This invention relates to a residual current device which is able to safely and reliably operate when a line voltage is present and when the line voltage is not present or falls below a predetermined threshold level. Each channel in a parallel bus can be populated in a matrix, with each row comprising ideal voltage values for the channel, and the columns comprising bits of the sequence of voltage values for that channel. The two supply units are disposed vertically outside of the transfer chamber and between the two processing chambers. In some cases, more than one \u201cshell\u201d region may be present. The adjustment means is coupled to the support means, and the attachment means is connected to the adjustment means.