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Topic ClosedMorningstar inverter wiring

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bonanddoug View Drop Down
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Direct Link To This Post Topic: Morningstar inverter wiring
    Posted: 18 Aug 2014 at 9:48pm
I have a question about grounds on the Morningstar Suresine. The diagram shows a plus, minus and ground for DC and also shows the neutral tied to ground at the AC output of the inverter.  Since the only 'ground' is the chassis of the RV and this is also the DC negative I am somewhat confused as to how the wiring is done.  I know that in household wiring tying neutral to ground is a bad thing.  How did people who have installed one of these inverters done the wiring?  Thanks.
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Direct Link To This Post Posted: 19 Aug 2014 at 8:14am
I looked at Morningstar's Documentation. I think that you can tie both the Earth Ground and the - terminal into the Chassis ground on the trailer. Morningstar recommends that the earth ground be a larger wire than the - terminal. You should use separate wires for the Eath Ground - terminal and the AC neutral. 

In your household wireing the neutral is tied into the ground. You just have to make sure that it is tied into the ground in only one place at the electracal box. You can't have more than one ground point. 

Edit: found this diagram that shows the AC Neutral and earth ground tied together. they show direct from the negative post on the Battery but I don't see an issue with using a Chassis ground for the negative. 

Are you wireing this into the electrical system of the Pod? 


Sean, 2011 Rpod RP-173,2009 Jeep Liberty Rocky Mountain Edition
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bonanddoug View Drop Down
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Direct Link To This Post Posted: 19 Aug 2014 at 10:25am
Yes I am going to put it in my Rpod.  I guess I see it's ok to connect ground and neutral at a single point in the system and this is a separate system.  The separate ground on the input is a little harder  to figure since I am connecting the minus to a wire that is attached to the chassis at some point already and then they want a separate wire from the inverter input ground to the chassis.It seems equivalent to tie ground to negative at the inverter.  There is a slightly different wiring diagram on the morningstar website http://www.morningstarcorp.com/wp-content/uploads/2014/02/ALL.DIG_.Correct_Inverter_Wiring.01.EN_.pdf .  Thanks for the information.
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Direct Link To This Post Posted: 19 Aug 2014 at 12:55pm
NO!  Make sure you do not bond the AC neutral to ground anywhere in the pod, only the DC negative.  The single bonding point is supplied by the campground connection, by code.  Many smaller generators do not provide the N-G bond so you get a "floating ground" when you are hooked to them, and this inverter is like those generators.  You can create a N-G bond at the generator (which makes it marginally safer) but that is because that N-G bond will disappear when you unplug from the generator and then plug into the power pole at the campground. 
 
Things are a bit trickier with this inverter because if you wire it as they show, the extra N-G bond will still exist when you go to plug into the power pole.  Now you'll have two bonds, which is against code, and can cause odd problems due to ground loops - up to and including a fire.  Your two choices are to either leave it as a floating ground, or add an expensive transfer switch which will also switch the neutral.  Those are usually only found in large motorhomes.  Ones found in home backup systems usually only switch the legs, because the N-G bond found in the utility panel is the single bonding point whether on utility power or generator power.
 
Floating grounds on portable generators and inverters aren't bad.  Adding a N-G bond to them is only marginally safer, and isn't any safer in this case if you are only feeding a single outlet.  The reason the N-G bond must exist when you are plugged into utility power is the earth under your feet is actually part of the electrical system.  An electrical fault can travel through your body, through the earth, and electrocute you.  That isn't possible with smaller generators and inverters when the AC output is left floating.
 
Leave the neutral floating, and feed a GFCI outlet to add a layer of protection, and you'll be fine.
 
A side note, the ability to bond N-G is only possible with true sine wave inverters like the Morningstar.  Cheaper modified sine (or square) wave inverters will actually fry if you try to create a N-G bond.  Your only option is to use them with a floating ground.
Doug ~ '10 171 (2009-2015) ~ 2008 Salem ~ Pod instruction manual
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Direct Link To This Post Posted: 20 Aug 2014 at 8:29am
Originally posted by techntrek

NO!  Make sure you do not bond the AC neutral to ground anywhere in the pod, only the DC negative.  The single bonding point is supplied by the campground connection, by code.  Many smaller generators do not provide the N-G bond so you get a "floating ground" when you are hooked to them, and this inverter is like those generators.  You can create a N-G bond at the generator (which makes it marginally safer) but that is because that N-G bond will disappear when you unplug from the generator and then plug into the power pole at the campground. 
 
Things are a bit trickier with this inverter because if you wire it as they show, the extra N-G bond will still exist when you go to plug into the power pole.  Now you'll have two bonds, which is against code, and can cause odd problems due to ground loops - up to and including a fire.  Your two choices are to either leave it as a floating ground, or add an expensive transfer switch which will also switch the neutral.  Those are usually only found in large motorhomes.  Ones found in home backup systems usually only switch the legs, because the N-G bond found in the utility panel is the single bonding point whether on utility power or generator power.
 
Floating grounds on portable generators and inverters aren't bad.  Adding a N-G bond to them is only marginally safer, and isn't any safer in this case if you are only feeding a single outlet.  The reason the N-G bond must exist when you are plugged into utility power is the earth under your feet is actually part of the electrical system.  An electrical fault can travel through your body, through the earth, and electrocute you.  That isn't possible with smaller generators and inverters when the AC output is left floating.
 
Leave the neutral floating, and feed a GFCI outlet to add a layer of protection, and you'll be fine.
 
A side note, the ability to bond N-G is only possible with true sine wave inverters like the Morningstar.  Cheaper modified sine (or square) wave inverters will actually fry if you try to create a N-G bond.  Your only option is to use them with a floating ground.

Thanks Doug,

I think that is what I was trying to say when I asked him if he was hooking it to the electrical system in the Pod. Yours is way clearer. 

Moringstar's website does not cover this very well but when I was going through their customer forum and the vehicle installs all have the earth ground left floating and no N-G bond.


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bonanddoug View Drop Down
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Direct Link To This Post Posted: 20 Aug 2014 at 10:00am
I guess I misunderstood the part about hooking into the electrical system.  I am connecting the DC to the rpods DC system and running a separate outlet for the inverter.
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Direct Link To This Post Posted: 20 Aug 2014 at 10:18am
I can't find a Morningstar customer forum.  Could you post a link?  You are saying I dont need the ground connection to the input side of the converter, just the plus and minus (with a circuit breaker).

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Direct Link To This Post Posted: 20 Aug 2014 at 10:55am
So what exactly is the purpose of adding this inverter?  Doesn't the trailer already have what is needed?
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Direct Link To This Post Posted: 20 Aug 2014 at 11:28am
So you can run *some* 120v stuff when hook ups aren't available. It "makes" 120v from 12v. 
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Direct Link To This Post Posted: 20 Aug 2014 at 6:12pm
Originally posted by bonanddoug

You are saying I dont need the ground connection to the input side of the converter, just the plus and minus (with a circuit breaker).

In the diagram above, don't install the connection between the neutral and DC negative (the top-most wire on the diagram).
Doug ~ '10 171 (2009-2015) ~ 2008 Salem ~ Pod instruction manual
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