Breaker size recommended given inverter wattage

**Mikec557** · 06-20-2020, 04:18 PM

I'm going to install an inverter into a newly acquired rv. I think on my last rv I may have gone overkill and upsized the inverter to a size far greater than I needed or would have a use for. The realistic goal of use is this: cpap, electric mattress pad, TV and blu-ray player. I guess in theory all three/four may be on at once, but that is extremely unlikely. I want to use an inverter with automatic power transfer because three outlets in the couch are already wired to a loop of romex in the pass through. The three outlets are all on one breaker in the main breaker/fuse box. If I put an inverter with APT at that loop of romex, the three outlets will always be powered whether on shore power or when the inverter is on.

All that said, I would ask what size fuse/breaker should I use given a 600 watt inverter APT, a 1000 watt inverter APT, or a 1500 watt inverter APT?

I can just about guarantee I won't be putting in a 1500 watt inverter but I thought I should add it to the question because one of the three outlets is in the kitchen. The inverter will be located approximately 4-5 feet from the batteries, two Battleborn 100ah lithiums.

Suggestions on the wire gauge size for each would also be appreciated.

Thanks
Mike

**JohnJCES** · 06-20-2020, 10:15 PM

I am not sure what 'APT' means but if you are running sensitive electronics, I.E?. cpap, I would use a pure sine wave inverter. I haven't seen any 600 watt units with automatic transfer relays. I have seen them on 1000 watt and above inverters. I'll answer to the middle of the road.
A 1000 watt inverter under full load at 12 volts in, using Ohm's Law, will draw at least 83 amps. Generally as the battery depleats, battery voltage goes down and current draw will go up. IMHO you will want at least a 100 amp circuit breaker.
https://www.cerrowire.com/products/r...pacity-charts/
The link shows wire ampacity. I'd use 2AWG welding cable. A bit of overkill in the 12 volt wire to the inverter will keep heat down in your wire and it is just safer.

**DarthMuffin** · 06-21-2020, 02:36 PM

Most inverters show a momentary or surge rating (like a 1000W may be able to do 1500W momentarily). So size for the smaller of that (using watts/12v rounded up to nearest convenient size breaker) or the max capacity of the wire you're using (there are wire charts online).

A 600W inverter that allowed for a 900W surge, I would wire with a 75A breaker and use 4GA wire for a <10ft run. Although if you use 2GA wire you can future-proof yourself in case you decide you really do need that 1500W inverter after all.

**Mikec557** · 06-21-2020, 03:03 PM

Originally Posted by DarthMuffin

Most inverters show a momentary or surge rating (like a 1000W may be able to do 1500W momentarily). So size for the smaller of that (using watts/12v rounded up to nearest convenient size breaker) or the max capacity of the wire you're using (there are wire charts online).

A 600W inverter that allowed for a 900W surge, I would wire with a 75A breaker and use 4GA wire for a <10ft run. Although if you use 2GA wire you can future-proof yourself in case you decide you really do need that 1500W inverter after all.

Thanks DM and JJC, and others if I missed anyone. I think I'm going to use the Xantrex Freedom X 1000 (isn't that an unnecessary mouthful). It calls for 2ga wire. It also specified a breaker I can't recall at the moment. I also swung by an RV dealership that had two units with the Xantrex installed. I was able to see the 2ga wire they used and the beginning and ending path of the wire. Of course it's a mystery how they fished the wire past the front pass through wall to exit outside underneath. The coroplast at the front was installed from above on the inside of the frame, then at the end of the tongue it switches to being fastened on from the outside underneath. So the first 3-4ft which I would love to peel down, I can't. I guess I'll start by widening the small hole in said front wall, where the Romex loop comes out. Maybe I'll see a path with mirrors and a flashlight.

**eodenc** · 07-03-2020, 08:55 PM

Originally Posted by Mikec557

Thanks DM and JJC, and others if I missed anyone. I think I'm going to use the Xantrex Freedom X 1000 (isn't that an unnecessary mouthful). It calls for 2ga wire. It also specified a breaker I can't recall at the moment. I also swung by an RV dealership that had two units with the Xantrex installed. I was able to see the 2ga wire they used and the beginning and ending path of the wire. Of course it's a mystery how they fished the wire past the front pass through wall to exit outside underneath. The coroplast at the front was installed from above on the inside of the frame, then at the end of the tongue it switches to being fastened on from the outside underneath. So the first 3-4ft which I would love to peel down, I can't. I guess I'll start by widening the small hole in said front wall, where the Romex loop comes out. Maybe I'll see a path with mirrors and a flashlight.

I'm curious what you have found for your wiring and how you are doing it. I just got two lion batteries and weighing my options for cost and ease of modification issues.

**Mikec557** · 07-03-2020, 10:04 PM

Originally Posted by eodenc

I'm curious what you have found for your wiring and how you are doing it. I just got two lion batteries and weighing my options for cost and ease of modification issues.

I can give you a fuller answer and more pictures tomorrow. But in a nutshell I decided not to cut open my coraplast, nor drill blindly through it. I came from the batteries on the tongue, through the flat floor of the pass through on the driver side. I used a gray plastic electrical box to add some road-spray shielding. It will make more sense when I can show you a picture.

**Mikec557** · 07-04-2020, 03:10 PM

Originally Posted by eodenc

I'm curious what you have found for your wiring and how you are doing it.hi I just got two lion batteries and weighing my options for cost and ease of modification issues.

EOD

I looked up the travel trailer in your signature but I couldn't tell if GD did any "prewire" for an inverter or a solar charge controller. Prewire makes it sound like a big task on the Manufacturer's part, but it's not much really, at least for the inverter. The solar charge controller isn't any fancy wiring either but it does involve the added expense of putting a entry port on the rooftop. But seriously, the retail price of that part is less than $100. It just takes a little effort during the build which would eliminate a great, and precarious effort, by the buyer later on.

In my case, my manufacturer is Keystone. And mine was an early run on a new idea. So they only got it half right. Solar connector is on the rooftop, runs down the inside of the front pass through wall, out the underbelly, and connected to the battery. No loop of excess wire in the pass through. So I couldn't just cut the 8ga wire and put my solar charge controller in the middle between the rooftop port and the batteries. I disconnected from the batteries, pulled up about 2ft of wire and cut off the rest of the wire running out towards the battery. That gave me 8ga from the rooftop port, down the inside of the wall and into the pass through where I mounted my charge controller. Getting from the charge controller to the batteries was all done on the board in my above pictures. I sent the output of the solar charge controller to the positive and negative bus bars you can see in the above pictures.

I fed the bus bars with 2ga wire from the batteries. I connected the inverter/bypass to the same bus bars with 2ga wire.

I got lucky on the inverter "prewire." They ran Romex from a breaker in the panel to the pass through, gave me close to 4ft of Romex loop, then it went back into the wall and on to an outlet in the bedroom, then 1 in the kitchen, and finally to 1 by the TV. I cut that loop and fed the hot side into the inverter/bypass and the other end to the output of the inverter/bypass. If the i/b is on, it defaults to feeding the Romex output from the shore power. If there's no shore power it will pull what it needs from the batteries, invert that to 120vac, and then sends it out to the bedroom, kitchen, TV (assuming it's on and that you've turned something on that's plugged into one of the three outlets. If the i/b is off, shore power will still pass through, but if shore power is off it won't invert and power the three outlets, until I turn it on.

Here's a few more pics

Nearly on topic: there was barely enough room for 2 group 27 batteries on the tongue. I had to relocate the two red self-resetting circuit breakers to gain a little more room. And I had to trim off the handles on one end of both battery boxes to they could scoot closer together. Then I had to trim off half the overhang on one end of both tops. And I had to 69 the tops to get them to fit on the boxes.

Let me know if you have any questions.
Mike