Thanks all. Especially to solarpowered for his constructive comment.
A little background. The cooktop unit has been in place for several years and it's in good shape. The cooktop is a standard indoor one, and it's very well sheltered from exposure to rain or dew. Given that the location gets no snow, I'm not sure that the cook top is going to see much more moisture exposure than in an indoor kitchen, with a sloppy cook.
The unit is hard-wired, on a dedicated 4-wire branch circuit (i.e., has an EGC). If there is leakage current, the EGC will do what it is designed to do, and the cooktop housing will remain at zero potential. I do suspect that there may be some leakage current, which was behind my thought to not GFI-protect it.
Most old indoor electric ranges probably have some leakage current. Thanks, Trumpy, for your constructive input on that point. If I recall right, your RCDs trip at 30-40 mA, right? With leakage, the frame of the range stays at zero volts because the grounding conductor provides a path of (close to) zero impedance back to the source. No need for GFI protection.
Thanks to your comments, I realize that the outdoor setting makes things different. FYI, I am going to recommend that the unit be put on a GFI breaker, mainly because of the cooktop listing issue (i.e., it wasn't designed to be used outdoors). If the GFI doesn't hold, I may make some measurements of current on the EGC, just to see how much. At that point, it'll be the owners choice to disconnect or replace the grill.
Cheers,
Cliff
