Originally Posted by ewinterbee
So I opened my junction box where the trailer 7 way plug joins my fivers wiring. This was a used camper safety certified by a dealer from whom we bought it. I found two things puzzling in there. The first is the ground wiring. [B]I have a 10 gauge ground wire coming from the 7 way plug and a 10 gauge wiring going back to the battery (trailer wiring) and both of these wires are wire nut connected to a 4 ga ground wire going to the frame. The battery 8 feet downstream of this connection has a 2 ga wire going from battery ground terminal to the chassis. Common sense in my mind would indicate 2 10 gauge wires should be connected to a third 10 gauge wire going to frame. [/B]Before I do something stupid and change it, is there any logical reason I would need a 4 gauge ground wire instead of a 10 gauge? The wire nut connection of these three wires seems "fragile" and is probably only partially functioning at best! Second thing puzzling is an inline 10 amp fuse on the left brake light circuit. A quick test (pulled the fuse) reveals it is on the brake light circuit and not the electric brakes. I will do further circuit testing when I actually replace the 7 way plug. Any help or information that you can share would be greatly appreciated.
My apologies in advance if I am misreading the post.
10 gauge, by estimation, is good for about 30 amps at a run of 8 feet. 4 gauge, by estimation, is good for 125 amps at 8 feet. So theoretically, yes, you need 4 gauge wire or a gauge that can at least handle 60 amps plus a safety factor to ground to the chassis. The larger the gauge, the safer the wire is from burning up.
So in his case, using the theoretical numbers listed above, if you used all 10 gauge wire, you could be sending 60 amps through a 10 gauge wire that can only handle 30 amps and theoretically having your wire burn up.
I like to use the water pipe analogy. If you have 2 feeder pipes carrying water to a junction, the outflow pipe has to be twice the capacity of the feeder pipes or the water system won't flow at the speed of the two feeder pipes.
As to the battery 2 gauge negative, there may be other wires grounded to the chassis that necessitated a larger gauge wire. Too big is great, too small is dangerous.