Not sure what a three pole circuit breaker is. The way you have worded this suggests you are referring to 3-phase circuits. If so, a consumer unit doesn't normally have a 3-phase supply to it unless you have a workshop or an industrial supply. A domestic supply to a single dwelling is one phase of the 3-phase supply that is distributed along the highway. You put a circuit breaker in that supply between the incoming live cable and the domestic load. The neutral goes back from the return side of the domestic load to the cable in the street. What exactly are you seeking to do?