Use a throttle to change the PM42's Option Switches 01, 02 and 09 as detailed in the PM42 instruction manual.
The PM42's trip current threshold can be set at a value from 1.5amps to 12 amps. Always use the lowest possible setting, consistent with good operation and reliable short circuit detection and recovery. Higher current settings are not "better." We ship the PM42 with a moderate current trip threshold of 3amps so it will work on most DCC boosters and layouts with no changes.
This is because some boosters cannot supply enough current with the track feeder resistance to reliably allow short circuit detection. If this is the case with your booster, you will have to run with lower trip current levels and fewer locomotives or upgrade the track bus and feeder wiring for lower resistance.
Always be sure that the PM42 reliably detects a track short at the track furthest from it and be sure the PM42 operates before the booster shuts down. Use the "quarter test" to create a short circuit on the track at the furthest point from the PM42 to be sure of this.
Note that sometimes overlapped and recurring faults from multiple sources may still trip the Booster short circuit protection (Digitrax Boosters beep 5 times at this point!), even though the PM42s are operating properly. This is unlikely, but can occur depending on the decision and fault recovery logic used by the booster. The PM42 generally should operate slightly faster than the Booster.