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04-11-2023, 12:39 PM #21
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Don't forget that this pin 4 circuit may supply the power for your emergency breakaway braking system. If that fuse blows and you don't know it, your breakaway braking system may be inoperative. The chances of a problem are very, very small - blown fuse and RV separation incident at the same time - but the consequences could be catastrophic.
Rather than a fuse, one might use this: https://a.co/d/0oTPLCw.2021 Solitude 380FL-R
Ram 3500 MegaCab SB DRW
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04-11-2023, 05:05 PM #22
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Last edited by JPS350; 04-11-2023 at 05:09 PM.
2021 Imagine 22mle
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04-11-2023, 06:50 PM #23
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I'm not sure I understand what catastrophic failure the breaker wouldn't be fast enough to prevent or why the brake wouldn't work anyway. I might not have been clear. I didn't mean that the fuse BLOWS and the separation occurs AT THE SAME TIME. I meant that the fuse may blow sometime (minutes, days, or months) before the separation and then the separation occurs later, at the same time that you have a BLOWN fuse.
There are two concerns. One is preventing a fire from a short in the pin 4 charge wire. Either a fuse or an auto-reset breaker will serve that purpose. The second concern is not having an active breakaway braking circuit. If you have a fuse and get a short in that wire for any reason - chafing on the wire, a short in the hitch box where the 7-way cables are connected, or inadvertently shorting the pin in the RV plug - that fuse will blow and you might not know it. If the short happens while you are towing (most likely), you definitely wouldn't know the fuse blew. (Hmm, do these new HD trucks tell you if a fuse blows?) You are left with a dead breakaway circuit. How may RVers check the breakaway switch function every time they hookup to go? I don't.
At least with an auto-reset breaker, if you have a momentary short, the auto breaker will trip and reset, You won't have a fire and you will have an active breakaway circuit.
As I've followed this discussion along, I've thought that I might install an LED pilot light with a momentary pushbutton switch someplace on the hitch, with the + side of the LED connected to the + side of the breakaway switch. A quick push when I'm hitching up will confirm that I have power to the breakaway switch. Adding that to the hitching checklist would be a very minor addition to the process - 1 second or less.2021 Solitude 380FL-R
Ram 3500 MegaCab SB DRW
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04-11-2023, 09:48 PM #24
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A MRBF fuse is used for main battery protection from short to ground. An inline fuse can be used as well. Fuses are used for main battery protection, breakers are not. The reason is that fuses are fast and when they blow, you are safe. A breaker can fail, and it can also weld itself closed. I'm talking about protecting the main battery wiring. A short to the main power wire basically makes an arc welder until something gives. There really is no scenario where if your main power from the battery shorts that you could expect the break away to work, so the fuse is there to prevent a fire. If the fuse blows, nothing DC works in the trailer so it would be pretty obvious then.
Last edited by JPS350; 04-12-2023 at 07:32 PM.
2021 Imagine 22mle
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