This morning I was in a soon-to-be parking lot reparing some 2" pipes the asphalt company's grader had mangled. The 2" sweeps were buried about 3 feet deep so my coworker and I dug them up and were using a borrowed Rigid shop-vac to clean out the mounds of fill dirt and concrete dust that had clogged the first few feet of the pipe. To get past the bend of the sweep we duct-taped a three foot length of 1" pvc to the end of the shop vac's hose, and then duct taped about 2" of 3/4" smurf tube on the end of the 1" pvc and were poking it in like a giant aardvark's snout down the sweep to get the dirt out. I was standing outside the hole, and my co-worker was in the hole on his knees, hunched over the pipes while the shop-vac did its work. Suddenly his shoulders jerked the way your body jerks when you touch a live wire. I shut the shop-vac off and he told me he just got shocked and saw a five inch electrical arc inside the sweep between the wall of the sweep and the 1" pvc pipe stuck down it (it was about 7:45 am, broad daylight). He said, "you take a turn", so I got in the hole and continued on with the vacuuming. The shop vac hose was hanging right next to my arm, and after about 5 seconds all the hair on my arm started to stand on end. Shut the vac off, my hair lies down.. Turn it on, hair stands right back up. I never got my shock or 5" arc, but thought it was kind of interesting that a shop vac could build up that much static charge. The weather wasn't particularly dry and the soil was damp. My guess is that the dry cement powder filling the pipe might have helped things, but still, a first for me.
A GC that i work with had experienced the same thing. They were getting pretty good shocks from the plastic hose of the shop vac. They told me to try and i said i will take your word for it. Their solution was to twist #14 copper on the PLASTIC hose and bond it to a near by grounded item. Faucet, building steel, frame of an appliance. This bonding of Plastic hose to a grounded surface made it easier for them to work.
I thought it must be a static charge. But how come it does get build up when one does regular vaccuming.
Be kind to your neighbor, he knows where you live
#72974 - 12/13/0610:36 PMRe: static charge and shop vacs
Try sucking up toner beads. That is really a static machine. We had to use special conductive tools and hoses. You can go over on the woodworker's BB and read about tricks they use to ground their dust collectors. They worry about explosions
#72977 - 12/13/0611:50 PMRe: static charge and shop vacs
Had a related experience one time while we were involved in a manufacturing area retrofit. It was a 60,000 sq. ft. room with precast walls and bar joist type roof support system. They were making some changes to the concrete floor and were running a mini excavator and a skid loader inside. Because the area was enclosed they asked us if we could run some large process related exhaust fans to draw the fumes out. These babies were big and produced about eight air changes per hour. As soon as we started the big fans all of the trades that were working on hi-lifts began to complain about getting very nasty shocks when they touched a bar joist. They all started touching it first with a piece of ready rod to discharge the static charge . A couple of days later when we the concrete work was finished and we shut the fans off this problem went away. From what I understand about static electricity I think that this was caused by friction. Friction can be caused by air molecules moving over a surface, even in a 60,000 sq. ft. room. In fact, isn't this how lightning develops?
#72981 - 12/14/0602:46 PMRe: static charge and shop vacs