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Old 12-16-2009, 07:24 AM   #1
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Inverter question ??

My MH didn't come with an inverter- .

I installed a pure sine wave 1000 watt Cotek inverter. I also installed an automatic transfer switch as folks here on iRV2 have told me I had to do. I used 12 ga wire.

Here's the problem-
If the inverter is on and I hook up shore power, it trips the ground fault breaker on the inverter. I called the engineer "VJ" in Canada that designed this unit. He told me it has to do with the "neutrals" in the motor home. The power from the inverter to the transfer switch has to be taken from the inverter BEFORE the GFCI. Now, how in the world do I do that? Incidently, he is talking so far advanced to a layman (me) with his technical terms, I get lost in a hurry.

"VJ" says they can't, because of "code's", produce a unit without a GFCI receptacle for me to plug my output cable into. I guess I should have bought an inverter with a built in transfer switch. The output cable is taken directly from the inverter, not a "plug in" like I have.

Would that have worked out better for me?

Having said all this, I can still use my inverter as long as I turn the inverter off before I plug into shore power. I also installed a remote "on/off" switch in the bedroom so I don't have to go into the battery bay to do that. I just have to remember to turn it on before I take off.
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Old 12-16-2009, 08:55 AM   #2
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Max,

I went to the Cotek web page here
, according to them, their ST series inverters have a built in transfer switch. What model do you have?

Also, I see your rig is a 2003 Dutch Star, are you sure it doesn't have a factory installed transfer switch?? You may have added a transfer switch unnecessarily.
If you rig has a generator, which I'm sure it does, there has to be a factory installed transfer switch.

I installed a 2KW Magnum Pure sine wave and here is how it's wired, I'll keep it simple.

The output of the transfer switch feeds my main AC breaker panel, the AC output from that panel becomes the AC input to my inverter, the AC output of the inverter becomes the input to an AC smaller breaker panel that feeds things like my Fridge, TV, Sat receivers etc. When the inverter detects AC incoming, the internal transfer switch passes AC through to the sub panel. When I dry camp, my batteries feed the inverter and the sub panel.

[QUOTE]The power from the inverter to the transfer switch has to be taken from the inverter BEFORE the GFCI. Now, how in the world do I do that? Incidently, he is talking so far advanced to a layman (me) with his technical terms, I get lost in a hurry./QUOTE]

You do this by connecting to the output of your transfer switch.

Hope this helps and doesn't add a confusion factor.
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Old 12-16-2009, 09:20 AM   #3
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First.. I'd like to know why the )(*#$@# they would bother with a GFCI on and inverter.. Ok, so they did

Simply replace it with a standard outlet.. Or, open the inverter's case and you will see where to tap power off before it

GFCI outlets usually have both a LINE and a LOAD screw as well as neutral and ground...

To tap off.. Remove the plug from the 12ga line to the transfer switch

Get a short (3 inch or so) piece of 12ga wire (NOTE: this may not be needed depending on if the outlet has wires or screws, some GFCI outlets have wires)

Remove the Hot (Black, usually) wire from teh back of the GFCI, using a wire nut splice the short wire, and the line to the transfer switch to this wire (Black to black) Re-attach the short jumper to the GFCI.. If the GFCI already has wire leads. you don't need the jumper

Do the same for the white, and the Green/bare

DO one wire at a time WITH THE INVERTER OFF

And other than routing and securing the wires.. that's about it.
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Old 12-16-2009, 09:47 AM   #4
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Tincup,

Thanks. I have the SK1000, no built in transfer switch (of course). I have an 37', '02 Mountain Aire. I like the idea of tying into the coaches ATS since the 12 ga cable I ran from the inverter goes right next to the ATS. Would I have the same problem, since I'm still taking the inverter output from a GFCI?

wa8yxm,

Thanks also. I'm printing out these answers so that I can plan out a course of action.

The inverter works great except for this glitch.
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Old 12-16-2009, 05:53 PM   #5
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Max,
I do have an inverter in my 3778. Let me know if I can trace any wiring or take pictures for you. It looks like it may have been unstalled by Newmar dealer and not the factory. Either way it works just fine. I also added a remote on off switch although on the dash.
Let know if you need details of my configuration.

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Old 12-16-2009, 07:27 PM   #6
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Max- I believe you have a Cotek SK1000, no auto-xfer switch. Code calls this a "separately derived" power system, as it is separate from the normal power company input.

A GFCI trips when it senses that not all the output amps are perfectly matched by the input amps, even by a tiny amount.

Your inverter has a neutral wire for the return of the 120V that goes out on the hot leg, and a hot wire. In your coach, I assume you connected this neutral to the coach neutral and hot to the coach 120V panel. With 4 tires on the ground and not connected to anything electrically, your coach & inverter neutrals go nowhere. They may be (in fact I'm sure are) bonded to the chassis frame, but there's those tires keeping them ungrounded. They connect thru a "load" like a power tool. If the GFCI reads a small difference in the hot leg output vs. the neutral leg input, the tool has a minor short that might be drained off thru you, so it trips.

The RV electrical pedestal has a neutral, and it is connected to a ground rod, usually visible right next to the pedestal base, which can establish a different potential than the closed circuit setup on the coach (not by much usually, but this is GFCI-trip territory). So here is genuine earth ground, and neutral = earth ground at this point vs. your isolated coach frame. When you plug in, I'm guessing either 1) the difference between your isolated coach neutral and the pedestal neutral is more than the difference allowed by the GFCI, or more probably 2) the voltage (and therefore amperage operative within any circuit using the inverter) is different on the pedestal vs. the Cotek and zappo- your GFCI trips. Basically you are connecting two sources of power & neutral/ground that would only be matched if serendipity smiled.

If you had an auto-transfer switch, then only one source (power co. or separately derived 120V coach power from inverter) would be operative at one time, and it stands a much better chance of balancing internally.
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Old 12-18-2009, 01:11 PM   #7
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E Mike-

I have a seperate Automatic Transfer Switch that I installed just for the inverter. "VJ" the design engineer told me basically what you told me, about a slight misbalance in amps/loads would trigger the ground fault with all neutrals being tied together. As I ponder my dilemma, I think the best, and easiest, course of action to take is to change out the GFCI output receptacle with a normal receptacle.

As wa8yxm mentioned above, why it was designed that way is bad for my application. "VJ" told me to tap off the inverter power before the GFCI. This is a big job so I'll defer it until I'm not living in the rig. It requires me to disconnect all AC power, disconnect the battery power and remove the inverter from the small bay and large copper cables (2/0) I used for the install.

Thanks for your input all,
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Old 12-18-2009, 08:11 PM   #8
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Now this is purely a Hypothetical question??

If a fellow wanted to defeat the inverters GFCI built in breaker, in it's receptacle, by going to a two wire plug, is that possible?? There is no RV outlet receptacles I'm using near a water source.

We have a vacuum cleaner that only has a two wire plug. Some of my power tools at home only have two wire plugs.

Again, this is a hypothetical question looking for only a hypothetical answer.
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Old 12-20-2009, 11:08 AM   #9
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I've answered my own hypothetical question .

The grounding circuit has no effect on the GFCI breaker tripping. It still trips.

I will look at replacing the GFCI receptacle with a non- GFCI receptacle.

It doesn't appear to be as big a job as I thought originally.
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Old 12-22-2009, 08:51 PM   #10
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You are confusing three-wire vs two wire with GFCI - they are not related. A non-GFCI outlet still has a ground (theird prong) and has three wires. As you have already noted, the ground wire has nothing to do with the GFCI. A GFCI outlet or breaker measures the amperage flowing in the hot and the neutral and opens if the two are not identical.
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