You didn’t specify what is happening when the short occurs. Do you only reset the breaker and magically everything works until next time? I agree with George that it is not the number of engines. I run mostly command equipment but do run a postwar F3 and MPC era GG1 and some other things with AC motors. Even with 5 lighted cars I have never seen more than 6-7 amps on my Z and I have never tripped the circuit breakers.
You don’t mention what you are running but I will venture a guess that, at least, one piece has an issue. It could be a bad motor or drive line, loose or frayed wires or something hitting the center rail. You are going to have to run each piece until you find the culprit.