Quote:
Originally Posted by Don Rotolo
Of course, teams do have that 120A main breaker to limit the actual currents to somewhat lower values on a competition robot.
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Not necessarily. If you look at the current vs time curves for the breaker, you can draw significantly more than 120A sustained. I haven't seen the breaker's curve in a year, so I won't falsely quote specifics on it.
If you look at PTC curves (which I spent
way too much time looking at a month ago), a X amp PTC is spec-ed as "Never trip at under X amps, guaranteed to trip eventually at 2X amps". Pulse currents can be several times X. When you do the full tolerance stack up, you really need a 3x margin between the normal operational current and the fault current with a PTC.
Breakers require less margin, as they have better tolerances. Thermal breakers still have huge time effects, but some breakers use magnetic effects to counteract this.