Hard-Wired Inverter - Page 2 - Fiberglass RV


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Old 09-06-2008, 11:20 PM   #15
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I have completed the installation and testing of my 300 watt inverter and found the following:

If your inverter is going to be hard wired into your existing electrical system, the neutral has to be switched as part of the transfer.

[b]Why:

My trailer, like most modern trailers, has the neutral and ground isolated from each other. The ground and neutral connection is done at the shore panel. Connecting them together before the panel would create a ground loop.

So, when another AC source, like an inverter, is used the neutral and ground are still isolated in the camper and a ground fault will exist at the outlets. To prevent this, the neutral and ground should no longer be isolated from each other. The only way to connect them together temporarily, is to transfer the load neutral to the inverter neutral that shares a connection with ground.
It'll be a couple weeks before I can correlate with you on this, but hopefully I'll get back to this topic. I can say, however, that I'm currently hooked up to a 110v GFCI outlet, and with y inverter switched "Off" and my outlet circuit switched to "Shore" power, I'm not tripping any breakers (GFCI or overload breakers) or smoking any circuits.

I suspect, however, that if I went over and flipped my 12v power supply to my inverter to "On" I might well create a difference in voltage between inverter and shore neutral. That would, as you point out, be bad. I'll have to avoid doing that.
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Old 09-07-2008, 01:22 AM   #16
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Remember that the ground and neutral are only tied together at the first load center in the trailer, which is the 120VAC circuit breaker box -- Downstream from there, just as in your home, they are separated. The neutral and ground should NOT be connected at the shore panel.

OTOH, the shore power cable is analogous to the power company entrance into your home, and YOUR trailer load center SHOULD have the neutral and ground connected, just as your main load center at home. The only difference is that your home will (should) have physical ground rods.

What you seem to be doing is inserting a second load center (aka sub-main), but the neutral and ground should still remain separated all the way down to the load.

Likewise, the neutral and ground at the RV pedestal in the park should be separated, but these are often wired by the owner or a friend who may not know the code -- I have found all sorts of wiring problems in RV parks and never plug in without using the cheap test plug first. Another reason for being off the grid when I can help it.

We are chasing problems on a friend's house because the pro electrician combined the neutral and grounds in at least two sub-main boxes (well and dock) as if they were the primary load center. I'm afraid to open the sub-mains he has in his basement...

Also, keep in mind that, despite the title, GFCI devices do NOT detect ground faults, they detect imbalance between hot and neutral. You can lift the ground and nothing happens (although they will react to an imbalance even with the ground lifted).

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Old 09-07-2008, 09:43 AM   #17
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Remember that the ground and neutral are only tied together at the first load center in the trailer, which is the 120VAC circuit breaker box -- Downstream from there, just as in your home, they are separated. The neutral and ground should NOT be connected at the shore panel.

OTOH, the shore power cable is analogous to the power company entrance into your home, and YOUR trailer load center SHOULD have the neutral and ground connected, just as your main load center at home. The only difference is that your home will (should) have physical ground rods.
Thanks for the response,

I made an assumption that the neutral and ground were connected at the shore panel. A more correct statement would be: A real ground is provided after connecting to shore power.

[b]In hind sight, I should only state what I know for sure, and that is:

[b]1) My Bigfoot trailer, for sure, does not connect ground and neutral at any point in the trailer. I have metered and double verified this. Only when I'm connected to shore power do I have continuity between neutral and ground.

[b]2) In order for my inverter to work correctly, the neutral and ground must have a common connection?

I did not want to change the electrical engineering of my trailer by connecting them permanently. So, thought it best to transfer the neutral to make the connection. When the load is transferred to my inverter, the neutral / ground connection is made only in that branch. This way, it does not matter if both shore and inverter were active at the same time.

I have only worked on one other trailer and it was the same. So, I made the assumption that all modern trailers were this way.
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Old 09-08-2008, 10:15 PM   #18
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The camp ground's ground and neutral should only be connected way back where the power company connects to the main service entrance box -- After that, they are split all the way to the shore power box (where there should be at least one ground rod).

Likewise, your trailer should be wired just like you house or the CG, with the ground and neutrals connected on in the sevice entrance box and then separated.

Be advised that there are several ways manfs installed converter boxes; some with the 120VAC and 12VDC in the same box, some with 120VAC separate and some with both separate.
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Old 09-13-2008, 09:44 AM   #19
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Camping this week at one of Colorado's State parks gave me a chance to continue my testing.

Choosing a vacant site with electric hookups for my testing; I found the neutral and ground were connected together at the panel.
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Old 09-14-2008, 11:57 PM   #20
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If the panel was being fed from something like a meter then it is a SERVICE panel and that would be correct, but if it's just being fed by a breaker in another box (service or sub), then it's a SUB panel and doesn't meet my understanding of the code if the ground and neutral are bonded.

http://members.tripod.com/~masterslic/FAQ-2/18.html
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Old 09-17-2008, 11:04 AM   #21
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Pete, Thanks for the link. Dean
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Old 09-18-2008, 01:00 AM   #22
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My friend has a main panel in his basement and then a couple of sub-panels. I think one of the sub-panels feeds a sub-sub-panel at the head of his dock, where the ground/neutral is bonded and there are no ground rods (current code calls for two), and that in turn feeds a sub-sub-sub-panel on his dock, where the ground/neutral are bonded and of course there are no ground rods.

Likewise, his pump house is at least a sub-panel (maybe a sub-sub...), but it does have a ground rod.
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Old 03-08-2009, 06:30 PM   #23
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Thought I would do a quick update on my inverter installation (the first post in this thread covers the installation details). First, I've been very happy with our inverter setup. It's done a great job of keeping our laptop, cell phone, camera, and cordless drill batteries charged, which is about all we use it for.

I have, however, replaced the 12v power switch for our inverter with a rotary timer switch that I can set to run for up to two hours. That way I can plug in the device(s) that need to be charged up and leave for the day without drawing the battery down for no reason.


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The white decorator switch to the left of the rotary timer switches the power source for the outlets in the dinette to either shore or inverter power.
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Old 03-09-2009, 04:24 AM   #24
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Good idea putting timer on it!
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Old 03-09-2009, 04:53 PM   #25
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Don't forget to turn off your CONverter when using your INverter. (don't ask me how I know this... 8-)

Neutral and ground should NOT be connected together in an RV, with the possible exception of when running on a generator or inverter.

-- Dan Meyer
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Old 03-11-2009, 10:40 AM   #26
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Neutral and ground should NOT be connected together in an RV, with the possible exception of when running on a generator or inverter.

-- Dan Meyer
Yes, this is what my previous replies state. But when on an inverter, they must be connected to keep voltage off of the neutral, thus preventing a ground fault. This is why my transfer switch, switches both the hot and the neutral.

Dean
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