12V wiring negative returns and fuse block bus bars

[gearsoup]

While I've accumulated most of the bits and bobs needed to wire the camper, I'm only now starting to seriously think about doing the actual wiring and system implementation. I'm certain this is going the first of many questions, but we all have to start somewhere, right?

First question: For all (or most) of the 12v circuits, should I run a separate ground wire back to the Blue Sea Systems fuse block for each circuit, or is it standard practice to "daisy chain" all grounds into one common ground that does go to the block? Looking at the images in Tony's book, it appears he adopted the latter approach (although I don't see it explicitly stated in text).

Current circuit needs:

Camper specific:
200w solar panel
314aH lithium battery
Exterior porch lights (LED, amber, 3-way switch)
2X interior LED "puck" lights on a 3-way (one with dimmer controls)
2X LED galley lights
2X 12v outlet (CPAP, electric blanket)
1x 12v dedicated circuit for fridge
2-3X USB-C for device charging
MaxxAir vent
Shore power going to 120v 3-slot breaker, dispersed to 2x GFCI outlets (one in front, one in rear)

Trailer:
Brake/Tail Lights
3rd brake light
Backup lights
Corner marker running lights

 

[featherliteCT1]

IMHO, the best practice would be to run all of the appropriately sized negative wires from each load back to a single bus bar. Then run a single, appropriately sized wire, from the negative bus bar to the Blue Seas fuse block (sized to handle the total continuous load of the entire fuse panel).

I would run the positive and negative wires side-by-side (using high strand, tinned copper, duplex marine wire).

Making correctly crimped terminations is very important.

 

[gearsoup]

Ok, the bus bar might be the bit that I missed in Tony's book. I'll reread that section
And roger that on the wiring, I've got a 100ft spool of 14-ga (which, from what I'm reading, might be a bit overkill) that I bought from McMaster-Carr. It's strand wire, but not tinned. I'll search for tinned and duplex marine

 

[Tony Latham]

Looking at the images in Tony's book, it appears he adopted the latter approach (although I don't see it explicitly stated in text).

My apologies for not adding it to the text.

I find it easy to run a dedicated negative wire to each appliance, and I use that word to include any outlet. As you can see in this photo, I use red & black two-wire cable to keep things organized.

The stuff that looks like Romex is 12-AWG two-wire marine cable that will be connected to the battery.

And as you can see, I recommend a fuse box with a negative bus bar.

Tony

 

[reaver]

I would recommend not daisy chaining your negative wire. If your negative wire fails, it could kill, all the circuits in the trailer, and since all the wiring will be hidden, it becomes very difficult to diagnose.

In ran individual positive and negative wires for pretty much everything in my trailer, and built harnesses for all my switches, diesel heater controls, etc. I used a slightly different setup than Tony, in that I didn't use a blue sea fuse block, but instead went with a fuse panel with negative bus. Same, idea though, with a slightly different execution.

Here's my diagram, if it helps:

And some images of my final wiring setup:

 

[MickinOz]

Being a fan of keeping it as simple as possible, I chose a fuse block that had negative connections. All 12V loads are connected via 2 core cables. Then an appropriately sized black and red wires to the load connection on the charge controller. Here is a picture of it installed, plus a picture of the unit I borrowed from the Ebay advert. Mine is 6 circuits, a 12 circuit one is also available.
They come with a clip-on cover, etc. I reckon I've been using my trailer for 5 years now, this has not given any trouble.

 

[gearsoup]

Related question; There will be two LED reading lights/usb charging stations in the cabin. Each one on their own circuit, or is it ok to tie into one to power the other? I suppose same goes for the cabin and galley lights; each zone would be its own circuit, but the lights for each would be sourced from one spot on the fuse block (both will have dimmer switches to keep the lights low)

 

[Tony Latham]

but the lights for each would be sourced from one spot on the fuse block (both will have dimmer switches to keep the lights low)

That's fine. Two runs from one fuse.

Tony

 

[Pmullen503]

That's fine. Two runs from one fuse.

Tony

Agreed, just remember the fuse is there to protect the WIRING. Don't over fuse (use heavier wire). The fuse should be sized for the smallest single WIRE in a circuit, not the total load.

If the total load will exceed the capacity of the smallest wire, split the circuits over several fuses.