1 m sec there are three modes of output selected by the option input 29 34 op 34 to the logic and also by the method of connection of the mains trigger zero crossing detect inputs the first mode is 4 wire single pulse the 4 wire connection is shown in fig3 in which the input and output mains are the same option input 29 is set to logic 34 0 34 34 op 34 is high and the input and output zero crossing detectors are connected together so that mt1 mt4 mt2 mt5 mt3 mt6 the output logic 34 1 34 then consists of a single 1 m sec pulse of 120 khz starting immediately after the zero crossing of each pulse with respect to neutral this mode would be used for a normal 3 phase 4 wire system where the 208 v type of operation is not required a second mode is the 4 wire double pulse option input 29 is set to logic 34 1 34 34 op 34 is low and the output zero crossing detector gating signals g4 to g6 are not used by the logic the output logic 34 1 34 consists in this case of two 1 m sec bursts of 120 khz on each phase fig2 the first bursts begins immediately after the zero.