There are only two circuits in the area. They are split down the middle. So the area that is acting up is circuit 3, area for circuit 3 is 2 sections of 18 lights. Circuit 1 is working fine but once we get to that first area of circuit three we have this problem.. so what i mean by extention cord is we havent pulled in permanent wiring yet so we are testing the lights. There are 4 rows of 18 lights we test. We plug in an extention cord to 20 amp recep in the trailer. Which happens to be shared wit a mini fridge. And take the cut femal of an extention cord and pigtail it to the hot and neutral allowing us to get the lights tested
It sounds to me like you have 72 fixtures all together, four groups of 18, and that you're putting two groups on each circuit?
Three of these groups are acting fine, and one group is tripping the breaker?
If you're using the same extension cord plugged into the same receptacle to test all four of these, and all of your groups are the same quantity of 18, then it's not an overload.
If you were to add together the length of your circuit to that receptacle, the length of your extension cord, and the length of wire connecting all of the lighting in that group, are you looking at 200-250 feet, or more?
I still think you have a dead short somewhere. And the length of wire you have before you get there he's adding enough resistance to make it act like an overload.
Break that group of 18 in half, and hook up 9 and try that and then hook up the other nine and try that. if one group of nine works okay and the other group of nine trips the breaker, then you need to be looking for a short. Maybe a conductor nicked inside an MC cable, or a fixture wire pinched