In this particular situation, unfortunately I have a 240V lathe with a VFD. I'm wondering if wet sanding some very thin green wood turning would be interesting, but thought GFCI protection would be desirable. Asked on the Messages forum if anyone has seen a 240V GFCI receptacle (no). Several replied that their 120V lathe with VFD kept tripping GFCI and had to switch to unprotected receptacle.
So, anyone wet sand on a 240V lathe with VFD, and if so how do protect yourself against mixing water and electricity?
I do it all the time. I usually drape the lathe bed with plastic or cardboard, but so far, haven't done anything about a potential shock hazard to me, or damage to the electronics.
I have a PM 3520-B, so the motor and the VFD unit are pretty well out of the way of any water. I use enough to produce a slurry, and dip the abrasive in a bowl of warm water. but not enough to spray water all around the room (or in my case, barn), but I do get a visible stain on the plastic partition between the lathe and the next stall in the barn.
Maybe someone here can point out the error of my ways, and precautions I should be taking (?) I've never considered the electric hazards, but did want to limit the mess and corrosion to the lathe bed. A lathe with an under-slung motor down below the headstock would probably be another matter.
I agree with Brad. The body and all of the exposed parts of the lathe are already grounded. Adding water to the situation does not make you more grounded. There is one point of possible, but unlikely, concern however. If you are power sanding with an AC powered sander, it is conceivable that water could create a conducting path from within the sander to your hands. That small risk could be dealt with by using a 120 V GFCI.
I agree with Dennis as to where the most likely (but low) risk lies and it can be mitigated with a GFCI.
My General is of course grounded and the motor and VFD are well protected from water spray. The motor being a TEFC inside the cabinet is thus is very well protected. If I was paranoid, I'd add an extra ground bonding wire from the lathe frame to a known ground just in case the first ground wire in the power cord should break.
Don, I'm not an electrician but I have spoken with several electricians about this. The short version of the story: variable speed motors and GFCIs do not get along.
I had my lathe on a GFCI for a long time and I could not figure out why it was frequently tripping the circuit. Finally several electricians told me to plug it in to a non-GFCI circuit. I haven't had any problems since I did that.
As far as wet sanding goes, I've never had an issue with wet sanding on a lathe.
I am with the others who do not recommend VFDs and GFCI.
I have a NOVA DVR XP. The manual states it is not compatible with some GFCI.
I plugged in the NOVA and it tripped the GFCI without even turning on. Something about the electronics made the GFCI detect current on the ground.
I have used wet sanding on the lathe with no issues. Not a liquid bath, just a liquid film between abrasive and the wood.
I have had a lot more water flung out from green wood than from wet sanding. I normally worry about water on the lathe bed causing rust rather than the potential for electrical problems.
I did a bit of Googling and one person, perhaps more, claimed to have cured the GFCI tripping by looping the wires powering the VFD through ferrite beads/toroids. This would cut the high-frequency harmonics and I could see it possibly working.
In the OP's 240V supply case, it would be a rather expensive experiment if it didn't work!
