A simple but exact derivation of the conditions for ground potential on the null instrument input in nongrounded ac bridges is given. It is shown that not only the ``Wagner‐earth,'' but also other networks and circuits between the power source and the ac bridge can easily fulfill these conditions. Advantages of such other networks and circuits are discussed. General considerations for optimum bridge details for measurements of highest obtainable accuracy are given. Practical supply circuits for ac bridges are described. Furthermore, it is shown how the adjustment of the earth capacity neutralizing system can be made in a minimum amount of time.