electrical wire thru concrete wall

Hot tubs have lots of very special requirements.

http://www.selfhelpandmore.com/homewiringusa/2002/accessory/hottub/index.htm

One of which is that it needs an insulated ground wire, not bare.

That means that you need to run conduit.

thank you bill hart does the conduit have to be metal or plastic??

Most homeowners find plastic much easier to work with.

Assuming that the hot tub will be outdoors, as long as your cable is in the interior of a one family dwelling, you can run the 6-3 cable and transition it to a plastic raceway by putting in a junction box just before you penetrate the wall. You will have to make splices in the box and continue with wire that is rated for a wet location such as THWN. If your work will be inspected, check with your inspector. Some of them do not object to the 6-3 penetrating the exterior wall provided that it goes into the back of the required disconnecting means.