you need 8/3 with ground (two hots, neutral and ground) to properly install the cooktop.

NEC specifies following manufacturer's instructions

Hi
Thanks
Do i need to rewire to the main ( crazy task), or run the ground from cooktop outside to a 8ft pole? Neutral/white would be connected to ground for 8/3 back to breaker box...

I think it has to go from the main because as it is now there is no neutral. The neutral may not be a bare (or green) wire.
Also the 8 ft ground rods are for panels and are usually supplemental.

Read rod instead of pole..

Not sure about the significance of your picture, but your 8/3 cable has two hot wires (red and black) which go to the 40A double breaker which in the pic I assume is in the "off" position. We can't see where the neutral (white) wire goes, but it should go to the neutral bus bar which is in the upper left part of the panel. You should also have a ground (bare copper) wire which runs to either the neutral bus or the ground bus. The ground and neutral busses are bonded together in the panel. That's the only safe way to hook up the 8/3 in your panel. At the cooktop receptacle, the red and black go to either of the two line connections, the white goes to the neutral, and the bare copper first loops under the ground screw in the 4 11/16" box and then to the ground lug of the receptacle. If you don't have 8/3 wire as described, then you'll have to re-wire. Do not connect the white wire to ground if you only have 8/2.

Hi
Well I was confused certainly .The wire which goes to the cooktop looks like 8/2 with ground ( red/black/bare)...pic
So there is no neutral it seems going to the cooktop.
http://photos1.blogger.com/x/blogger/4675/2055/640/856491/P1010011.jpg
Good lesson... I should have asked before buying this cooktop. Going to be pretty crazy to bring a wire from the garage to kitchen
Thanks
JF
http://photos1.blogger.com/x/blogger/4675/2055/640/235998/P1010021.jpg

Well if it is existing wire from years ago when the code allowed it, you can bond the ground of the cooktop to the neutral white wire. If the wire is only 8/2 with ground, it never was code for a 120/240 appliance and it must be re-wired. You can not connect the white of the cooktop to the green or bare wire. If the cable has red, black, and white and is already there, you should be able to use it and the white is both the neutral and the grounding conductor.

There is no neutral/wire at junction box.Could the ground coming from main used as neutral?

No it sure can't this is a problem that many people violate an it is dangerous. I take it you are a contractor. Do the correct thing and wire 8/3 with ground from the panel to the cooktop, just bill the customer for your time or an electricians. Using the grounding wire as a neutral would be dangerous as it would be using the bare wire as a current carrying conductor. Electricians are suppose to be able to assume that the removal of a ground wire (while working in a panel) won't possibly kill them. Even if the cable had a white with no ground it would still be dangerous although allowed. If the white came loose in the panel, the entire chasis of the appliance would become a hot wire waiting to electrocute the next person that touches it allowing the componets that use the neutral to turn on. What you have there (black, white, and bare) is good for 240 only and not 120/240

I am not in the business at all. Installed the cooktop this afternoon in my kitchen and was doing my homework on the internet before connecting the wires.I will contact an electrician now cause this job is out of my knowledge.
Thanks again!
JF

Oh ok just got from the "I am supposed to install" guess that is just your own suppose to :) Yeah it will be a great thing to have this done correctly.