independent functioning of the two core sections transformer 10 is a magnetic shunt transformer a type of transformer that limits the amount of current induced in one or more of its secondaries an alternate magnetic path is provided in parallel with each of the secondary sections when a secondary section saturates as it is designed to do at a predetermined current level the associated alternate path diverts any additional flux away from the saturated secondary as can be appreciated if one secondary section is saturated while the other is not the current limiting action will only take place in one secondary section this is why the secondary sections are shown as being parts of different cores secondary windings 14 are connected at one end to three parallel connected incandescent bulbs and at the other to solid state switch 35 which completes the bulb circuit solid state switch 35 can be any one of the many types commercially available a typical solid state switch might provide opto isolation by having the input circuit terminals 40 and 42 and led 38 connected only optically to the rest of the switch element 36 represents a gating circuit sensitive to light it gates triac 34 on.