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.

[3_tons]

djglover7 wrote:
I was responding to *your* post.

Thanks for the clarity, sorry for my poor re-read (dummy me - lol), I was only running on 7 dang cylinders...

[djglover7]

I was responding to *your* post.

[3_tons]

djglover7 wrote:
Thank you 3tons.

"I would note that AFAIK, within the main, household copper wire is commonly attached to aluminum lugs harboring steel screws...".

That appears to be true for the neutral bus bar.
The ground buss bar is steel/steel.

Are we talking metallurgical compatibility, conductivity, or maybe something else - I’m somehow missing your point?... I’m of the ‘KISS’ persuasion - I’ve often seen aluminum wire and copper wire and steel components co-mingled within the same Main...BTW, your aluminum chassis is a far better conductor than steel, yet steel is commonly employed as an effective ground return in all vehicles...You’ll be fine so long asyou apply a small dose of De-Ox...

[djglover7]

[djglover7]

Thank you 3tons.

"I would note that AFAIK, within the main, household copper wire is commonly attached to aluminum lugs harboring steel screws...".

That appears to be true for the neutral bus bar.
The ground buss bar is steel/steel.

[3_tons]

I would note that AFAIK, within the main, household copper wire is commonly attached to aluminum lugs harboring steel screws...

[3_tons]

djglover7 wrote:
All,
My one unresolved issue is:

*IF* I bond/connect 12VDC negative to chassis *AND 120VAC ground to chassis, is there *ANY* issue with voltage surges/spikes/daemons going from AC to DC?

The big concern is surges/spikes/daemons going from AC to the tow vehicle (DC).

Please advise.

Answer: No, this is common accepted practice...

[djglover7]

[djglover7]

All,

I have added a ground link (10AWG) from the AC ground bus to the chassis.

But, before I made the connection, I wanted to test whether or not the 12VDC positive would close the circuit to chassis ground. My assumption was NO as I have not seen any AC grounds to the chassis.

(Note: this is a DIY toy hauler that I purchased and I inherited all the undocumented work.)

When I did the test with a simple 12VDC circuit tester, I showed a complete circuit (i.e. light came on). So, somewhere, one of the receptacles is grounded or one of the appliances is grounded to chassis. (I also assume that if a bare grounding were to touch the chassis, no issue).

I think I am safe now and I can continue with locating the mystery grounding points.

[BFL13]

Yes, the 120v and 12v share the same RV frame for ground (120)/neg (12). Typical RV power centre has the 120v incoming to the 30a Main breaker with the bare ground wire going to the RV frame. Meanwhile the converter in that power centre uses the same RV frame for much of its several neg paths to the various 12v items such as slide motor, jacks, etc. The metal skin of RVs that have that is the negative path for the clearance lights too.

The metal casing of the power centre is grounded to the frame as is the "lower portion" 's metal casing (chassis) so that is the "chassis ground" for the converter. If you have a deck mount converter it will have its own chassis ground from a lug on its metal casing. Same with a bigger inverter.

Warning--do not bring the chassis ground of an inverter back around to its own neg input terminal. That does get to the frame via the battery's neg ground to frame, but you are supposed to run the inverter chassis ground direct to the frame.

Those inverter chassis grounds are to reduce radio interference.

[wa8yxm]

IF you want 'Best results' there is a special connector to connect copper to aluminum. beyond that I have no knowledge as I've never actually seen one

I'm guessing a ring terminal with an aluminum screw to the chassis (or bolt) is the order of the day but the ring terminal is crimped onto the copper and it is a SPECIAL type of terminal made for that job.

[djglover7]

All,

I am slightly comforted seeing others have questions on grounding. This thread has been very informative.

I am utilizing 3 voltage systems, 12VDC chassis, 12VDC coach, 120VAC shore. There is a coach battery that supports various chassis and coach power.

My one unresolved issue is:

*IF* I bond/connect 12VDC negative to chassis *AND 120VAC ground to chassis, is there *ANY* issue with voltage surges/spikes/daemons going from AC to DC?

The big concern is surges/spikes/daemons going from AC to the tow vehicle (DC).

Please advise.

[DrewE]

SlideInDad wrote:

DrewE wrote:

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.)

I do have a breakaway system with an old dead battery, was figuring on wiring it to the new 12V house battery system. I haven't looked yet but assumed it was grounded back to the Tow Vehicle?

The ground for the trailer brakes (and hence also the ground for the brake lights and whatnot) needs to be connected to the negative of the battery, and the positive from the battery goes to the breakaway switch, and the other side of the breakaway switch to the brake coils in parallel with the brake wire from the tow vehicle connection. The ground connection can't go back all the way through the tow vehicle, of course, since the whole point is to activate the trailer brakes should the trailer and tow vehicle become separated from each other. It is shared with whatever ground is there from the tow vehicle connection, which I think might be what you meant.

I did a tiny bit of research, and apparently the accepted best practice for aluminum trailers is to run ground wires to the brakes and lights and still bond the frame to the ground connection from the tow vehicle. The bonding among other things helps prevent static buildup (I assume mainly from the tires rolling down the road). Apparently sometimes the brakes and lights are both grounded to the frame themselves and also grounded via a ground wire; for many trailer lights, they'd be grounded to the frame simply by being installed unless special care was taken to electrically isolate them. I had been under the impression that brakes were at times similarly grounded via their mounting to the axle, but it seems that was a false impression--they have wires for both sides of the coil to be connected up.

[SlideInDad]

DrewE wrote:

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.)

I do have a breakaway system with an old dead battery, was figuring on wiring it to the new 12V house battery system. I haven't looked yet but assumed it was grounded back to the Tow Vehicle?