MTcummins
In the Trades
quote; if you leave a pocket under there, the slab support will be compromised and you could get slab cracking
You are underestimating the strength of concrete. I had to break into the floor of a supermarket once, and the ENTIRE subsoil had settled 18" so the entire floor was being supported by the foundations for the roof columns, and it was NOT cracking even with the public traffic through the store. In many cases, residential floors already have a void under them, which makes it easier to break a hole in the floor. You definitely want a conduit for the wires, if for no other reason than future changes in the island.
If you want to do that to your house, go for it... I wouldn't leave a void under my concrete (and my concrete is only in the basement with no finishes on top of it). It MAY not crack, but you are significantly increasing the chance that it will. Just because voids happen doesn't mean you should do it intentionally. Pretty sure the code officials would have something to say about that, with how particular they are about proper prep after busting out a slab to run lines underneath.
If this were me, I'd get a diamond blade for your circ saw, cut a trench about 2" wide, drop the wire down in there in conduit, and fill the void. It really wouldn't be that bad... you'll spend a little more money on parts, but you'll be done much faster with a better install than trying to fish under the slab. On that short of a trench, I'd not be overly concerned about the strength of the slab being compromised, unless of course it is a tensioned slab... but that wouldn't be too common unless you're in a large building.