OK, I finally acquired a Siemens VFD for use with my lathe and mill. I've seen several posts about not putting a forward / reverse switch between the motor and the VFD. Would it be OK to put an emergency shutoff switch between them as I would hate to have something be flailing around and trying to press the little Off button on the VFD? I guess I could put the emergency shutoff between the power and the VFD if that would be better.
Thanks. Steve.
You can wire a start/stop button with three wire control to the appropriate terminals on your VFD. Not a "hard" disconnect but it will stop the machine as long as the electronics in the VFD don't go haywire.
Instead, use the low voltage controls provided with the VFD (at least all I've seen). You can use the switches and pot of your choice to control stopping, starting, reversing, and speed. Mount the switches and pot in a small junction box at a handy location on your machine, and run a separate emt or conduit for the control functions.
You don't need horsepower rated switches. Your VFD manual should give specs for controls. This approach also lets you mount the VFD on the wall out of the way of coolant or oil, and still see the display. The Mitsubishi's I use have two displays, allowing the display of both speed and some other variable. I chose to display amps, which is very helpful to gauge how much depth of cut I can use.
Pete Keillor
If you really don't want to implement the low-voltage VFD EPO function as others have suggested, or if you simply don't trust its operation in an emergency, you could wire the input power to the VFD through normally closed EPO buttons at each machine.
I would opt for the low-voltage control functions myself.
Jim
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Would it be OK to put an emergency shutoff switch between them as I would hate to have something be flailing around and trying to press the little Off button on the VFD?
Most VFDs support "maintained" or "intermittent" controls, as options.
One option on a VFD I have is the usual N.O. START, N.C. STOP "three wire" control, with the STOP also being an EMERGENCY STOP, "mushroom" switch.
The connection from the load side of the VFD to the load motor should be as direct as is practical.
No components should be interposed.
In fact, on account of the high voltages present ... 325 volts peak-peak for
230 volt drives and 650 volts peak-peak for 460 volt drives ... which exceed the rating of most cordage, special wiring may be required.Belden makes this special cable, which is also shielded to reduce EMI.
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