Strange shock from vacuum

[danickstr]

On a job recently, the drywall taper told me that his vacuum shocked him every time he turned it off. I was intrigued and took it apart. After a bit of poking around, I found that the ground wire was draped across the lead closest to the motor winding, but its casing was intact.

After thinking about it a bit, I decided that the field collapse from the motor must have been strong enough to throw its impedance through the ground's jacket and send a bit of the collapsing amperage at him.

I kind of laughed to myself that the wire had jostled itself to that spot. But I also marvelled a bit at the power of a collapsing motor field.

 

[bjp_ne_elec]

Did you check to see if the case of the switch was hot? I could have an internal short. I doubt if it was the collapsing field. And it wouldn't be an "impedance through the ground's jacket" - if anything it would be an induced voltage. Impedance is resistance, not potential.

 

[ultramegabob]

does your jobsite have GFCI protected recepts for the workers? Im pretty sure that is an OSHA requirement, if there is GFCI protection, it sounds like it needs checked out....

 

[sgunsel]

Ruling out bad wiring, sucking up drywall dust can create a significant static charge - enough to be painful with a shop vac. The dust particles collide with the walls of the pickup tube and hose to generate static electrical charge. The higher the velocity, the more vigorous the charging. The typical wet-dry vacs that I have used are well insulated and have double insulated motors. With non-conductive hose and tank, and in dry air conditions, very long sparks (very high voltage) can be produced. If the vac is charged and the operator is at a different potential, which is very likely, it can be unpleasant.

 

[hockeyoligist2]

Ruling out bad wiring, sucking up drywall dust can create a significant static charge - enough to be painful with a shop vac. The dust particles collide with the walls of the pickup tube and hose to generate static electrical charge. The higher the velocity, the more vigorous the charging. The typical wet-dry vacs that I have used are well insulated and have double insulated motors. With non-conductive hose and tank, and in dry air conditions, very long sparks (very high voltage) can be produced. If the vac is charged and the operator is at a different potential, which is very likely, it can be unpleasant.

Ditto, I have had that happen many times.