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Inverter Output Configuration

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This has been discussed below to some extent, but I think this more specific question deserves its own thread.


In the case of Generators or Utility Power I pretty well understand the design purpose and operation of GROUNDED systems which have a NEUTRAL, be it Floating or Bonded etc., and all the Transfer switch methods and configurations, which depends on how the Generator is configured.


HOWEVER not having access to Inverter diagrams and internal wiring schematics (and different types and brands may also ne different), I'm just unsure how they are configured. No problem with transfer from Utility to Inverter, you simply switch/transfer BOTH the Hot and Common or Neutral.


My "unknown" is if their output is in effect an "Isolation Transformer" (which I suspect) with 120 VAC Line to Line BUT NO NEUTRAL

OR if it even has a Neutral (which I doubt)

OR if it does and its a center tap on the output transformer (which I doubt) is it bonded to the case/frame, (which I also doubt)

OR if one leg (one end of the transformers output winding) is bonded to the case/frame (which I doubt)


OKAY CALL ME A DOUBTING THOMAS get the picture lol I suspect a straight 120 VAC Inverter output is an Isolation Transformer 120 VAC Line to Line HAVING NO NEUTRAL and no case/frame bond from any part of the transformer. I see no problem in bonding an Inverters case/frame to the RV frame which is also the DC Battery -.


Soooooooo does anyone have any hard evidence and schematic diagram of their particular Inverter to show how its output is configured????


If you take a continuity tester and attach one lead to the Inverters 3 prong receptacle, is there continuity from the Ground pole to Neutral??? is there continuity from Ground pole to case/frame????


NOTE if an Inverter were 120/240 (instead of a typical 120 only), then I suspect its the same as a utility transformer having a center tapped secondary


I have to go somewhere today but I plan to do that to my own 2000 W PSW Inverter when I can


Again even if one brand is configured one way, that don't mean another brand is grrrrrrrrrrrrrrrr I HATE NOT KNOWING its in my DNA lol In Law School when studying Trial methods the first thing they teach is when asking a witness a question NEVER ASK A QUESTION TO WHICH YOU DONT ALREADY KNOW THE ANSWER..........


Later gang, I'm headed out for the day, check back later.


An ever curious John T

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John - go back to the 'old' theory. The ground was the shell case (ie metal body drill motors) where if the line or neutral shorted to the case, it was a safe / return path for any power. Now, if it was the ungrounded (ie hot wire, L1 or L2) it tripped the breaker or blew the fuse. If it was the grounded conductor - neutral, it took any stray voltage current and doubled the return conductor size, dropping the voltage to a lower value.


Now, we also have double insulated tools and GFCI's to augment that protection


starting point - random inverter - Outback fx 25xx series - http://www.outbackpower.com/downloads/documents/fx_vfx_series/fxseries_installmanual.pdf


Read booklet page 21 (ACinput) (adobe pg 23)


Circuit diagram on page 30 (Adobe 32) 4 pole contactor that disconnects the shore power ground and connects it to the chassis. Also BONDS the Grounded conductor to the Chassis ground. I've seen the diagram for my xantrex 458 and the Victron and Magmun series also and they do the same thing.


A quick search turns up http://www.nfpa.org/assets/files/aboutthecodes/70/70-a2013-ropdraft.pdf draft of changes for the 2014 NEC code (NFPA 70) and if you do a Adobe search of that it turns up 56 inverter references. Pay particular attention to Art 551 (recreational vehicles) and about 551.31 +


I know, NEC code arugh -- I used to have the total NFPA on paper and (72 inches of shelf space) and CD and had to apply it all the time. With 11 plants in 6 different states and 17 million ft of manufacturing space you have to use it A LOT. Between that and the IEEE books, enough to drive a man to a beer.

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I read John's post a little differently. I read it as him pondering on smaller inverters, without the charge option. In this case, most manuals don't have any kind of technical info, and many suffer from a poor translation of Chinese to English. In 1 case, I have seen a schematic, but don't remember the brand. It did show a floating neutral, as John suspects. It had a 3 wire receptacle, with the bonding conductor tied to the inverter case, but neutral and line floating. I don't remember using a meter on it, so I can't confirm what the N to ground voltage was. I do remember that the instructions called for a bonding conductor of #10 AWG or large, to be connected between the vehicle frame and the inverter case.

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Point taken Darryl.


When John was talking about generators and inverters, I was thinking of the larger ones with the built in transfer switches.


My Prosine 1000 - http://www.xantrex.com/documents/Power-Inverters/PROsine/PS1000-1800Mounting_445-0133-98-01_Rev2.pdf - if you look on page 9, principles of operation, it shows the output and putting in a transfer relay. Isolated from ground, and DC return to the chassis.

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That Outback FX Manual was great I actually read much of it, the Xantrex link was only the first page. It looks like if you take the time to totally digest the NEC reference (I saved that, thanks) the answer lies within, and its the same difficulty I had interpreting the NEC way back when I was practicing, you cant read a line without having to go back to 2 or 3 references to understand it, and those also have 2 or 3 other back references and exceptions, it will drive you to drink. I thought briefing legal cases and researching statutes was hard in law school, that cant hold a handle to reading and interpreting the NEC lol I attended NEC Seminars by the likes of Joe McPartland and Mike Holt back in the day, now those guys were EXPERTS...............


YES I was thinking more about the smaller cheaper say 400 up to 1000 or 2000 watt Inverters when I posed the question




I think the more expensive Inverters may be wired and configured as what the NEC would consider a "Separately Derived Source" and may actually have a true Neutral which is bonded and I know and understand how to deal with and transfer such sources. HOWEVER I think the cheaper low end Inverters are similar to an isolation transformer output with 120 VAC Line to Line no Neutral and no bonding.




Sure I understand and might offer an opinion on supplying power to an Inverter, but not being 100% sure how its output is configured, I'm going to pass on any detailed wiring advice from now on. One thing regardless is to obviously use a 2 pole Transfer to switch utility Hot and Neutral to L1 & L2 of the Inverter regardless of all the other concerns, but Neutrals and Grounds I'm not gonna talk so much about unless its obvious and I understand it.


I feel better now, thanks for the responses. I think I better understand what it is I don't know now lol DO AS THE MANUFACTURER SAYS


John T Engineer and Attorney, one heck of a combination and curse causing excess concern over things like this grrrrrrrr

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LOL - yea John, it can get twisty??


Most of the bonding is done in the transfer switches. rather then hard wire. The saving grace on the 'intermediate' inverters is the GFCI. By measuring the in and out, and not through you, and the presumption that they are / will be used for portable including outside.


My 'fun' is using inverters to feed inverters with boost features. I do 90% of my power transfer - ie truck to trailer - at 120 volt and use synchronizing inverters. The old I^R loss issue.

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