What Size Fuse is Right for Fuse Holder on Battery?

[Deleted User]

Hi, I wanted to see what size fuse is supposed to go in the fuse holder on my battery.  The red wire is 10awg and the yellow wire is 12awg.  I see some saying it needs a 20 amp fuse and other posts say 30amp fuse.  I know normally you use 20 amp fuse with 12 gauge wire, but since its such a short piece maybe 30 amp fuse is ok? I don't want this short piece of 12 gauge wire to be the weakest link.  Opinions? Thanks

Nomad

If you look in your converter box, the fuse there that's assigned to the battery is a 30 so the one at the battery should match - so, a 30

Tabaz

Replace that fuse holder and wire with a 10g wire with 30a fuse holder.  Looks like your dealer installed the wrong size.

Nomad

Another battery fuse discussion going on here...
 https://tab-rv.vanillacommunity.com/discussion/3137/blown-battery-fuse/p1

[Deleted User]

OutbackAZ that is exactly what I was thinking so happy to see your opinion matches mine.  I think I will do exactly that. I wonder why they would splice in a smaller gauge wire at the end????  I will check out the other thread also. 

ScottG

Good catch, robyn769.

Mine (2015 M@x-S) is set up exactly like yours: 12g fuse holder spliced to a 10g lead. In addition, the fine print on the fuse holder says "20A max" (a limitation based on the wire size, not the fuse holder itself). The fuse inside, however, is 30A.

I'm not certain, but I doubt it was the dealer who did this. I would expect the trailers to come from the factory with all wiring and ring terminals battery ready.

I'll probably correct mine at some point, but in the meantime I'm not losing any sleep over it. While the numbers may not jive, the likelihood that I will actually draw anything close to 20A off my battery at any one time is pretty small.

[Deleted User]

ScottG, happy to hear its not just mine that was wired incorrectly, but sorry to hear you also have this weird issue.  I also have a 2015 Max-S so it must be how they shipped them from the factory like you said.  Mine also came with a 30 amp but I switched it out with the 20amp when I saw the smaller gauge wiring.  Its a short piece but still, its now the weakest link in the system instead of the fuse as it should be.  I think I will leave the 20amp in there and see if it blows. It that becomes a problem I will switch out that section of the wiring.  I only use the battery for fridge power from home to the campsite, so I don't see why the 20amp would ever blow UNLESS there is a storm/power outage at the camp ground and I suddenly want to power other things.

ScottG

On a related note, does anyone know how many amps the electric breakaway brakes draw if they are activated?

It would kinda' stink to blow your battery fuse right when that feature is needed...

ChanW

I'll be interested to know too, for a different reason (we have surge brakes). Before we picked up our Tab at the dealers, I'd installed a 7-pin 'kit' from eTrailer, that included a duplex 10ga wire that was intended for the 12v 'battery charge' line and the electric brake line. 

Does the electric brake system draw that much? I'd prefer to use the other 10ga line for the return to the negative terminal in the TV.

Photomom

This kind of ambiguity bugs me. There should be a right answer, and LG should know what it is. 

ScottG

So many good questions, I'm having a tough time peeling myself away this morning. I just made my fifth trip out to "check something" on the T@B or TV.

Under the hood of my truck (which has the factory tow package) are two additional fuse boxes. One of them has a slot labelled "electric brake" and that slot contains a 30A fusible link.

Not claiming to know what that means, just passing on information. Hoping somebody else can expand the body of knowledge here.

I do so enjoy ambiguity!  :-)

[Deleted User]

Yikkes, I hadn't thought about the electric brakes! I believe the circuit breaker box in the TAB has a 30 amp fuse labeled Battery Charger, but that circuit is only as strong as its weakest link, the 20amp fuse at the battery.  I hope someone can chime in on the amps of the electric brakes.

ScottG

Just to clarify, the electric brakes should be fine under normal conditions; they receive their power from the tow vehicle...provided the tow vehicle and trailer are still attached to each other.

My musing was more with regard to the emergency (a.k.a., "breakaway") brakes which activate in the unlikely event of a tow vehicle-trailer separation. In that case, the trailer battery powers the brakes to help stop the now freewheeling trailer. The battery is connected directly to the breakaway brake switch via a junction box under the front of the trailer. The circuit breaker box/converter is bypassed in this situation. However, the fuse at the battery is not--if it blows, the brakes will not stay activated in a breakaway situation.

So, my thinking (fuzzy as it may be) is that if my tow vehicle allows up to 30 amps for the brakes, my trailer battery probably should also.

Presumably, LG put a 30 amp fuse at the battery for a reason. Why they didn't also install a proper 30 amp fuse holder is another question...

[Deleted User]

Thanks Scott for this additional info. My concern and fear is the fuse blowing in a "free wheeling trailer" scenario! YIKKES!!!  I see the 10awg, 30amp fuse holder on Amazon. I'm going to go ahead and order that and switch out the 12awg wiring just to be safe. LG put a 20 amp in mine, AND, the Owners Manual (and I use this term loosely) specifically states not to replace the 20amp with anything higher.  My current holder says use only a 20amp fuse.  I think I might call the manufacturer to see if I can find out why they installed the "step down" wiring in the first place. Maybe they had a good reason.

ChanW

Let us know if you find out. It seems there are a number of opinions about the value of the battery fuse, and this isn't something that's 'a matter of opinion', it's a specific, physical, absolute.

What should this fuse's amperage rating be?

Mods, can you possibly get a definite answer from LG on this? (Thanks!)

[Deleted User]

Ok, I JUST got off the phone with the technician at little guy. His name is Donnie. He said by all means a 30amp fuse is perfectly safe in the 12 gauge fuse holder and in the event your trailer becomes unattached and the electric brakes need battery power, he said he "thinks" it would only draw 10amps. All the battery is needed for in this scenario is to engage the magnets. He said even though the owners manual says use only a 20amp fuse in there, he said that is old information and that since the 12 gauge wire (the thinner yellow wire) is so short that there is no concern of it overheating and melting.  The correct fuse is 30amp.  He said they have been wiring them with the red to yellow for many years now and there hasn't been any indication that this wiring configuration is not sufficient.  I still don't see why they didn't just use 10awg wiring and fuse holder all the way to the positive terminal though.  I see the correct fuse holder and wiring on Amazon for about $3 so I might just go ahead and rewire it but Donnie assures me this is not necessary.

ChanW

Ok, thanks for the update robyn769.

The 'no problem because of the short length of the #12 wire' makes sense.

Ratkity

Thanks for the explanation @robyn769!