Placing your fuses or breakers in the wrong spot could leave parts of your electrical system vulnerable to dangerous overcurrents or short circuits. So where do you put fuses and breakers? Well, that’s exactly what we’re going to talk about here in lesson number three of this Breakers, Fuses, and Overcurrent Protection Playlist.
Fuse and Breaker Placement 101 – VIDEO
COMING SOON
So where do fuses go?
The most important thing to understand about fuse placement is the fuse should always go on the side of the wire that is closest to the battery.
Even if you have some kind of distribution system like the Victron Lynx Distributor, the Blue Sea SafetyHub, or the Tigerexpedition UFO 200 that has fuses inside of it, the fuses still have to be on the battery side of the wire. So you’ll notice here, battery here, wire here, fuse goes on the battery side. Load or charger here, wire here, the fuse is on the battery side of this wire. Same with these two here.
Now, if it’s a load, that makes a lot of sense because the flow of power is going this direction to power the load, whether that’s a refrigerator, a fan, a light, whatever the case is, we know that the power’s going this way, and that if we put too much load on this side, it’s going to blow that fuse or breaker there and stop the flow of power so that our wires don’t melt.
Where it gets kind of confusing is if this is a charger, because if this is a charger, the load is actually going this way. But if this is a 50 amp charger, it’s only going to be flowing 50 amps in this direction regardless of if it’s a short circuit situation or not.
A battery, it can discharge realistically as much power as we ask from it. Let’s say 1,000 amps, it can be more than that, it could be a little bit less than that, but that’s a lot of power.
If we have a short circuit right here, that fuse is going to blow because there’s going to be 1,000 amps trying to flow through that short circuit. Now, there’s still going to be power coming from this direction from the charger, but that power is only going to be 50 amps, and there is no way to protect on that side.
If we had a fuse on this side, this fuse is going to be large enough to sustain this kind of power under normal operational times, which is going to be 50 amps.
So this should have to be, let’s call it 60 amps to be able to allow this 50 amp charger to function normally. But under a short circuit situation, this fuse or breaker would never trip, it would never blow because this charger would be flowing only 50 amps. 50 amps could go either direction regardless of if it’s undercharging or if it’s under a short circuit situation.
So that’s why fuses are not on that side. We are only trying to protect from the 1,000 amp just massive overcurrent problem that we would have if we had a short circuit right here. And so that’s why fuses always have to be on the battery side of the wire regardless of what we’re powering.
So how does this concept look in a much larger system that’s got solar, that’s got charging from alternator, that’s got charging from shore power, has got multiple different loads, like 12 volt fuse blocks and 120 volt breaker bucks. Let’s just pull up a bigger, more comprehensive diagram and just go through it.
So here is the most popular electrical system that we have at shop.explorist.life. This one is for a camper van. It revolves around 400 plus amp hours of batteries, a MultiPlus 3K for shore power and 120 volt output, as well as solar and alternator charging and 12 volt DC output. So there’s a lot going on, and there’s a lot of fuses in this system to make sure that all of these wires stay nice and protected.
So we’re just going to go through this semi-systematically, and I’m going to show you where all the fuses are and sort of tell you why they’re there, but we already know why they’re there. They’re on the battery side of every single wire in order to protect the wire from a huge overcurrent event like a short circuit in the event that a positive and negative wire touch.
So let’s start at the bottom at the battery bank, and then we’ll move up. So starting at the very bottom, you’re immediately already going to notice that these wires from battery to battery, they don’t have any kind of fusing on them, and this is going to be largely up to a manufacturer’s recommendation. But since these wires are super short, usually only six inches or so, and they’re only going from one battery to the next battery and there’s really no chance of any kind of abrasion or a positive to negative connection, these aren’t required to be fused, but everything else is. This is sort of the one exception of this entire system.
This fuse right here, this is our ANL fuse. This could also be a class T fuse sort of depending on what size of system this is. But our systems as of today, they are ANL fuses here, and this is protecting the fuse that goes from the battery up to the Lynx Distributor. And you’ll notice that fuse is as close to the batteries as possible. It’s on the battery side of the wire.
Going up a little further. Once the wire and the power hits the DC distribution here in the Lynx Distributor, every single positive wire that is coming off of the Lynx Distributor is fused by a mega fuse inside of the Lynx Distributor. And so this means that this is the battery side, which means that this is the battery side, which means that on the wires here, this is a load, this is a charger, this is a charger, this is both a load and a charger, but it doesn’t really matter for our purposes because this is the battery side. That means the fuses are always going to be on the battery side of the wire opposite of the load or the charger.
Up here a little further, another sort of exception here is people a lot of times see the shore power inlet in the shore power cord, it’s getting its power from the shore power pedestal at like a campground or somebody’s house and going right into the MultiPlus. And you don’t see any fuses or breakers on this particular line. And that’s because there’s a breaker inside of the shore power pedestal.
Now, if you’re on a boat, the ABYC does recommend that you put a breaker within 10 feet of the shore power inlet, but that’s sort of one of those ABYC versus RV kind of specifications. In most of our cases, the breaker inside of the shore power pedestal is going to operate just fine to protect all of everything downstream of it. This is the same reason why you don’t have a breaker in between your wall outlet and your blender, for example, because that circuit is protected inside of the breaker box.
So going back down here, we got another spot for a, let’s see, this wire here coming into the DC to DC charger from the alternator. We’ve got our alternator, then a starting battery. Now, that’s a battery, that’s not the house battery, but it is a battery nonetheless. So the wire coming off of the starting battery here, going to the DC to DC charger down here, this is the charger side of this wire, this is the battery side of that wire, and therefore it needs to have a fuse or a breaker at the point of the starting battery.
A lot of times you’ll see somebody go ahead and put their breaker down here, and that leaves that wire totally unprotected in the event that these two wires right there were to short from an overcurrent event sort of started by that or powered by that battery. So that is why that breaker needs to be on that far end. It would be nice to be able to put it here with everything else, but it leaves the system unprotected. So we’re not really trying to do that.
This right here sort of looks like a breaker, and it technically is a breaker, but this is a discussion on solar because this is coming from solar. In this particular instance, this breaker, there’s not a battery. So that’s kind of an interesting concept, but this particular breaker is actually just being used as an on-off switch and not a breaker. It’s not adding any kind of fusing, breaker, or any kind of like overcurrent protection to that particular thing. So I just want to point that out that that’s what that was for, is more of a switch than it is an actual breaker.
Up here we have our standard just 12 volt fuse block, and this whole 12 volt fuse block, remember, is protected by this wire and this fuse that’s inside of the Lynx Distributor. Once this big wire comes up to the 12 volt fuse block to power all of our small loads like lights, fans, 12 volt refrigerators, stuff like that, this fuse block has a whole bunch of blade fuses just inside of that. So all of the really small wires, 10 gauge and smaller, those are all protected on the battery side of those wires by the blade fuse that’s installed inside of that fuse block.
Now, up here a little further, we have our AC distribution panel, and this is one of those things where the 120 volt AC loads that are coming off of it is protected inside of the breaker box right here, breaker box to the breaker, to all of the 120 volt AC loads.
Now, this is another spot where we can’t have the breaker at the point of the MultiPlus coming out. So this here, up here, this wire is protected on this end, and unfortunately, that’s just the way that it is. And we have to have these sort of considerations sometimes whenever there’s no feasible way to really do this otherwise. And so this wire, if there was a short circuit here, I mean, the MultiPlus is going to go into overload and it’s going to shut down. But there’s sort of no way to protect this from a short circuit event. But from an overcurrent event, if you’ve turned on too many 120 volt AC loads here and drew more than 50 amps of power for this 6 3 wire that’s here, then that 120 volt, 50 amp breaker in here is going to turn off, and it’s going to protect all of this wire going back this direction. But since that’s not a battery, that’s a little bit of a different consideration there.
So all of the systems on shop.explorist.life have this same methodology on them. We use the Lynx Distributor for DC distribution, for all of our systems, except for some of our smallest systems, which use the Blue Sea Safety Hub or the Tigerexpedition UFO 200, but they’re all the same concept. You’re feeding power from the battery to distribution and then distribution to everything. But the main takeaway is that every single positive wire is fused as close to the battery side as it possibly can be.
So I hope that clears up the confusion of sort of where to put breakers and fuses in an electrical system. And if you don’t really want to figure this out and make your own diagrams and stuff like that, all of our diagrams are for sale on shop.explorist.life, but more importantly, full kits. We have wires, fuses, breakers, all that stuff is sort of figured out as far as sizing goes. And then you can refer to the diagrams that we have and the tutorials that we have here on our YouTube channel for assembly. So I hope that clears things up, and we’ll see in the next video.
Overcurrents or short circuits, shirt circuit, shirt corcuits.
