Magnum Inverter & a Sub Panel

[Thomas James]

I purchased a Magnum MS2812 Inverter for my 1994 Patriot. It had a Heart Interface 20D in it. One A/C input, and two outputs. The same as my new one. The folks at Magnum are telling me that I need a sub panel exit my Inverter. Something about back feeding to the main and doing some bad stuff. Well, the old one didn't have one. And I looked at the print, and the two A/C outs go to all the 120v outlets. And then of course my Microwave, Frig, and all that stuff plug into them. Can someone please explain to me WHY I need to install a sub panel?! Cause that's gonna be a real pain in the #$%. I actually had two friends of mine(who supposedly know more than I do)look at the prints, and they say the same thing....I don't need one. Help Please. And thanks in advance for any and all input. It IS appreciated.

[Edward Buker]

Tom,

Usually there is a sub panel on the output that defines the circuits that will be fed with the inverter and they contain breakers to protect the inverter. What that does is it keeps the inverter output AC downstream from the main panel and it is then in series with it.

If you backfeed the main panel you could then send inverter AC back toward the main AC powerlines, out of phase and that is catastrophic. You also would be sending inverter output AC back towards the input side of inverter through the main AC panel which is also a problem.

If you already had an inverter installed and it worked then you must have a subpanel of sorts which usually is mounted near the inverter or they just used the inverter as a pass through to a circuit that contained all the main AC components that you needed in the coach with no need for a extra subpanel with multiple breakers. That is quite limiting being just one 20 amp circuit but it is possible. My subpanel was just a small box housing four breakers and it was located on the ceiling of the storage bay.

You could have a coach that mounted the inverter nearer the main AC panel and then wired it in a manner that keeps the inverter output isolated from the input of the main panel. The concept is the same, the inverter output has to be isolated from ever seeing the input side of the main panel if there is any chance of generator or main powerline AC being coupled with inverter output AC.

I am confident that if you already had an inverter installed and you understand how it was wired and then wire the new unit in the same manner, then you should be OK. The key is understanding how it was wired before and seeing that the inverter is just a downstream component from the main breaker panel. Hope this helps.

Later Ed

[Thomas James]

Thank you very much ED. If I could send you the prints that I have for the coach, would that help?? Or should I just send them to the folks at Magnum?? Personally, I think it'll be fine. But I just don't know. Another thing I have to wire in is the AGS Module/remote. I guess I'll have to pull some wire for that. Not sure there either. Thank you for the help.

[Gerald Farris]

Tom,
I am not near as good as Ed with electrical issues, but I think that Magnum requires a subpanel after the inverter to protect the circuits after the inverter. With the only breaker in the inverter circuit being the 30 amp inverter input, the circuits after the inverter are unprotected from a short circuit when inverting. This creates a shock hazard as well as a fire hazard.

Most Xantrex inverters have a breaker on the inverter for each of the inverter outputs, but Magnum does not, so they require a subpanel to protect each circuit. However, if your inverter outputs run back to a breaker at the main panel area, you are good to go with the only unprotected wire being between the inverter and the breaker, but I doubt that your coach is wired that way.

Installing a subpanel is very easy. Just run a 10/2 with a ground or a 10/3 wire from the single Magnum output to a small two breaker box, with 20 amp breakers, that you mount next to the inverter and connect the two current inverter output wires to the breakers.

Gerald 

[Edward Buker]

Tom,

I did not know the specifics of the old inverter wiring but if it had two separate 20 amp breakers built in, then it literally had the subpanel built in. Thanks Gerald for clarifying what was causing the issue here in converting to the new inverter. As usual you can see the forest through the trees....

If the new inverter has replaced that inverter circuit format of two 20 amp breakers, with a singe 30 amp breaker then that has to be treated now as a main breaker. So basically 10/2 with ground is fed from the new inverter output main breaker to a small subpanel with two 20 amp breakers (typically a small grey box). Then the current coach wiring two 12/2 with ground circuits, that were on the output side of the old inverter 20 amp breakers, are now connected to those new breakers in the added box.

This is inexpensive and relatively simple components. Any lead manager of the electrical department in Lowes or Home Depot should be able to fix you up with what you need. Hope this helps.

Later Ed

[Thomas James]

OK, thank you Very much to both of you, Ed and Gerald. As I was talking to en electrician friend of mine here at work, that was kinda what I came up with(two breakers in a small box). I just wasn't sure what size. I WAS thinking 20 or 30(30 is the input fuse-white button). And both of you just verified what we were thinking. Thank You Very Much! It IS appreciated. So, all I need is a small box for two single pole 20A breakers for my two outputs. Cool. And I think I have some 12/2 left over from when I ran wiring in my shop. Now, to figure how to wire up the AGS Module. I know I need to pull wire from the Generator control panel. Oh well, one step at a time. Later guys, and Thanks again!

[Gerald Farris]

Tom,
Since the inverter output circuit is a 30 amp circuit, I would highly recommend that you use a short length of 10/2 with a ground or 10/3 to connect the inverter to the subpanel (small breaker box) that you are going to add instead of the 12/2 wire.

Gerald

[Thomas James]

Got it Gerald. That makes sense. Thanks.