I would look for a short on your layout.? Does the circuit breaker trip when the locos are crossing a switch?? Do your locos have sound?? If so, there's a current surge when charging the sound capacitors, so if one of the locos hits a dead spot and had to power up again that would be a surge.? Also do you have other locos on the layout with sound, they take power even if they aren't moving.
So look for shorts and dead spots, or just leave the setting at 3.5 amps.
Dan
