12V wiring Aluminum Cargo Trailer conversion

[SlideInDad]

Been searching for days and haven't found a clear answer on whether or not a 12V system should be grounded to the chassis of a 100% aluminum framed enclosed trailer. Am I better running negative wires back from every light and fan back to the batteries or will the aluminum frame conduct well enough without corrosion?

All my searches regarding grounding aluminum framed trailers talk about vehicle wiring from the truck back for running lights/directionals... This line actually says do not ground to the trailer chassis: Aluminum trailer grounding But my question is for a house 12v system unrelated to the tow vehicle.

[CA_Traveler]

Bonding is a basic saftey practice. A very small AC leak to a ungrounded RV can cause a significant shock. Typically these leaks do not trip a CB and can exist even if the CB is tripped - I could be before the CB or it can occur from the negative AC lead.

A little extra wire and connections diverts this current/voltage back to the shore panel via the AC ground wire. This is a basic safety requirement and replaced 2 wire plugs many years ago with 3 wire plugs.

[DrewE]

SlideInDad wrote:

If the IOTA45 converter is simply properly bonded to my house 120V what purpose would the chassis ground serve?

The converter chassis needs to be bonded to the RV chassis (as is detailed in its installation manual), and the 120V ground needs to be bonded to the RV chassis.

The 120V ground to chassis connection is for safety in case there should be an electrical fault in the 120V wiring, causing the hot to short to the chassis. If the chassis were not grounded, it would be hot and pose a shock hazard to anyone entering or exiting the RV (a hot skin). Having it bonded to ground prevents that, and assuming the short is low enough impedance causes the breaker to trip due to overcurrent.

The 12V bond is a bit more subtle. As I understand it, it is practically speaking impossible to totally isolate the chassis from 12V negative ground with typical appliances and lights, and so it's likely that the chassis will be connected to the 12V negative side somehow or another. If there's not a good bond between the battery and the chassis, and the converter output and the chassis, then there's the opportunity for all of the converter current to find its way through e.g. the 120V ground wire or the ground wires for various 12V appliances back to the battery in the case where the main wire from the converter's negative output to the battery is broken or disconnected. This amount of current can easily be a dangerous overload for those wires; hence, as a safety precaution, they must be tied to the chassis with a low impedance wire that will carry the fault current safely.

Assuming you have electric trailer breaks with a breakaway switch, the trailer chassis will have to be grounded for that system to work properly. (I guess that's also assuming you're using the house battery for the emergency braking power, which is standard practice. Having to maintain two separate batteries when one will do just fine on its own seems...well, silly.)

[SlideInDad]

So I found this article which is quite descriptive of chassis grounding. RV electricity part 1 and
Part 2

It would seem that the ground-plane used for most RVs DC system is for the purpose of serving as a negative return for DC appliances.

The true focus of the ground discussed in these articles is:

"properly “grounded” your RV chassis must have its EGC wire properly “bonded” (connected) to the power company’s service panel “ground/neutral/earth” bonding point. And that bonding must provide an under-1-ohm connection for the neutral of the transformer on the power pole to return any fault currents back to whence they started (in the transformer)"

Since it's become very clear in all my research to date that I should not return any negative DC current via the 100% aluminum chassis of my trailer (will run negative wires from every appliance back to the fuse panel instead) it's starting to sound like the real concern I should have is simply my shore power connection as I will be running zero AC appliances in this trailer beyond the 120 to the converter while at home for charging or connected to my generator while boondocking. I think in the past 20 years I've been to a campground with shore power connections only twice.

Am I on the right track here? Ultimately I'm looking to setup a pure 12V power system on my trailer hopefully 90% of the time charged from my 200W solar setup. My draw should be minimal compared to my old TCs as I will have no inverter and no heavy draw appliances. Really just lights and fans (fantastic fan, propane furnace fan, window DC fan, USB charging station for phones/laptop).

If the IOTA45 converter is simply properly bonded to my house 120V what purpose would the chassis ground serve?

[MEXICOWANDERER]

The NEGATIVE is not a corrosion issue

It is a GALVANIC ISSUE.

Never use any part of a non noble metal as part of an electrical circuit. The circuit must be totally isolated from both AC and DC electricity.

Load negatives back to a distribution block. Distribution blocks to a central bus bar which will connect to the trailer battery AND the wire to the tow vehicle plug. Being mechanically connected to the two vehicle influences nothing. But connect bo grounds to trailer chassis or frame.

[Fisherman]

SlideInDad wrote:
Should I bolt a grounding block onto the aluminum frame? I saw comments of no copper against aluminum but what about a steel grounding block on the chassis?

Any dissimilar metal will have galvanic reaction, even steel on aluminum. How about mounting the grounding buss bar somewhere on a spot on wood.

[SlideInDad]

Should I bolt a grounding block onto the aluminum frame? I saw comments of no copper against aluminum but what about a steel grounding block on the chassis?

[Horsedoc]

Wire it like a house and don't take any chances

[DrewE]

WNYBob wrote:
I think you have missed the point that there are 2 separate 12v systems in a TT. One is the TV (tow vehicle and the DMV lighting) circuit and the other is the TT. They should not be mixed.

Both ought to be bonded to the trailer frame, though, regardless of whether that forms the negative return for current or not. For the house electric system, if there is a converter included, I think this is a requirement of the NEC. (Similarly, the 120V ground needs to be bonded to the chassis.)

[Dusty_R]

There is an anti-oxidizing paste/grease used on aluminum wire. If you do use the aluminum body for the 12v ground be sure to use past/grease on all places where grounding to the body. And do not fasten copper wire to the aluminum body.

Dusty

[CA_Traveler]

Poor grounding is a common problem. Keep it corrosion free and use anti corrosion product.

[WNYBob]

I think you have missed the point that there are 2 separate 12v systems in a TT. One is the TV (tow vehicle and the DMV lighting) circuit and the other is the TT. They should not be mixed.

[opnspaces]

I think most RV's have interior ground wires coming back to the electric panel. You could try reaching out to Jayco or any other manufacturer customer service and ask them how the interior lights are grounded.

[SlideInDad]

CA Traveler wrote:
Your link sounds like a concern for corrosion which can become a problem. Good maintained grounding would do the job. 10 ga is likely over kill for the running lights ground especially for LED lights.

Are you going to use the TV to charge the trailer battery? Regardless I'd ground the 12V interior system including any incoming AC to the trailer.

Aluminum conductivity would not be a concern for me but long term corrosion can be a issue.

Trailer house batteries will be charged by solar and a IOTA 45 converter when connected to AC via either a generator or when at home. Exactly what do you mean regarding a well maintained grouding? Cleaning were it grounds to the frame from the batteries frequently?

[CA_Traveler]

Your link sounds like a concern for corrosion which can become a problem. Good maintained grounding would do the job. 10 ga is likely over kill for the running lights ground especially for LED lights.

Are you going to use the TV to charge the trailer battery? Regardless I'd ground the 12V interior system including any incoming AC to the trailer.

Aluminum conductivity would not be a concern for me but long term corrosion can be a issue.