good luck, i'd be just happy to find the stud(s) for the shelving.who knows what else zircon picking up.don't use too long screws just in case. if you find a stud, your chances of hitting a hot wire is very rare.
unless your kitchen is next to a outlet jungle.

wear rubber gloves...ZAAAP!!!!

When the wire pass through a stud, do the studFinder detect the wire outside the stud or inside the stud?

fOR the residential, I assume my house used wood stud. I wonder what is the normal stud size, 1"for stud width? For chicago area, do the contractors use 16" O.C. or "24" O.C spacing?

Studs are usually 1 1/2" wide.
They will typically be at 16" oc - but there will of course be deviations in the pattern (extra studs or different spacing) if there are windows, doorways, and sometimes if there's been previous remodeling involving that wall.
If your kitchen was originally designed as a kitchen, and if you're putting the shelf at a "typical" height, you may find that there are one or two rows of continuous blocking in your wall - because a lot of residential contractors do this as a matter of course in wall in which it's foreseeable that someone will want to put cabinets at some point.

If there is a wire running horizontally in your wall then it has to pass through the studs. Your stud finder should be able to detect a wire in or out of a stud - but these gadgets are often over-sensitive, meaning it may warn you of a wire when it is several inches away from one in either direction. They also sometimes give false readings about "wires" when what's really there is a pipe.

everything in chicago is in conduit and you should be able to visualize the conduit routing. most likely the conduit aligns with the centerline of the outlets above the cabinets. if your house is cmu most developers cheapen out and just put furring strips on the wall and would be 24"[with energy code they have to put insulation in the wall]

if your putting lag bolts or expansion bolts to hold up the shelf, just cut the power to all devices in the kitchen and go for it. if for some ungodly reason you hit a live wire, you blow the circuit thats all.[perhaps a bit more if you hit that convection oven 220v outlet.

I’m not familiar with the capabilities of Zircon’s stud finders as far as finding open circuits. Another lifetime ago I was working in building maintenance and we had some pretty cool circuit testers that could find and trace specific runs.

These days I have a simple $5 device from Home Depot called Circuit Alert and it is made by GB Instruments. Press the button and touch it to a shielded wire and it will tell you if it is hot. You can also drag it along a wall to follow a live circuit.

I would go out and get one of these, turn on all the lights and run it across the wall you are worried about drilling into. But the chances of sinking a drill bit into an open circuit are pretty slim.