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Old 07-22-2021, 11:40 AM   #1
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4 ga ground strap in junction box?

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. 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. 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.
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Old 07-22-2021, 02:15 PM   #2
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Quote:
Originally Posted by ewinterbee View Post
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.
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Old 07-22-2021, 03:25 PM   #3
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Thank you for your reply. This is the 7 way towing light connector that plugs into the tow vehicle. There is a junction box halfway back to the camper where the 12v camper harness meets the 7 way plug wiring. We are not talking about the main ground for the camper electrical here. Here is how I see it and please, I am asking for help here understanding, so please don't take this as factual information, only my thought process and me asking for clarity. Left turn (brake light) at 1.75 amps. Right turn (brake light) at 1.75 amps. Taillamps Clearance at (estimate) 4 amps. Electric Brakes (variable) at 5 amps. 12v aux power feed at 10 amps. Reverse lights (low power l.e.d. fog) at 0.5 amps. If everything was on at the same time I would theoretically be using about 22 amps at 12 volts and in my head 10 gauge should be sufficient. That being said, it is the first time in 40 years of owning campers I have every seen a ground between the 7 pin connector and the battery. I dont see this ground to chassis here as even necessary at all because the system is grounded at the negative battery terminal. I view it as redundant. I will take pictures tonight and post them tomorrow to try and clarify. I am not new to electrical or doing my own wiring, but this is the first 5er I have ever owned and dont want to overlook something here.
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Old 07-22-2021, 04:55 PM   #4
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Welcome to the wonderful world of trying to figure out the wiring on your travel trailer. It's a whole new world where common sense does not always apply. It doesn't hurt to go through and clean up a lot of questionable splices and make sure everything is weather proof. Other than that if it all works then you're lucky.
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Old 07-23-2021, 09:59 AM   #5
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It's always good to have a heavy ground wire.
I'd worry more about the sketchy connections and what seems to be a misplaced fuse.
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Old 07-23-2021, 10:13 AM   #6
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This all started because I wanted to proactively replace the 7 way pigtail with a new one before we have a problem. The old one is showing 18 years (assume its original) of wear and expected this to be a slam dunk. Everything works fine and has since we got it. After seeing it, I have decided to also replace the box and clean up the rats nest of wiring thats in it. Due to working late last night I didnt get to the camper till after dark, so didnt take the time to open it and take photos last night. I will do that this weekend at camp and post them next week. I strongly agree that you can never have too many grounds. My big issue with this is a 4 ga and 2 10 ga in a "fragile" wire nut connection is probably less grounding power than 3 10 ga.
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Old 07-23-2021, 01:34 PM   #7
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If the connection needs to be stronger maybe the simplest thing would be to replace the wire nut with a ground lug.
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Old 07-23-2021, 01:52 PM   #8
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As I think about this, several ideas have occurred. First was just to eliminate and connect the 2 10 ga together. But as others have suggested, the more grounds the better. Then came screwing all three independent of each other to the metal box, then the metal box becomes the lug connecting them all. Another thought was a mini buss bar with 4 terminals that I could use to connect each to its own terminal to connect all together. But your idea looks better than the others I thought of. Thank you. Great idea.
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