maybe I explained it not in enough details. On the slab I have glued engineered hardwood (1/2"), then I'm putting cement boards on thinset (so other 3/4"), and then tile it.

I thought to put the wires either between the boards, or even make a groove in the hardwood for the wires.

Does it still mean I have to use conduit under tiles and in the island?

Not withstanding the electrical problems, this sounds like a flooring disaster waiting to happen. You might want to run this by in the flooring forum first.

You can't do what you want with the wiring (either suggestion).

The proper way to do this would be to remove the previous finish floor, cut a channel in the slab and install conduit.

:-) thanks for pointing it out.

Why do you think I can't do it? the total thickness allows to put conduit even without cutting a channel in slab. why you think I should remove flooring for laying conduit?

I presume, dangerous thing to do, you are getting a permit for the wiring. If so, I would run your ideas through your local inspection folks. There is also the possibility that a careless floorer might run a nail through it.

It seems to me that if you can get the conduit fully under the cement board--in a channel between boards (whether you need to cut a channel or not) would be sufficient and won't create a flooring problem. The cement board will be able to span a 3/4" or 1" gap. If neecessary you could put some sort of filler around the conduit so there's no gap.

romanr: tile guys will not warm to this Idea well. Leaves a heck of joint to try and mud (you know the cement board joints must be mudded with thinset and akali resitant mesh tape and that thinset must be placed under the CBU?)

Heimert: cement board has no structural value assigned to it so it should not be bridging and gaps.

The hardwood MUST be removed if you actually want your tile job to last beyond about 3 months and not be a waste of time and money. And, the slab MUST be channeled into in order to properly route electricity to the island. This isn't a job in which to cut corners.

I heard the opinion that hardwood must be removed. Although an alternative option was backed up by a few contractors. The logic for leaving the hardwood was:
- it's glued, not floating or nailed so not moving;
- in this fashion it's similar to plywood floor;
- screwed hardboards (and two thinsets) will secure tiles from potential hardwood deformations;

Does it sound logical or you think deformations/movements can be so strong that they will go through the cement hardboards and push tiles?

The problem is it does not have the same strength as plywood plus plywood used in a tile job must have an exposure 1 rating meaning outdoor adhesive is used in its manufacture. On the flooring forum look for a guy named bill Vincent, he is an experienced tile setter.

IF I did tile over hardwood I would likely use an uncoupling membrane such as ditra.