WFCO DC ground bus?

[epearce]

So, I'm installing my We Boost, thought it would be straight forward to tap a new 12 VDC branch off the WFCO. There are two open branch circuits, but where is the DC ground bus bar? Do I have to pull the whole box out?

[Yoda]

So, I'm installing my We Boost, thought it would be straight forward to tap a new 12 VDC branch off the WFCO. There are two open branch circuits, but where is the DC ground bus bar? Do I have to pull the whole box out?

Have you pulled the outer cover to see the wiring connections. Look for where green or plain copper wires connect - that is the chassis ground buss bar. There will also be a bar where all the white wires connect. That is the neutral bar. Do not connect to that one.

The bar on the left side is ground

Hope this helps
Keith

[Country Campers]

I am not sure that the DC ground is connected to the AC ground, I would want to keep these 2 separate for some reason that maybe the electrical gurus will tell us why or why not.

The right side of the pictured posted above is the DC side of the power distribution panel, the top 2 white and one black should be the DC ground, I am not sure if there is a DC ground bus, I think most of the DC grounds are bundled together and ran to the chassis or the battery.

Brian

[epearce]

Thanks. Yes, that is exactly what mine looks like--except for some of the DC fuses. I guess I was expecting a separate 12VDC and AC inverter ground. They share the same bus bar?

[StephenO]

Thanks. Yes, that is exactly what mine looks like--except for some of the DC fuses. I guess I was expecting a separate 12VDC and AC inverter ground. They share the same bus bar?

Hey Eric
I've seen in another forum, pictures from the same series and year of trailer as mine, showing behind the WFCO power distribution panel and there was the DC negative bus bar. I would check there.

I believe the AC ground bus bar will be connected to the chassis, same as the DC negative return, but I wouldn't connect the DC grounds to it.

[acoleman43]

epearce my DC ground bus was attached to the floor behind the DC panel. I had to pull the panel out to access it...even with the panel removed I had to dislocate my elbow and wrist to reach it.

[Yoda]

I am not sure that the DC ground is connected to the AC ground, I would want to keep these 2 separate for some reason that maybe the electrical gurus will tell us why or why not.

The right side of the pictured posted above is the DC side of the power distribution panel, the top 2 white and one black should be the DC ground, I am not sure if there is a DC ground bus, I think most of the DC grounds are bundled together and ran to the chassis or the battery.

Brian

Brian on my trailer the AC ground bar is grounded to the trailer frame.

Copper Wire to frame comes from AC ground bus bar. I believe the white wire comes from the 12V negative connection (top left 12v side in picture above) too.

The chassis ground on the 12V side does the same in the front compartment, so I don't see a difference. Then again I let the smoke out of the wires sometimes.

On edit I do remember a 12v negative bus bar behind the power panel too.

[howson]

epearce , Yoda , and Country Campers -- this conversation is why it frustrates me that in a DC circuit the term "ground" is used. For a component to work in a DC circuit what's needed is a path to get from one side of the battery to the other. Think of a flashlight with a battery in it--there's no "ground", just a positive and a negative "path" from the battery to the powered component.

The simple circuit below represents this concept (using conventional flow notation). If the term "conventional flow notation" is unfamiliar, check out https://www.allaboutcircuits.com/tex...electron-flow/



So...to keep this short...what is sometimes called "ground" in a DC circuit is the negative side of the path (from component to the battery). IMO the negative side of the path is not "ground" like the ground in an AC circuit--an AC circuit's ground is there for safety. (Ever wonder why some AC appliances work fine with only a two wire plug? But let's not go down that rabbit hole.)

At this point I hope this has conveyed that "ground" when talking DC is the return path to the battery and "ground" when talking AC is the safety wire (which is hopefully never needed).

So...can the trailer frame be used for both the DC return path and AC ground? Yes.

Think of the trailer's steel frame as a huge gauge wire. For the DC side, the battery's negative is connected to the frame and then the negative side of DC powered components throughout the trailer can also be connected to the frame. Thus there is a completed circuit ("path") back to the battery like in the simple drawing above.

On the AC side, the steel frame is again used as a big 'ol piece of wire, except the path is from the trailer frame to the campground pedestal (or applicable AC power source). The path is there so if the hot side of an AC component comes in contact with a conductive part of the trailer, the hot AC goes right to the trailer frame, back to the pedestal, and back to where it came from (power company, etc). If that happens current will flow for a super short time 'cause a circuit breaker is going to open somewhere in the circuit.

There's additional "gotchas" with this topic that the engineers here could expand on--my purpose was to convey the concepts in simple layman terms (as I understand them). J. Michael Sokol's book RV Electricity explains all this in much more detail, too.
Now regarding epearce 's original question about where the DC return path connection is in his WFCO...I'm not sure. Time for another cup of coffee...

[epearce]

howson Indeed, I agree with all those points. I did find the 12VDC- bar back behind the WFCO, sort of attached to the floor. I did not track down exactly where it goes, I assume one of the wires is the white (or black) wire on the NEG black, and the black (or white) goes back to the chassis, either at the lug on the tongue or something under the floor near the WFCO. Not quite the wiring practices I would hope for, but I guess it is tight in there for a NEG bus along the right side by the fuse block, especially when some of those 12 V branch circuits may find some local tie to the chassis.

Thanks for the reference on Sokol's book. I'll have to look that up. It does feel not best practice to share the AC ground, and the DC return, at least they are separated by some piece of probably slightly undersized white (or black) wire off that NEG block there.

Anyway, the We Boost is now neatly wired into one of the open fuses, the We Boost 12- found its way to the sort-of-secured bus bar, and its is nestled in the adjoining cabinet with a switch and everything. Now to fish the interior antenna somewhere other than inside the cabinet.

[StephenO]

epearce

Hey Eric, looks like you have a few extra spots on that bus bar on the left-hand side, does that mean that the negatives connected on the right-hand side all have their own spot? Or did they double up a bunch of the negative cables under each screw? If they did double up, maybe consider moving some of the connections to get each one under their own screw. Just a thought.

[epearce]

StephenO No, that bar on the left is the AC ground lines for the AC branch circuits. It must also go back to the frame. Yes, the DC negs sort of have their own spot, that little bar just stuffed back behind the WFCO. You can see it in the second picture. I was expecting a nice matching NEG bar on that far right side, but you get what you get. I guess that does beat the residential wirenut and electrical tape that tied the DC grounds together up on the tongue. While it would work to run that DC ground back to there, its good practice to keep the AC and the DC voltages physically separated so that if something comes loose, 120 VAC doesn't contact any of the low voltage circuits. Notice there is a plastic partition between the AC breakers and the DC fuse block.

[StephenO]

epearce , sorry Eric, I should have been clearer in my post, but I was referring to the bus bar in your second picture. That being said, it's good to hear that each DC negative was on it's own terminal.

I hear you on the large wirenut near the tongue though, another item that I may revamp this spring. I have a lot of vacation days to use this year, so I have oodles of time on my hands