Saturday I was in the shop using the Harbor Freight blast cabinet to clean Vette parts. It had not warmed up yet so I was wearing a flannel shirt, with a sweatshirt over that. After a while, as I'm leaning against the cabinet, I realize I'n getting shocks in each upper arm, where it hits the side of the cabinet! Fortunately I didn't have bare arms touching it.

OK, the darn light inside the cabinet must have a short, so I unplugged the adapter, and put in one of those HF freebie lights, with a whole bunch of LED's. In the back of my head I'm a little surprised it put out enough juice to zap me but oh well. I resumed work - and I'm STILL getting shocks! Finally put a couple of 2x4's on the concrete floor and stood on those, and had no further problem. Put the cabinet light back on and still no shocks.

There are NO wires going to the blast cabinet. There is the rubber hose for the air inlet, and there is the plastic shop-vac hose to suck out the dust. Obviously neither of those is live. Am I right in thinking the blasting generated static electricity? Ive used the cabinet probably 15 - 20 times since I got it and never had this issue. If it matters, I'm shooting 80-grit glass bead media.

In the floor of the shop a couple feet away, there is a piece of threaded rod embedded in the concrete where a previous owner had a compressor anchored. I'm thinking of taking a wire from some metal screw or other in the cabinet, and running it to that stud for a ground.

Anybody else encounter this? Any other ideas or suggestions? Thanks!

 

This is the first entry from a Google search: Article

 

I've gotten zapped doing the same thing, so you are not alone. Static electricity.

 

Static Electricity due to dry air and friction created thereof. A ground to the rod in the floor may or may not cure the problem. You need a ground rod to ground the cabinet to. You can probably drive a ground rod outside in the ground and run a wire to it. I don't know the soil moisture conditions or other data in your area to recommend a depth for a ground rod. It is easier just to buy a rubber mat to stand on.

 

Wrap a flexible wire around the outside of the nozzle hose,a nd securely attached to the metal air gun and cabinet. It will eliminate about 90% of the static.
Doug

 

(from the article Kellsdad linked to).

I had not thought about that aspect.

 

Basically anything metal that the air passes through or contacts must be grounded to minimize static electricity.

 

I do a lot of media blasting and encounter the static shocks but I consider it a reminder for my heart to continue to beat.

 

 

 

Yep, it's static electricity. I always get zapped when using the sand blaster or polishing metal with the buffing wheel on one side of my bench grinder.

 

Yup, I'm constantly reminded of how much I DON'T know!

 

I also get zapped while buffing. I now keep a finger on the buffer so the static wont build up. Now my hair stands straight up!

Dom

 

I use one of my wife's old fake gold chains hung around my neck with a jumper wire from it to the cabinet.

 

As was mentioned previously, the static electricity is from the air and media running through the gun. Run a stranded wire (so it won't break from flexing) from the gun (attached to a screw or metal portion of the gun) to a handy screw on the cabinet. I taped my wire to the delivery hose to keep it out of the way. You are then providing a path from the gun (where the static electrical buildup is) to the cabinet which should be grounded with the light power cord. The shocks that are experienced are coming from the static charge buildup at the gun, and you are providing a discharge path (becoming part of the discharge circuit) by touching the gun with your hand, and the metal cabinet. Running a wire provides a path for the static electricity that is an easier path for the current to follow than your arm. Even if your cabinet is not grounded, the current is trying to get to the cabinet, hence the shock. You can ground the cabinet if desired, but I think you will find that running a wire will suffice.

 

Years ago I supervised an engine shop. New hires always started in head tear down and cleaning. We had a magneto hooked to the blasting cabinet. They would get lit up pretty good. This one guy keeps coming and telling me the cabinet is shocking him. I would grab it and say "see nothing". Then he would touch it and bam. First he got a pallet to stand on that didn't help. Then he grounded it to the conduit and stopped it. We gave him high marks for his many attempts to solve the problem. Then we put a piece of metal inside the glove and ran the wire through a finger tip. He got a hold of that metal and was pulling it out when they fired him up again. With his hand in the glove around the metal it was harder to let go of and get out. I guess you couldn't do that now days.

 

Nor would you rig up a hidden battery, trembler coil and a wet towel on the floor in front of a dorm toilet on a stupefied Saturday night, or would you?

Dan.

 

 

So you're saying the path was not from the cabinet, through me, to ground, but rather from the gun, through me, to the cabinet? That sounds quite logical, except that when I stood on the 2x4's the shocks ended.

The light probably is no help as a ground - not sure just what voltage but it has a transformer or whatever like a phone charger, and a very thin wire from that to the light. I'm guessing it's a very low voltage and the cord is not useful as a ground. And also I w as getting a zap both with, and without, the light being plugged in.

I'll try one step at a time. First I'll ground the cabinet and if that fails I'll try a wire from gun to cabinet. Or the other way around. I'm just glad it first happened when i had a couple layers on, instead of summer with care arms!

 

I doesn't hurt that bad.

I first noticed the phenomena when i was demonstrating a new technique for vacuum loading 50 lb bags of calcium carbonate into a 1000 gallon mix tank under the fluid level. (Tank was under a vacuum), using metal perforated wand attached to a 2" diameter flexible plastic hose with the wand stuck inside the bags of CaCO3. You could suck a bag empty in about 3-4 seconds
I felt my hair stand on end big time, and a customer reached out and touched my arm.

I felt a shock, but he called me all sorts of bad names and danced around after a 6"- 8" spark jumped from my arm to his finger. You probably know what a 3/4" spark from an 40KV ignition coil feels like....this was probably a 200KV spark

Wrapping a stainless steel multistrand ground wire from the wand to the metal valve on the tank stopped the problem.


Doug