A transformer is a device used to step a voltage up or down and isolate circuits. It consists of two sets of windings (lengths of coated wires), which have no electrical connection to each other. An AC voltage is applied to the primary winding, which generates a field of flux. This action causes the secondary of the transformer to generate a stepped-down AC voltage. In BUNN equipment, 12 volt and 24 volt step down transformers are most common.