill or on the wall. Most of the cables you see here have nothing to do with the VFD.

The way I had mine lashed up before I installed the new VFD is just to mount the VFD on the head in place of the original switch. Just operated it from the front panel.


Active Member
Active Member
Thanks all for the info. I'll be buying a VFD soon. Have the 240 v single phase already run in EMT to the mill location. Will try to post pics once I get everything set up.
Thanks again,