Shocking! Shop Vac

[Ishmel]

Hey all, I have a question about my shop vac. It is a 4.5hp 16 gallon with a 1 1/4" hose that I've had for about 5 years. I've noticed lately that if the hose is touching me when I'm using it, then I in turn touch something metal, I get a h*ll of a shock. Could I have a short somewhere in the system, or is this most likely static buildup? I seriously think it's static, but I want to be on the safe side if anyone else has had this experience. Also, if it is static... Is there some way to "ground" the hose so I don't get zapped so often? I've had a couple of pretty painful shocks.

Thanks!

d

[LarryG]

Danger, Will Robinson!

The symptoms sound much more like an electrical or grounding problem than static electricity. A static shock will zap you once as it discharges and that's it. If you're feeling a continuous shock, sort of a vibrating sensation, that's a dangerous situation that must be corrected immediately.

The reason you feel the shock when you touch metal is because you're providing the current with the shortest path to ground ... hence the danger.

You should be able to test the theory by plugging the vac into a ground-fault protected outlet. If it's a grounding problem, which I'm virtually certain it is, the circuit will trip as soon as you turn the vac on.

[LCHIEN]

could be static or not.
Static would dissipate pretty fast whereas an electrical short would continue shocking you but it sounds like you can't hold it so it shoulds more like a short. I'm not encouraging you to hold it!

You probably should take a volt-meter and check for continuity between the exposed metal on the hose (is there any?) and either of the prongs on the cord. and if it has a ground between either of the power prongs and the ground prong on the power cord. IF there is continuity, You got a short. Don't forget to turn on the power switch (unit unplugged) when you make this test.

[djmst38]

shop vac

This happens to me all the time. It gets worse if it is dry weather. I had it attached to my planer once and I walked by the hose and it actually arced and zapped me in the leg so hard I felt it for days. It is difficult to ground a plastic hose.

[Ishmel]

Whoops, I should have clarified. It's more of a "discharge" shock. Big blast, no amps type shock. NOT a continuous shock. I think that it's static buildup, but I can't understand how it could build up that much static, plus it hurts! The hose is plastic, so I'm not sure how I would check continuity.

Thanks!

[jackellis]

This was discussed in a woodworking class given by a friend of ours who knows his stuff. There is some potential for static buildup, and if that's your problem, you need to ground the hoses immediately because static electricity + dust = explosion hazard! (Think grain elevators).

I believe some DC hose comes with copper or aluminum wire embedded in the walls but exposed on the inside. Perhaps running bare copper wire on the inside and attaching it to a grounded chunk of metal will help.

[just4funsies]

It HAS to be static, because he says he gets it when grounding himself and touching THE HOSE. There are (usually) no wires or metallic parts in the hose to bring AC current to him from the electrified parts in the shop-vac (i.e. motor, switch, power cable, etc.). Only other way it could happen from contact with the hose would be if the hose was wet, and continuity was established to a current source.

[Tom Miller]

I guess we're coming around to the consensus that you're experiencing a static shock. Another very easy way to test is to block the flow of air with the vac on (e.g., with your hand over the end of the hose), and you'll probably notice there's no shock.

A grounding wire would only help if the hose was somewhat conductive. It won't really reduce charge from the hose, otherwise, as that plastic can maintain a pretty large potential difference.

If your hand is in contact with that grounding wire, though, it might keep the magnitude of the shock down.

Regards,
Tom

[mckinneymesa]

here in arizona where the humidity level is below 10% most of the time, this happens to me all the time when i'm cleaning up after creating a mess. if you have a good answer as to how we can clean up without getting a static discharge all the time please tell us. i think its the dust passing thru the hose that helps build up the static. like when we were kids dragging our leather shoes on the carpet to build up a charge and zap someone.

[LarryG]

It HAS to be static, because he says he gets it when grounding himself and touching THE HOSE.

Some hoses are reinforced with wire, which is what I was ASSuME-ing when I composed my initial reply. But yeah, given the additional info, it does sound like static electricity.

[LCHIEN]

Some hoses are reinforced with wire, which is what I was ASSuME-ing when I composed my initial reply. But yeah, given the additional info, it does sound like static electricity.

I was sort of thinking he had an older unit with wire-reinforced hose, too, which is why I suggested checking continuity to metal in the hose.

I've seen a number of articles debunking this explosion myth including an expisode of Mythbusters. While dust + spark can = explosion the woodworking dust levels are not right and the energy of the shock on plastic pipe is too low. Lots of volts but not enough power.

The issue of personal shock is still valid. The situation is this, air flowing in the tube creates friction and attracts a charge on the outside of the hose. The charge persists because it has no path to bleed off, but while the voltage is high the amperage is low because the plastic cannot hold a lot of charge (no conducting surface like a capacitor).

If the hose were covered with metal foil inside and out but isolated (not grounded) then it would build up a huge charge and deliver a lot of current.

In order to minimize the shock it is necessary to have a resistive path to bleed off the charge. One way would be to mix some conductive graphite into the hose but its way too late for that.

The next way is to wrap the hose with conductive foil and assure that at least one end is grounded.

somewhere in the middle of effectiveness would be to wrap the hose witha spiral bare wire grounded at one or both ends. This would serve to carry charge to ground if the charge were sufficient to "jump" to the wire.

[Ishmel]

Thanks for all the good information. It sounds like most would confim my initial idea that it's static buildup giving me a shock. As for explosions, I grew up in a farming town in rural Minnesota, and spent some time at the local grain elevator (where the types of explosions you're talking about have happened) and my understanding is that the air has to be almost SATURATED with with dust, as well as under pressure and high heat. My shop get's dusty, and I can get pretty steamed when things don't go right, but I don't think the saturation or pressure is there for explosive conditions.

So now I have to figure out how to discharge that static from my shop vac hose. I like the idea of a grounded coil around the hose. Do you think I could make this from thin copper wire? What would be the most efficient way to ground it? I'd like to stay portable if I can. Do I need to actually ground it to a stake in the dirt, or do you think I could just attach it to something that I'm not touching? By wrapping a wire around the hose, am I increasing the capacity of the hose to hold a charge and risking a bigger shock if it's not properly grounded?

Thanks again!

d

[just4funsies]

It would have to be grounded to a cold water pipe or other reliable ground source (such as the 3rd slot in a grounded outlet). You could use a large alligator clip (like those found on a battery charger, for instance. There's no place to ground in the shop-vac itself, unless it has a 3-wire cord (most don't).

[Bruce Cohen]

My Craftsman used to do that to me, Great way to start the day.

One day it stopped and never came back.

I think I miss the jolts.

Bruce