Grounding!

[GuitarPhotog]

OK, I have on my asbestos flame suit, and have activated the flame fighting system, so I can talk about electrical grounding in an all-metal teardrop trailer.

When I first started renovation of my 1948 all-aluminum classic teardrop, I read all the grounding threads and decided that, for me, the answer of whether to connect my 120 VAC shore power feed to chassis ground was the National Electrical Code, that states that the trailer must be connected to the green AC ground.

That was fine for the last year, and has caused no issues or uncertainty, until now.

I recently converted my trailer's "road" wiring from a flat-four connector to a modern 7-way. So I can charge my trailer battery from the TV. The trailer was built in 1948, so none of the original light fixtures (tail/brake/turn signal) have a ground return wire. They all rely on the chassis for the return. So I wired my new 7-wire harness the same way, running a ground return all the way out to the tail light and connecting to the chassis there.

And to be able to charge my trailer battery from the TV battery, I had to hook the trailer 12V return to the TV 12V return.

Now I've got both my 12VDC accessory power (lights, fans, phone charger) and my 120VAC connected to the trailer chassis. And when the trailer is hitched to the TV, there's a fairly low-resistance, but intermittent, ground path through the hitch ball

I'd like to hear some rational opinions (if there are such given this subject) about the advisability of common grounds. It is likely that at some point the trailer will be connected to shore power and the TV at the same time. I do not plan to install a cut-off switch between the TV and the trailer because I can just disconnect the cable.

Thanks,

<Chas>

[eamarquardt]

Your a/c and d/c systems work independently. The only place for a/c current to return to (from the hot lead) is ground or neutral. The only place for electrons that leave the battery to return to is the positive terminal (they actually leave the battery from the negative terminal). So, having a common ground for both the a/c system and the d/c system isn't a problem.

Re: "individual ground wires". If you aren't completely bald or shave your head, you'll eventually pull a bit of your hair out sorting out grounding issues if you rely on a chassis ground system w/o routine maintenance to ensure all of the connections to the frame are free of corrosion. Individual ground leads make the whole system more reliable.

Hope this helps.

Cheers,

Gus

[Dale M.]

I don't see any problem with one "leg" of the circuit (referred to as "ground") tied common... As long as there is only one conductor in "circuit" the is common and voltage differentials and power types (AC/DC) do not try to loop through other circuits ( or people) to make a complete electrical path...

In the telecommunications industry we have a concept called GROUND WINDOW (other industries as well).... Does pretty much what you describe as doing on your trailer..... May also be referred to as "Single Point Grounding"....

IF you really want confusion try reading a few "papers" found in link below...

https://www.google.com/search?source=ig ... 3j6j4.13.0.

https://www.google.com/search?hl=en&saf ... UGP0g1G_ZA

Dale

[Corwin C]

This is a common question and there is a veritable plethora of advise out there, both good and bad.

Quoting myself from this thread...

I think that a lot of the confusion with ground in an AC circuit is the term "ground" itself and how it is used differently in AC and DC wiring.

In DC, the return path to complete the circuit is often referred to as "ground." In many cases, metallic components of the trailer are used as a path to complete those circuits instead of an actual wire.

In AC, the hot and neutral wires complete the circuit. ONLY wires, buss bars, switches/breakers, and appliances are used to complete that circuit. The ground is ONLY energized when/if something goes wrong. In normal everyday use, it NEVER carries any current. However, if something does go wrong, and since electricity ALWAYS follows the easiest path, the ground is designed to be the path that completes the circuit path instead of a person/pet/etc. Furthermore, grounding can only help if it is connected. If you want to eliminate the possibility of a surface/object being energized, it MUST be electrically bonded to "ground" in a proper and secure manner. My chassis/sheet metal/metallic plumbing/etc. will absolutely be grounded.

The second step here is to make sure that the power source that you plug into is properly wired. There are inexpensive indicators which simply plug in and will let you immediately determine if your power source is wired correctly. This is a critical step and should not be overlooked.

... and to clarify your question, in every application that I can think of, even though the a/c is grounded to the same potential conductor as the d/c, only the d/c is using it unless there is a problem. There is no difference in how 7-way, 6-way, 5-way, 4-way, etc. trailer plugs operate (just the number of available connections for options like charging batteries, backup lights, brakes, etc.) If the 4-flat plug worked, the 7-way will also. The ground wire from the 7-way plug should be connected to both the battery and the chassis, just like it was (should have been) with the 4-flat (especially in your application where the lighting grounds to the chassis.) Relying upon the hitch/ball connection for the ground is very unreliable and will cause issues sooner or later.

[Martiangod]

hitch grounding always rears its ugly head at the worst time.....

" I wonder why all the clearance lights are blinking when I turn "

" Honest officer, the lights were working when I left home"

" What do you mean the fine is going to be $$$$ "

[GuitarPhotog]

Just to clarify, the main ground return path is not through the hitch, it's through the 7-way connector. I mentioned it only because a parallel, intermittent ground return path through the hitch exists.

I come from the audio world where parallel ground return paths are often problematic.



<Chas>

[eamarquardt]

I come from the audio world where parallel ground return paths are often problematic.


<Chas>

You are now, though, in "The Teardrop World" and the "Laws of the Audio World" do not apply. Congress passed a law "making it so". They, rumor has it, did the same thing with the "Laws of Thermodynamics".

Trailer lights, in most instances are pretty simple. On or Off. No amplifiers, inductors, capaictors, feedback, etc. Even so Murphy seems to make his presence known.

Cheers

Gus

[GuitarPhotog]

If congress thought they could repeal the laws of thermodynamics, they'd try.

The world of teardrops is much easier and more laid back than the world of audio.

I finished the last of the wiring today. Everything checks out, with and without the TV, so we should be good to go to the DAM Gathering in a couple of weeks.

<Chas>

[Corwin C]

I generally plug the trailer lights in and check them before setting the hitch on the ball. That way I know that my ground through the plug is working and not being affected by that nasty parallel ground through the hitch. It also helps when troubleshooting.