Recently, you've come across complaints from operators about a couple of drinking fountains in a production area. It turns out that similar complaints have been made for quite some time, but never resolved. The complaints range from a tingling sensation to a shock when taking a drink.

The complaint history doesn't show incidences of this problem in the summer months. The repair history repeatedly shows “unable to duplicate the problem.”

The fountains have been swapped with ones where the problem hasn't been reported, and the problem stays in the original location. Maintenance has conducted insulation resistance tests on the branch circuit wiring five times, and the results show nothing to indicate impending failure.

One theory is the operators are trying to amuse themselves by reporting a problem that doesn't exist. Could another theory explain what's going on? If so, what would it be and how do you investigate it?

The most likely explanation is you have something grounded where it should be bonded.

Article 100 of the NEC defines “grounding” as “connecting to the earth” (or to a conductive body). Article 100 defines “bonding” as “connected to establish electrical continuity and conductivity.”

Ground to dirt and bond to metal. On branch circuit equipment, you should be bonding instead of grounding. If you have this wrong, you get things like water fountain shocks. Bonding connects metallic parts electrically, preventing an accumulation of charge (potential) on any one part.

Some piece of equipment is building up a charge. Fountain operation completes a path (through the operator) that allows much of the charge to get back to the source (draw the circuit, apply Kirchhoff's Law).

In the summer, when people drink much more water, the frequent use of the fountain bleeds off enough charge to keep voltage below a threshold of detection via the skin. People are still conducting undesired current through their bodies; they just don't feel it.

Other fountains seem unaffected, which helps localize the culprit to something physically near those two fountains. Conduct a thorough bonding inspection, and you'll find it.