What are the chances someone might touch the sink and the cooktop? Or the cooktop, and a grounded appliance? Or someone else touching one of those items? That parrelel path to ground from the current carrying surface of the cooktop posses a hazard.
Let me tell you of a service call horror story: I got a after-hours call from a resturaunt, where the dishwashers had reffused to work, and the manager only called to appease them.... I was about to leave when he told me that. Then tells me why - He said the dishwashers "claimed to be getting shocked from the sink." So I went back and finangled my best spanglish with the guy mopping the floor, who pointed to the sink and a metal counter. Then to the sink and another metal counter. 180 from one to the sink, 120 from the other, 240 to both. The garbage disposal was using the plumbing as a neutral, and the counters were installed with 3" screws that penetrated different circuits on each hot metal wall. I told the manager who didn't beleive me either, and refused to have me fix it. I asked one of the dishwashers how long it had been going on, he said years! (I called the boss who had me pull the breakers, and sharpie the hazard on the panel before I left. We called the city in the morning.)
So imagine this cooktop, and its "ground fault", any time your customer touches an appliance, or the sink, getting more than 5 milli-volts across their heart.
