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  1. #1
    Bobtail Member
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    circuit breaker for power inverter

    Hey guys I have a 1500w inverter and a 700 watt microwave. I also have an inline 100 amp fuse but.it keeps blowing. Just curious what size circuit breaker I should install instead of the fuse. And no.I'm not going without some sort of protection for the wiring


  2. #2
    Road Train Member mickeyrat's Avatar
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    watts X volts = amps.

    read the rating on the back of the microwave to find your amps.

    or it may show volts and amps. Use the same formula to find true wattage.


    is there anything else being used when the micro blows the fuse?
    Last edited by mickeyrat; 06.18.2012 at 09.51 AM. Reason:: added question

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    Bobtail Member
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    No I run it solo

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    Quote Originally Posted by mickeyrat68 View Post
    watts X volts = amps.
    Not exactly.... volts x amps = watts. watts/volts = amps. OP's situation of 700w/120v=5.8 amps.. round up to at least 6 to include the light and carousel. Making the assumption that the MW runs off the inverter (in case I'm confused again). Converting to DC, your MW should be (in theory) drawing 58+ amps from the 12V battery, not counting any power loss through the inverter.

    Couple of things may be happening-OP didn't state if the fuse blew immediately or after MW had been running for a little bit. That said, the startup surge may be enough to spike the current draw to blow the fuse. The voltage may be a little low coming from the inverter, MW startup might drop output voltage down, which may cause excessive power draw on the 12V line. Microwave may be defective and pulling more than 700W of power at 120volts. How about the refrigerator? is that connected directly to 12V circuit (separate from the inverter) or running through the inverter?

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    Micro is new. Blows.after about 30 seconds. The refrigerator runs off inverter but I unplug it before using micro.

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    Quote Originally Posted by jdutton1 View Post
    And no.I'm not going without some sort of protection for the wiring
    I have bad news, the protection needs to be sized per the ‘wire size‘. Too big of a circuit breaker is like no protection at all.

    You need to get the amp draw (most likely rated in Watts) of the oven. If the oven is higher draw than the stock fuse you need to get a new circuit or oven.

    I’m sure there are some who say “I run an oversize fuse all the time and it doesn’t hurt a thing”. Those are the same people you’ll hear saying “Dumb trucks not worth a crap, they keep catching on fire”

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    Bobtail Member
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    I ran #4 wire?

  8. #8
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    I didn’t realize it was a circuit you ran, this is good since you know more about the circuit. How long is the wire run?

    4ga is about maxed out at 100amps unless the is less than 15 feet long.

    Of course in the perfect world the 1500W pure sine wave inverter would never draw more than 125A and less depending on the load. If the wire is only about 4-6 feet long then you could test with a 125a fuse and keep checking the wire and connector temps, from there it would be your comfort level call.

    At this point I would say you need bigger 125A circuit wire (depending on length) or a smaller inverter. I’d think since your wired for a 1000W and your over is 700W use the 1000w size inverter.

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