Posted by David Sherman on Wednesday, February 08, 2006 at 3:11PM :
In Reply to: Shocking... posted by Chris Davis on Wednesday, February 08, 2006 at 1:59PM :
Make sure the cabinet truly has a real ground. Never assume the "ground" wire in any building outlet is really grounded. There are an infinite number of ways that "ground" hole in an outlet can end up not grounded. The most common is the amateur electrician who wired it simply didn't bother to hook a ground wire to the screw. Other common mistakes is they assume that since it's in a metal box attached to conduit, the conduit must be grounded, but in fact it is not, or the ground wire that was once connected from the panel to a water pipe is either no longer connected or the pipe is no longer connected because somebody put some plastic pipe or an insulated coupling somewhere in the line.
This method of ground testing isn't really kosher, but it's practical and effective: get a lighbulb socket with a couple of wires and a reasonably high-wattage (100 watt or so) light bulb. Stick one wire in the "hot" slot of your electric outlet (the narrower of the two slots), and touch the other wire to your blast cabinet. If it's solidly grounded, the lamp will light to full brightness. If it's not grounded, you've just put 120 volts on the blast cabinet and maybe your fridge and some of the other "grounded" appliances in your house at the same time. At that point, you need to find out why the "ground" system in your garage is not working.
Since you described a spark jumping to your face, you're right that the cause is static electricity building up, rather than 120 V power line leakage. 120 volts isn't enough to jump through the air at all. Obviously, metal parts should be solidly grounded.
If the spark is jumping from the metal part to you, either you or it is not grounded. The ground strap Kevin mentioned will ensure that you don't get charged up. On a concrete floor, wearing leather-soled shoes rather than rubber-soled ones is usually enough. The insulating mat Jerry described will only make matters worse. In general, static problems are worse in cold weather when the air is dry, than in warm or damp weather. If static is building up on insulating surfaces like plastic or glass parts, you can make them slightly conductive by applying something "hygroscopic" (absorbes water from the air) to them. In the electronics industry they have special "anti-static" products that do this, but slightly-diluted dish soap generally works fine. It doesn't take a lot of conductivity to make the static electricity leak off.
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