Concrete flooring are most frequently grounded. Concrete at grade level is always believed to be at ground potential because it absorbs moisture from the earth and is an excellent conductor in direct contact with the earth. For this reason, any electrical wiring or cables that pass through a concrete basement floor must be protected by conduit or cable armor. Concrete above grade level does not have to be grounded. The current belief is that if you're not going up into the attic, then you don't need to ground the house. The only time this isn't true is if there are metal panels in the ceiling containing electrical wiring or heating/air-conditioning ducts. In this case, the metal in these panels will not conduct electricity and therefore they do not need to be connected to your circuit breaker panel. The best way to tell if concrete floors require grounding is to call an electrician and ask him or her. Some concrete floor manufacturers will label their products as requiring grounding, while others do not. If it's not labeled, then you can assume that it needs to be grounded. The second way to tell if concrete floors require grounding is to check with your local building code department. Most cities require concrete floors in basements to be grounded for safety reasons.