The reason that we need to ground a slab is that we want the entire concrete slab to act at, or be at the same potential as the earth. We’re essentially bonding the earth and the slab together so that they are “the same thing.” The theory behind this, we will get into at great depth much later, but for now just understand that all of those pieces of rebar are being connected together with a large grounding electrode conductor that we extend out of the slab and will put in our electrical service once we build it later.
The national electrical code defines certain methods in which we can achieve this but one of the most common is to take a conductor that is sized per NEC table blah blah blah and lay it in the concrete beam with the rebar. We also need to bond this conductor with a clamp to the rebar so the conductor is actually touching, And permanently connected to the rebar. This ensures that the conductor we are laying in the beam is at the same potential as the rebar in the slab Dash essentially making them all one gigantic conductor.
once you’ve gotten the grounding electrode conductor clamped to the rebar run the remaining out to the service location and leave yourself enough length to get up inside of a service panel. A good practice is to use some sort of raceway or conduit to protect this conductor as it emerges from the slab once it’s been poured. The NEC blah blah blah says you have to protect this conductor From damage.
Sizing the GEC
how do we know what size conductor this must be? Well until you really get your grips about you and know what you’re doing at your master electrician or journeyman is going to be deciding this. But so you understand the importance that this conductor has it must be sized to the national electrical code. We use table blah blah blah and bass the size of this conductor on the size of the service. So for example if we have a 200 amp service this conductor must be number six copper, or if we have a 400 amp service the conductor must be 1/0 copper.