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Old 10-25-2017, 09:46 AM   #31
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This is a super interesting thread.
Learning heaps (as usual!) by reading through the collective SMB Forum knowledge/experience.

I'm curious --
At what point does an electrical system in an RV become complex enough (or electrically powerful enough) to warrant a fuse between the house battery and the 12V panel? (Or any other device that draws 12V?)

It sounds like any RV with an inverter warrants one automaticallly, as illustrated by the content of this thread. But what about simpler systems without inverters (and without generators?) "Lightweight" RV setups where the house battery only operates some 12V lights and perhaps a refrigerator?

Or (here, I'm showing more naivety) -- in the instance of a solar panel setup --- (which I still haven't installed) -- I'm assuming the solar panel "feed lines" to the solar controller are most likely fused, but how about elsewhere? (If you have a generator, you've probably got an inverter, so in that case I would expect a fuse is part of the equation automatically....)

At this point, I have the collective impression that a fuse between the house battery and the 12V panel is only "necessary" when there are high amp-draw items hooked up to it, like an inverter. In the case of an RV electrical system where the batteries only supply 12V to a series of low-amperage devices (each of which is individually fused at the panel), is it indeed ok to leave straight/un-interrupted (non-fused) supply lines between the house battery and the 12V panel?

(Full disclosure: SMB Fresno built my particular SMB in 1995 without a fuse between the house battery and the main 12V panel...and that's still the way she sits....so this is why I ask...)

Again, hope this question only enhances the collective group conversation here (and possibly helps others like myself who always benefit tremendously from reading these problem-solving threads!)

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Old 10-25-2017, 10:30 AM   #32
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So to be clear the fuse in question is for the inverter/charger not the battery.

RVIA apparently does not demand that the Battery be fused as opposed ABYC. I would expect ABYC to be more strict, if the boat catches on fire you have a bigger problem if your RV catches on fire.

That said, I recommend that the battery be protected per ABYC standards, and run that on my rig.

This is the class T fuse I added on my rig. It is close to the battery


The inverter/charger is a power supply and thus is required by RVIA to have fuse protection within 18" The fuse is in a bidirectional circuit, and thus needs to handle the requirements of the inverter and the output of the charger. The inverter requirements demand more current so they are the driving force in the choice of circuit protection.

Sportmobile will fuse or add circuit protection for fuse panel , any device that draws current before the fuse panel should also have proper circuit protection.

In general fuses are to protect the wire, so anytime a branch circuit changes wire size there should be fuse that adequately protect the transition to a smaller size wire.

Of course your wire size should be defined by the current and voltage drop requirements of the loads they are going to.

On your solar install, you should fuse the wire from panels befote they go through metal of your van at a minimal. The charge controller should be fused close to it and then you can fuse the other end (Branch) appropriately if it is long enough and the wire changes size . So if you were running 2/0 gauge to the inverter and you tapped off of the class t fuse to go to solar with 6 gauge it would be proper to correctly fuse the output or the charge controller and the transition from 2/0 to 6 gauge. If the wire is short enough the one fuse could be good enough for both sides if that makes sense. Also I expect that the fuse branch connection would not be required by RVIA, but would bring additional safety, especially if it goes through metal, etc.



hope this helps,


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Old 10-25-2017, 10:57 AM   #33
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Quote:
Originally Posted by MountainBikeRoamer View Post
This is a super interesting thread.
Learning heaps (as usual!) by reading through the collective SMB Forum knowledge/experience.

I'm curious --
At what point does an electrical system in an RV become complex enough (or electrically powerful enough) to warrant a fuse between the house battery and the 12V panel? (Or any other device that draws 12V?)
Pretty much you should have some sort of fuse that has a sensible limit between any battery coming into your 12 volt system. Having them close to the battery is good safety in case of a short to your main battery cables coming in. Looking at your batteries cold cranking amps and you will know right there how many amps you could possibly be putting into any short or compromised connection.

You should then have fusing or switched breakers for any distribution panel and the same for any load coming in or out of the system.

For instance, I have terminal fuses on my incoming battery cables from my starter and house batteries. 150 Amps each. Then I have A-Series switch breakers for my main 12v distribution panel, 120v charger, solar panels, and solar controller. These give me the next level of protection as well as a way to shut down that incoming or outgoing power. Next level of protection are simple blade fuses at the load level.

Now I did not set this all up perfectly as my terminal fuses probably are much faster acting than my breakers and blade fuses. Ideally you want them to blow working their way upstream. But the fuse and breaker sizes will most likely do that anyway.

Class T fuses are the stuff, but the terminal fuses I used are fairly close to them.

This is just my own sense about things and kind of fits with that electrical systems for buildings class I had 20 years ago. Basically you want to protect yourself from shorts by fusing close to the source. For the big loads at the batteries, use a fast acting fuse. Breakers are much more prone to failure and are way slower.

And yeah, everything Greg said. He's wicked smart with this stuff.
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