Confused about inverter ground

Anything electric, AC or DC

Re: Confused about inverter ground

Postby capnTelescope » Wed Sep 30, 2015 12:24 pm

Dale M. wrote:capnTelescope wrote:
Even more folks won't know a thing about AC wiring and wonder why there is no red wire. ...

and
Dale M. wrote:Umm...240 AC Circuits have a red wire.... And if you are wiring a 3 way switch (120 V AC) the "traveler" is Red...

There ya go. Some of us know just enough to get ourselves in deep doo. I'd hate to mistake a 240 red wire for a traveler red wire. :frightened:

Dale M. wrote:http://ask-the-electrician.com/wiringdiagrams.html

Thanks for the link, Dale.

Dale M. wrote:I know its for a HOUSE but CONCEPT is same, TD is simply a little house...

Well said.

MtnDon wrote:I have a schematic with color codes for my trailer. Like the car mfg do. :) Helps to remember what is what.

Me too. Great minds think alike.

I just want to add that I've learned quite a bit in this after-discussion. Good work, Don, Dale and H.A.
I'll burn that bridge when I come to it.

Brad
ImageImageImage

Building the Bed & Breakfast
User avatar
capnTelescope
Lifetime member
 
Posts: 1218
Images: 368
Joined: Sun Jun 27, 2004 3:44 pm
Location: Round Rock, TX

Re: Confused about inverter ground

Postby lfhoward » Wed Sep 30, 2015 3:53 pm

This has been a fantastic discussion. Thanks to all who have contributed.

In my trailer's DC setup, I used red wire for outgoing (+) and black wire for returning (-). Then for the AC side, I used regular 14-2 Romex wire and electrical boxes like you would see in a house, using similar conventions. As of now, no AC ground (bare copper) is connected to the electrical boxes, because wood isolates the boxes from the rest of the steel trailer deck/frame. If you think I should do this, it can still be done.

Just a side note, my TD is wired for 15 amp AC, not 30 amp like an RV. It is basically just an extension of the electrical plug in my garage.
My off-road camper build on an M116A3 military chassis:
http://www.tnttt.com/viewtopic.php?f=50&t=62581
Tow vehicle: 2008 Jeep Liberty with a 4 inch lift.
User avatar
lfhoward
1000 Club
1000 Club
 
Posts: 1369
Joined: Wed Jan 22, 2014 6:10 pm
Location: Philadelphia, PA

Re: Confused about inverter ground

Postby H.A. » Wed Sep 30, 2015 5:08 pm

........
Last edited by H.A. on Mon Mar 28, 2016 5:15 pm, edited 1 time in total.
H.A.
The 300 Club
 
Posts: 461
Images: 0
Joined: Tue Nov 15, 2011 8:16 pm
Top

Re: Confused about inverter ground

Postby noseoil » Thu Oct 01, 2015 7:50 am

Lauren, the 110v outlets should be grounded to a point outside the trailer or its frame. If you're using shore power, the supply line will have 3 wires (black, white & copper) so the bare copper is grounded (outside) to whatever ground is provided by the house, pedestal or box you're plugged into at that time. It's fastened to the grounding lug at the outlet box, just as in a house circuit. Second the idea of a polarity tester to keep handy when you park & get out the extension cord.

I found a plug at the local Home Delay store, which is a simple 30 amp male plug with a 15 amp female (regular house type 3-pin configuration) on the back side. It will be available at an electrical supply house or larger home center near you, but you may have to ask where they're hidden in the store.

With 110v power, you need that ground to send any stray electrons to ground. That way you don't become the fuse from any leakage current which escapes the circuit & tries to run amok in the trailer.
Build log: viewtopic.php?f=50&t=60248
The time you spend planning is more important than the time you spend building.........

137905
User avatar
noseoil
1000 Club
1000 Club
 
Posts: 1820
Images: 669
Joined: Sun Apr 27, 2014 8:46 am
Location: Raton, New Mexico, living the good life!
Top

Re: Confused about inverter ground

Postby Dale M. » Thu Oct 01, 2015 9:05 am

Um, the current terminology in a DC circuit is the red wire also called positive is the OUTGOING or POWER side and the black wire and called negative or the RETURN or GROUND is technically wrong when in the DC world the ELECTRON FLOW through conductors/circuits is actually from the negative terminal of battery or power supply or generator to the positive terminal.... Or from the more negative terminal to the less negative terminal but not necessary to ACTUAL "ZERO" ground....

So when we describe how power is transmitted and used in a DC circuit we are basically wrong in the what we describe is the opposite of the actual world of the physics of how DC circuits operate...

If I have confused you then just forget about the physics involved and wire your devices in the common way we are accustomed to doing it....

Dale
Lives his life vicariously through his own self.

Any statement made by me are strictly my own opinion.
You are free to ignore anything I say if you do not agree.

Image
User avatar
Dale M.
2000 Club
2000 Club
 
Posts: 2693
Images: 18
Joined: Thu Jun 09, 2005 8:50 pm
Location: Just a tiny bit west of Yosemite National Park
Top

Re: Confused about inverter ground

Postby drshoe » Thu Oct 01, 2015 9:23 am

I have read some rigorous debate in a thread on this board about whether it's safe to ground the AC to the frame :shock: buyer beware, I guess.

Connecting the AC system and the DC system to a common ground is for personal protection should something go horribly wrong, but even when everything is working perfectly it should still be done to protect the equipment.

In my experience running an AC system near a DC floating ground system will certainly result in electromagnetic induction of an alternating current in your direct current wiring. Granted I have never seen this effect exceed 100millivolts, but it is enough to affect any screens, radios, etc. that are running on the DC. If ALL you have is lights might be no big deal, but do you want to be the one to find out if your nice new inverter can handle that? Best to listen to the people who built it.
User avatar
drshoe
Teardrop Advisor
 
Posts: 70
Joined: Mon Jul 20, 2015 4:38 pm
Top

Re: Confused about inverter ground

Postby drshoe » Thu Oct 01, 2015 9:27 am

Dale M. wrote:the physics of how DC circuits operate...


I think a lot of people have trouble even with the concept of a circuit. I explain it by saying electrons have to be pushed from one direction AND pulled from the other.

You could lick either post of your deep cycle battery if you wanted, you could even do it while you are connected to earth ground, just make sure you don't touch the other post or connect it to earth while you're doing so.
User avatar
drshoe
Teardrop Advisor
 
Posts: 70
Joined: Mon Jul 20, 2015 4:38 pm
Top

Re: Confused about inverter ground

Postby lfhoward » Sat Oct 03, 2015 9:20 pm

Here's a very interesting read.
http://www.rvnetwork.com/index.php?showtopic=106689

If I understand right, the grounding screw on the inverter is there for the AC ground, not the DC side of the system. So, if there is a fault and the AC ground wire is energized, and the screw is bonded to the trailer chassis, the trailer becomes energized with AC. If you happen to be standing in wet grass and touch the trailer frame... Zap! You become the fuse between the trailer and the earth. This is assuming the chassis has no earth ground of its own, and the trailer is using the inverter, not shore power. The point is also made that some inverters internally bond the "neutral" AC pin and the ground together, which can also create a charge differential between the trailer and the earth if the ground screw is bonded to the chassis (potential zap). I will need to use my multimeter and check for continuity to see if this is the case.

The conclusion in the 3-page thread above is to NOT connect the ground screw on the inverter to the chassis. Now in my case, there is a metal leg on the tongue that might facilitate an earth ground from the chassis, so maybe the ground connection from the screw to the chassis would work properly if the leg is deployed and the trailer is not hooked up to my TV and "floating."

My inverter works fine without connecting the ground screw - I hooked it up to the battery bank today. No part of the trailer's electrical system grounds to the trailer frame currently, so it is always safe to touch the metal floor. I am still on the fence about whether to connect the inverter's ground screw to the steel chassis. In either scenario, the GFCI should trip and save the day if anything went wrong.
My off-road camper build on an M116A3 military chassis:
http://www.tnttt.com/viewtopic.php?f=50&t=62581
Tow vehicle: 2008 Jeep Liberty with a 4 inch lift.
User avatar
lfhoward
1000 Club
1000 Club
 
Posts: 1369
Joined: Wed Jan 22, 2014 6:10 pm
Location: Philadelphia, PA
Top

Re: Confused about inverter ground

Postby Dale M. » Sun Oct 04, 2015 9:31 am

The only problem is with your comment and article is if the inverter fails and can makes frame hot, there is no circuit to ground to complete loop that possible cause a shock hazard because the voltages involved are floating and have no reference to earth ground and even if you touch earth (ground) and energized frame there is no shock hazard becasue there is no complete circuit becasue there is no EARTH reference (current path) to ground...

IF you have a jack and it is solid metal (no plastic or rubber wheel or wood blocks) planted into damp earth then you have a safety ground (of sorts) same as if you are plugged into correctly wire shore power and since this circuit is references to EARTH you still do not have shock hazard unless you actually contact the 120VAC out put of inverter and it is references to ground (not a floating ground) ... If inverter fail and makes chassis hot through its safety ground you are probably protected becasue the inverter its self or associated circuit should sense failure and shut down or disconnect inverter and you should also be protected by the fact the chassis is grounded to earth and if not its totally isolated becasue if floating with no earth reference ....

Ground inverter IF instructions say to....

Dale
Lives his life vicariously through his own self.

Any statement made by me are strictly my own opinion.
You are free to ignore anything I say if you do not agree.

Image
User avatar
Dale M.
2000 Club
2000 Club
 
Posts: 2693
Images: 18
Joined: Thu Jun 09, 2005 8:50 pm
Location: Just a tiny bit west of Yosemite National Park
Top

Re: Confused about inverter ground

Postby lfhoward » Sun Oct 04, 2015 5:12 pm

On the subject of the inverter ground:
I tested for continuity and here is what I found.

1) The inverter ground screw is continuous with the ground on the inverter's 3-prong GFCI AC outlet.

2) It is also continuous with the metal inverter case (no surprise there).

3) What was a surprise is that it is continuous with the metal case of the nearby battery charger. It is also continuous with the ground pin on the power inlet on the side of the trailer.
So, what is going on here? The inverter is plugged into one side of the automatic transfer switch, and the battery charger is plugged in on the other side of it, where the shore power comes in from outside. The automatic transfer switch has a common internal grounding block, so regardless of which side the power is coming from, the ground wire is the same.

4) Another interesting connection is that the ground screw on the inverter is continuous with the "neutral" (wide) side of its own power outlet. That means the neutral and the ground wires are tied together inside the inverter.

5) Currently none of the components I've listed above have any continuity with the steel trailer. The electrical system (both AC & DC) is floating.

If I do ground the AC inverter to the trailer chassis as the instructions say to do, I should probably ground an outlet on the other side of the transfer switch also. I am not yet convinced I should have a cable from the battery's negative post to the trailer frame, as the AC and DC systems are separate. If there is an AC fault and the trailer is energized, the electrons could flow out the tongue, down the metal front support leg, and into the earth. In this case, I would never be running the inverter with the trailer attached to the Jeep and the metal leg not deployed and in contact with the earth.
My off-road camper build on an M116A3 military chassis:
http://www.tnttt.com/viewtopic.php?f=50&t=62581
Tow vehicle: 2008 Jeep Liberty with a 4 inch lift.
User avatar
lfhoward
1000 Club
1000 Club
 
Posts: 1369
Joined: Wed Jan 22, 2014 6:10 pm
Location: Philadelphia, PA
Top

Re: Confused about inverter ground

Postby Dale M. » Mon Oct 05, 2015 9:59 am

Its simple manufacturer has the safety ground (AC socket "inverted "U") and case ground and GFCI ground and negative battery input cable all tied "common" inside inverter... As it should be IF your measurements are correct and you are not measuring continuity through internal components .... So this whole discussion has been moot as manufacturer did the right thing by design and manufacturing all the ground safety into unit to start with....

Would suggest conversation with units manufacturers tech support to see if your findings are valid....

Dale
Lives his life vicariously through his own self.

Any statement made by me are strictly my own opinion.
You are free to ignore anything I say if you do not agree.

Image
User avatar
Dale M.
2000 Club
2000 Club
 
Posts: 2693
Images: 18
Joined: Thu Jun 09, 2005 8:50 pm
Location: Just a tiny bit west of Yosemite National Park
Top

Previous

Return to Electrical Secrets

Who is online

Users browsing this forum: No registered users and 7 guests