Protecting my Variable Frequency Drive

[Tom Bender]

My 120 volt VFD powers a 1 hp motor. Apparently lightning took it out. The tech guy at Teco said I need to protect it from spikes in both the hot and neutral lines (L1 and L2) but not the ground. He said a surge protector will only break L1 and a UPS will do no better. Best thing is to unplug the 120 volt power when not in use. Too much trouble.

So in discussing with my brother the electrician we came up with a better plan. Install a double pole relay that is on when the shop lights are on. The double pole will break both lines. Since I am only in the shop about 20 hours a week the survival odds are much better. It's still a lump of hardware to buy and install somewhere.

Any better ideas?

[Lon Crosby]

Just replace your single pole switch with a double pole switch.

[Bill Jobe]

I was shock (pun not intended) to learn that GFCBs do not eliminate the posibility of electrocution. My son-in-law explaned the reason but I still don't understand.

[Mike Heidrick]

I use a switched disconnect.

I would optisolate the coil on the contactor if using a lighting circuit to control anything switching the power to a VFD.

[Bill Dufour]

Simple wall switch to supply power to the vfd. use a two pole switch. A line reactor might help a little. Check ebay or make you own. You will only use two of the three coils. I have never seen a two line reactor only a simple one line torrid or a three line unit.
I suppose you could put a big line reactor on the main shop power supply. really a good idea if you have any big motor loads or welders to protect the house electronics.
Bill D.

http://www.eaton.com/ecm/groups/public/@pub/@electrical/documents/content/ap040004en.pdf

[Tom Bender]

Since my shop has finished walls I was hoping to not have to run new wiring. Guess adding a DP switch next to the VFD would work out. Just one more step in running that machine.

[Tom Bender]

Just replace your single pole switch with a double pole switch.

Good idea but the operating switch is in a control circuit, not the power feed to the device.

[Bill Dufour]

My VFD's all have a fan which is on all the time they are plugged in. For this reason I like to have a disconnect switch for each machine. I only turn it on or off after the machine is at a dead stop. It is not intended as an emergency stop.
On my 3hp lathe I used a power relay and a 3 wire control station with a indicator light.
A easy way to remember to turn them off is to have machine light run from the main switch that is on whenever the vfd is powered.
Bill D

[Tom Bender]

Thanks Bill, I had forgotten about the fan. The new DP switch will turn off the display but I can leave it on briefly after a hard run. (not sure what operating conditions warm up a VFD) If the display is still on as I leave the shop it will remind me to switch off.

[Bill Dufour]

My drill press is actually powered from a overhead 240 outlet. So I have it wired with a 120 outlet in the same box as well. I plug in my dp light into the same circuit. That way I see the light and display on when I leave as I walk by the breaker panel.
Bill D.