The 3-phase, 3-wire pilot exciters on the SR4B Cat generators I work on only have two fuses instead of three. My understanding is if there's overcurrent on any one of the three phases, either one of the two fuses will blow, protecting the circuit. All complete electrical paths must flow through at least one fuse. A third fuse would be superfluous.
![Motor Branch Circuit Conductor Sizing [430.22(A)] (14min:30sec)](/img/1.gif)
The 3-phase, 3-wire pilot exciters on the SR4B Cat generators I work on only have two fuses instead of three. My understanding is if there's overcurrent on any one of the three phases, either one of the two fuses will blow, protecting the circuit. All complete electrical paths must flow through at least one fuse. A third fuse would be superfluous.