static shock

L

Les Rachlin

Joined
Jan 21, 2009
Messages
2
Hi, I need a little advice. Now that the air is so dry I am getting multiple shocks whenever I use a grinding belt of 400 or finer. I have tried rubber coated gloves without results. I have thought of using a shock wrist band like the computer guys do. Basically a wire from the wrist to the grinding machine. The thing is I know nothing about the details of the electricity I am generating and wonder if grounding myself to the machine is safe. What do you guys think? Les
 
You could probably solve it by grounding the chassis of your grinder. A build up of dust on your grinder could also cause a static charge to build up if its not grounded, so you might consider blowing it down. Also, if your grinder's motor isn't sealed it can get metal dust inside and cause a small short.

Before grounding your chassis, however, you should examine the wiring to ensure you don't have a short. If there is a short and the chassis is hot, you could have a dangerous situation on your hands. The fact that you get shocked when using finer grit belts might only be a coincidence.

You can test it by putting one lead from a multimeter on the chassis and the other to the ouputs at the switch, making sure to measure across both the positive and negative leads. You should also measure from the chassis to a known ground. I often use the third hole in a wall socket, as it is a known ground. It must read zero in each case. If not, you need to investigate your wiring, or the motor itself.

Start with the simplest things and work backwards from the power supply, which in this case with the power cord, then the switch, then the motor and/or chassis.
 
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Absolutely do not have a wire from your wrist to the grinder. If it catches in the grinder your going to the hospital. I agree with bjlongi sounds like you have ground fault. Check the wiring in the outlet you are plugged into and make sure it is grounded.
 
OH, and I forgot to add. Don't wear a wrist band to ground yourself. It's unsafe and could result in a shock going across your chest in order to exit out of your other arm.

Wrist bands are primarily used to protect electronics from static shocks that our bodies build up, not the other way around. They are also intended for use with electronics that aren't powered up.
 
Yep, tis the season for the static shocks:(. If you slack belt grind on almost any grit you will get zapped but good whenever you come in proximity of a grounded object. In the dry winter air having your body ungrounded and putting metal you are holding on the ungrounded belt essentially makes you and the running belt into a human Van de Graaff generator building up a pretty good electric charge that will be discharged at the nearest ground opportunity. This will often happen when grinding and a finger or knuckle gets too close to a part of the metal frame of the grinder. There will be a little arc, a snap and very unpleasant sensation at the point of discharge. It would be just a humorous event except that when grinding your attention is so focused on what you are doing that you are almost in a trance and this sudden shock can lead to a much more serious accident when you react.

I use the slack belt a lot on sword geometries and so can build up very large charges. I have had arcs over 1" in length jump between me and a metal objects, and I have a tool rest arm that sticks out at around groin level:eek:.
To deal with it I have put a small chunk of chain in my waistband in the back and tossed the other end over my grounded drill press frame that is near the grinder, it helps. Another thing you can do is quickly tap the grinder frame or any grounded object with what you are grinding frequently between passes. This will keep the amount of accumulated charge much smaller by not allowing it to build up for when you don't expect it.
 
Thanks for the help guys. I tend to think it is from the slack grinding and not a short as it only happens when slack grinding and never using a wheel. When you say use a machine that is well grounded...doesn't the third prong on my grinder and buffer plugs ground the machine ok? I don't have any seperate grounding wires hooked to either machine. Ok so I am not a machinist. Les
 
There was another discussion of this issue, the only way I found to reduce the static is to put a wire to ground on the back of the belt. I put a wire under a screw and bent at a slight angle to where it remained in contact with the back of the belt. This greatly reduced the static.

I checked my grounds and all are good even the socket, I also tried grounding myself but that jus resulted in a continous flow of electricty through me and that was uncomforatble, the wire is the only way I have found to reduce the shock, there is still some but doesnt look like a lightining bolt.
 
Try setting up a platform of 2x4's with a piece of plywood and stand on that and see if it still happens.

Either try more insulation under your feet or less. Less will make the shocks smaller and you'll probably feel the shocks going through your feet if you feel them at all. Maybe wearing an old worn out pair of shoes with non-rubber soles will also make a difference if you're standing directly on the floor.

You may also try wearing something that doesn't hold static electricity, like cotton.
 
Spray the back of new belts with an anti-static spray for fabric like Static Guard. Works well.
While it doesn't protect against static, it never hurts to ground your motor casings to an earth ground.
 
The third prong on the grinder only works if the rest of the wiring is in place. Does the wiring go through metal or plastic conduit in your shop? If it is metal it's likely a static issue. If it is plastic make sure there are three wires continuously going back to the breaker. Check each junction box on the way back to make sure their is continuity for the third wire.
 
In dry months when this is happening to me, I have one of those rubber intermeshed floor mats. I stand on the rubber mat and no more shocks. If you're building up a static charge and you're the best source for that charge to go to ground, then you'll get shocked. If you isolate yourself from ground with a floor mat, then you're no longer the best source for ground.
 
I have the same problem Les does, though not with my belt grinder. It is with my buffer. The simplest solution so far as been to just touch the blade to the motor housing from time to time. It's quick, easy, and works. On the other hand, the grounding schemes already suggested do make sense and I probably will try one of them soon. I have a couple of variations in mind and will post them if they work out. Thanks.
 
fitzo said:
Spray the back of new belts with an anti-static spray for fabric like Static Guard. Works well.
While it doesn't protect against static, it never hurts to ground your motor casings to an earth ground.
Click to expand...

The ONLY ground to earth should be at the main service entry.

Al P.
 
Mike and Scott thanks i will do that. I ve been getting very bad shocks and it can be dangerous when you jump.
 
I was also getting terrible static shocks from my grizzly grinder. After checking that there were no shorts in the system I ran a small wire from the grinding platten to the motor body, no more static.
 
Static electicity is exactly that - static electricity - meaning it is electricity that isn't moving because it has no place to go. So, if static is building up on your grinder, it is because it can't escape. Everybody else has already hit on the solution - ground the housing, which has nothing to do with the actual ground of the electric motor. A simple wire from one of the mounting bolts to ground should work. That's assuming it is the machine building up electricity and not you.


Oh, by the way, I'm not an electrician, but I did stay at a holiday inn last night.
 
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