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Old 08-07-2017, 13:57   #1
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How to Wire an Inverter

I added a 4000 kw inverter and have been using it with direct plug-ins. I ran a 10 gauge 3 wire to the main panel, but don't know exactly how to tie in.

My 50 amp system has two lines with one for the airconditioning. I see where I can connect to the other line and neutral, so the 110v outlets will be powered. But, I don't know what to do with the utility ground - green wire. I think it will go back where the shore power green connects about 25 ft from the main panel.

I plan to add a 30 amp auto switch, so when there is no generator on or shore power, the inverter will cut in if it is switched on.

Do I have to do something about the battery charger?
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Old 09-07-2017, 04:25   #2
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Re: How to Wire an Inverter

First, I assume you mean 4 KW, not 4,000 KW (4 MW). That's 32 Amps at 125VAC, so you're just in the realm of a 30A circuit, and 10 Ga wire. So far so good.

You imply that the inverter does not have a built-in transfer capability. Here's where it gets tricky.

Your safety ground (green wire) should be bonded to neutral only at the "source." In other words, at the power pedestal when on shore power, but at the inverter when using that. Never both.

So as I understand it, your automatic transfer switch needs to switch all three lines; hot, neutral and ground.

A battery charger would have to be powered off a circuit which can not be fed from the inverter.

My own configuration is that only selected circuit breakers are fed through the inverter (which has in internal automatic transfer switch.) There are some things (electric range, electric water heater, battery charger, air conditioners) that I'll never want to power through the inverter.
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Old 09-07-2017, 04:49   #3
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Re: How to Wire an Inverter

What make & model inverter?
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Old 09-07-2017, 16:52   #4
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Re: How to Wire an Inverter

Thanks. I'll be home Tuesday and will give the model number. Right, I was too quick with 4,000.

Interesting about switching all 3 wires. I hope I can find such an animal. Does the inverter need to be separately grounded to water exposed metal?

I found the below diagram, but it confuses me. I do intend to leave the second black off the inverter - for air conditioner.

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Old 10-07-2017, 10:10   #5
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Re: How to Wire an Inverter

Wiring an inverter into an existing electrical system can be tricky. I'm surprised
that such a high capacity inverter does not have an integral transfer switch. Anywho, you could use a kraus & naimer three position rotary switch with 3 poles. Also, the inverter neutral output must be divided from the vessel's main neutral bus. That means you have to install another bus and move the neutrals for the outlets, microwave, TV, etc that you intend to power with the inverter to that new bus. If the builder didn't mark the neutral circuits, it can be very hard to tell what goes where. If you don't separate the neutrals, you'll likely have GFI breakers popping all the damn time.

Honestly, this is one installation that might be better left to a pro.

Good luck,

Scott
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Old 10-07-2017, 10:54   #6
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Re: How to Wire an Inverter

Thanks again! I think I am in over my head and will seek a pro. You did give me an idea though. I can trace out a few sockets and power them all the time by inverter.
Another Q, the diagram I included shows the case grounded. I didn't do that. Should it go to the isolator as shown? They show a yellow ground symbol. Does that go to the engine block which go to my big zincs on the bottom?
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Old 10-07-2017, 17:32   #7
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Re: How to Wire an Inverter

They sell "Triple Pole, Double Throw" switches all over the place. They use those to isolate your house from the grid, during power outages, so your little home generator doesn't kill any linemen working on the wires.
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Old 10-07-2017, 17:39   #8
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Re: How to Wire an Inverter

Quote:
Originally Posted by GeneM View Post
Another Q, the diagram I included shows the case grounded. I didn't do that.
Chassis (case) ground to ground bus at panel.
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Old 10-07-2017, 21:44   #9
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Re: How to Wire an Inverter

Inverters are tricky to wire safely. While you could do it with the three pole switch, you will have to always remember to switch when connecting shore power.

An inverter with an automatic transfer really makes things easier and safer in my opinion. My suggestion would be to sell yours and get a decent inverter charger with a transfer function. I have mine wired directly to shore power and then AC power goes to the panel. Simple and mostly automatic, only need to switch it off when using the SSB radio.

You also need a massive fuse on the DC side... Close to 400 amps. Think twice if you really need 4KW on a boat. Just the cost of the DC cables and the effort to run them through is significant. Not to mention the required battery capacity.
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