Why do you need 6AWG wire on the AC input to a Magnum inverter?

SkykoSkyko ✭✭✭✭✭Solar Expert Posts: 121 ✭✭✭✭✭
I wired our camper shore power inlet to the location I plan to place a Magnum MSH4024M 4000 watt 24V input inverter with 8 gauge Ancor marine wire rated 600V insulation 105C. Our shore power plug and external cable are rated 30 amps.

I just reread the Magnum installation manual and they say use a minimum of 6AWG wire for all AC connections. They also say use a 60 amp breaker or fuse on the AC input to the inverter.

Is there a reason to use such a large wire and large breaker on the AC input if the plug and wire are only rated at 30 amps? 8AWG wire can easily handle 40 amps and the Magnum inverter is factory set to only draw 30 amps from the AC input. I am curious if there is any reason I cannot safely use the 8 gauge wire and a 40 amp breaker on the AC input wiring. If it is just an issue of slightly downgrading the surge rating or something I am ok with that as we will most likely never use more than 2500 watts or so. The biggest AC draw would be when the batteries are needing bulk charge 24V at 125 amps, but as I said, the Magnum is factory set to only draw 30 amps from the AC input.

Comments

  • solar_davesolar_dave ✭✭✭✭ Solar Expert Posts: 2,344 ✭✭✭✭
    Re: Why do you need 6AWG wire on the AC input to a Magnum inverter?

    More than likely it needs to match the device maximum to align with code.
  • Blackcherry04Blackcherry04 ✭✭✭ Solar Expert Posts: 2,490 ✭✭✭
    Re: Why do you need 6AWG wire on the AC input to a Magnum inverter?
    Skyko wrote: »
    The biggest AC draw would be when the batteries are needing bulk charge 24V at 125 amps, but as I said, the Magnum is factory set to only draw 30 amps from the AC input.
    Thats true, in your case # 8 with a 30 amp breaker would be fine. What you not taking into account is the the Pass Through + the Charger could put some installs over the limit. All your going to do is burn up your 30 amp shore plug if you use it for any prolong period of time. Shore Power cords will rarely handle their rated throughput, because the female receptacle never makes good contact and the Male plug burns out.

    If you have a removable Cord and a 30 amp hook-up on the trailer you better keep a good eye on it. They are a major source for a fire.

    A example of were the wire sizes between Shore power and Generator can be very different, I have a 50 Amp cord, but a 20 KW generator that capable of 166 Amp output @ 120V. 83 @ 240 V.
    .
  • SkykoSkyko ✭✭✭✭✭ Solar Expert Posts: 121 ✭✭✭✭✭
    Re: Why do you need 6AWG wire on the AC input to a Magnum inverter?

    Thanks. I had the idea to look at another inverter of similar size, the Outback. It actually states that you need 6AWG wire and 60 amp breakers for input and output AC for non-mobile applications but for mobile applications (our case) you should use minimum 10AWG wire and maximum 30 amp breakers on input and output.

    Of course the Outback doesn't do generator sharing so the 30 amp output breaker *could* be too small for a Magnum MSH4024M.

    It sounds like Magnum just lumps mobile and non-mobile applications together and covers it by saying use 60 amp breakers for both input and output AC.

    To me it is actually safer to use a 30 amp input breaker if you are going to be using 30 amp shore power. This way if someone for some reason changes the Magnum inverter settings to allow it to draw more than 30 amps you at least have some chance of not melting your shore power cable or plug (the 30 amp breaker might flip).
  • BB.BB. admin Super Moderators, Administrators Posts: 29,634 admin
    Re: Why do you need 6AWG wire on the AC input to a Magnum inverter?

    Many of the inverter/chargers do have a programmable maximum input breaker size...

    For code, a 30 amp rated plug/wire/breaker should only be run at 80% of rated current... Or 24 amps maximum in this case.

    If you want to run the magnum at rated input of 30 amps, then you need 30 amps * 1.25 NEC derating = 37.5 amp minimum branch circuit rating.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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