Over current protection for inverter 120vac output

Pianotuna, what would that matter?
60 amps is more than 50 amps. The inverter is only capable of 120v AC so it can't be used to supply the 50 amp service fully. The neutral conductor of a 120/240v 50 amp service is only sized to carry up to 50 amps. Typically only the imbalance of the 2 legs. If you tried to power both legs from the same in-phase 120v supply you could still only use 50 amps because any more and you would overload the neutral.

Hi KD,

I do see a problem with the 60 amp transfer switch IF it is going to power both legs of a 50 amp RV--which as I'm certain you know is really 50 amps per leg--totaling 100 amps.

Since I'm only 30 amps it doesn't affect me.

I do not have a Magnum, but there are 3 overcurrent protectors (Well 4 technically) on my Prosine.

For current incoming: there is a 30 amp breaker in my main box.. If your Magnum is capable of 30 amps, and your RV is 30 amps. trust me it's protected. If you have a 50 amp rv you likely have a breaker, same as I do, in the main breaker panel.

Since my Prosine does not have internal breakers there is a sub panel, Three 15 amp breakers.. That said.. The prosine is only capable of about 20 amps (that is rounded) with 3 15's I can easily exceed that (it can pass 30). so if it is in inverter mode and I'm sucking say 23 amps... It will simply shut down as it's electronic limiters kick in. I do not know if the Magnum has that ability.

I must say Magnum has me stumped. I'm an electrical contractor specializing in solar and off grid power systems. However, I've never worked with that particular Magnum inverter. I've never heard the term "branch-rated", it's not in the code book so I don't know where they got that from. I assume they mean that you shouldn't run your branch circuits from the 60 amp built in breaker and need to use other smaller breakers that are appropriately rated for your branch circuits. That would mean installing a normal breaker panel on the inverter output and putting your single pole 15 and 20 amp breakers in it.
As for putting a breaker in neutral conductor, that is pretty much never done.
In fact, the NEC doesn't allow it unless the breaker is designed to open both the hot and neutral poles simultaneously and there's no way they could be operated independently. A standard double pole breaker would meet this requirement. However, I can't imagine why they would want you to wire it up that way.
As several other posters have noted, the breaker supplying the inverter will limit the current it can pass thru. In the RV world this will be no more than 50 amps no matter what. Since the inverter is rated for 60 amps I don't see a problem there.
If you're curious enough I'd call Magnum's technical support department. From your call I would bet they will learn that whoever wrote their manual did a poor job.
I would just install your sub panel on the output and put the normal single pole breakers in.

Hi,

Make your life simpler. Feed the Magnum from shore power.

Feed the OEM shore power cord from the Magnum. Disable the OEM converter, but leave it in place as a back up.

Or if you must have that sub panel feed it from the Magnum. I disagree about what you plan to run from the sub panel. Unless there is a massive battery bank, and/or a massive solar system, running the air conditioner from the inverter is a poor choice.

The Magnum 3012 does not do voltage support, so protecting the electric motor on the air conditioner from brown outs at a campground will not work, unless the OEM converter is plugged into shore power and the rest of the RV is run from the inverter, using double conversion.

Remember that a 50 amp service offers the RV 12000 watts where as the inverter can only accommodate 3000 continuous (25 amps).

Unyalli wrote:
I plan on feeding the inverter from a 50 amp breaker on L2 in the RV's power distribution center.

-Jeff

Unyalli wrote:
How is the RV world supplying magnums requirement for an external neutral and hot circuit breaker? I've looked at a number of new motorhomes lately with magnum inverters and never saw a circuit breaker on the 120vac lines.

I must of have missed the requirement to break NEUTRAL ... hopefully my rig won't explode at some point.

As I understand the American (NEC) code, neutral and ground are a redundant safety system, and should never be interrupted, that's why (American) switches and breakers are always on the HOT leg of a branch circuit. I see in EUrope, they switch both conductors. I look at it like this, if a double pole switch fails, and for some reason opens the neutral but not the hot leg of a circuit, you have a dangerous situation. I guess in the EU, switches will never fail in that manner.

The external supply HOT circuit breaker should be in the subpanel where you plug in your shore power cord, the power pole / box / whatever... or you can be over protective and install your own master breaker inside the coach, feeding into the Magnum.

Go back to the ME website and there in their documentation you can find a complete wiring diagram for the coach. This should clear things up.

This will be a Magnum MSH3012M Hybrid inverter/charger with a 60 amp internal AC transfer switch. According to the owners manual pages 14 and 19 I am to use #4/0 and a 400 amp fuse on the DC side then #6 on the AC side with branch rated circuit breaker on the AC output. According to NEC tables 6/2 wire will handle 55 amps in my installation. The AC output will feed a sub-panel located 8' away. This sub-panel will have two 15 amp circuits powering the GFI and non-GFI receptacles and two 20 amp circuits one to the microwave and the other to the main air conditioner. I plan on feeding the inverter from a 50 amp breaker on L2 in the RV's power distribution center.

-Jeff

That caution is referring to "passthrough" current.
The inverter is supplied a/c shore power through the rig's main A/C breaker panel, input current is limited by a breaker in that panel.

Hi,

First of all, how many amps Can the inverter make? I would also guess that the battery fuse is a limiting factor too. So in my case I installed a Trace M1512 inverter in my motorhome with a 300 amp fuse and very large wire. The inverter can not continue to put out more than 30 amps without tripping the 300 amp fuse.

The circuit breaker feeding my RV is on a 20 amp branch, so that is the limiting factor while connected to shore power. If the inverter/charger is fed from a 20 amp shore power circuit breaker, no other protection is needed to protect the output wiring from exceeding 20 amps. However this can be limiting when you are trying to run the charger at full capacity as well as run some load fed by the charger circuit beaker, such as a microwave and also a heater at the same time.

Some RV's have a 30 amp circuit breaker in the shore power panel feeding the inverter/charger. Then the internal transfer switch feeds two circuits protected by inverter mounted 15 and 20 amp circuit breakers or sometimes 2 each 20 amp internal circuit breakers. This is the case with my friend's Country Coach and it's Trace inverter/charger.

Without looking at the pictured inverter/charger or it's installation in a RV, I can not determine how the wiring is protected. But it is safe to say that the inverter output will not exceed 50 amps for very long before the main circuit breaker feeding the RV trips. So the wiring is protected to some extent, but might not be protected properly from a prolonged overload that is just above the wiring's limits.

Lets take one look. If the RV has a 30 amp circuit breaker feeding the inverter and has two each #12 wires leaving the inverter output, then each goes to a separate area in the RV, the RV user might plug in 2 each 1,500 watt 12.5 amp heaters in the RV. This will not trip the 30 amp main breaker, but might overload one of the #12 wires. Probably not to the melting point, yet the wires might get warm or hot to the touch.

So if the inverter/charger does not have limiting circuit breakers or fuses on it's output, you might consider installing something. You can do this by limiting the input 12 volts with a fuse to only about 3,000 watts with a 300 amp fuse. You can protect the shore power size with a 20 amp or 30 amp breaker, depending on the load size wiring.

You can also buy "Edison" fuse holders. They are basically the size and shape of a standard light bulb holder, and will have two wires coming out of them. They fit into standard 1/2" knockouts. They hold a round Edison fuse, you can purchase those in 10, 15, 20, 25 and maximum 30 amp sizes, among others below 30 amps. Home Depot has a wide selection of Edison fuses.

Fred.