On any given circuit the ground wire should be the same size as the supply wire. A circuit is defined as from one positive terminal through the load to the negative terminal.

On points where a piece of equipment is providing a chassis ground for its metal case, use the size the manufacturer suggests. This is a ground used to prevent the case being at a floating ground that is different potential from another ground. Like when a House battery system is not grounded to the Vehicle ground the House ground would be floating in reference to the body panels on the vehicle.

If the house and vehicle grounds are tied together it reduces the possibility of a differential creating any problems between two independent electrical systems by making their ground references the same.

This gets more complicated when AC is brought into the picture, particularly with connecting to Shore power. If the Shore power source is incorrectly wired (Hot and Neutral swapped) it can create a very dangerous situation where the chassis of the van (if tied to AC neutral/ground) becomes Hot in respect to Earth. Always use a tester on any Shore power outlet before connecting to the vehicle.

 

What do you mean by ground wire? Are speaking of the 12v negative or a true ground wire to the vehicle's chassis ground? Do you have a schematic?

 

I'm referring to grounding to the vehicle's chassis.
Here is my schematic:

 

@Travlin I think I was misunderstanding the concept of "ground". Providing a chassis ground for the inverter is one thing. The other is that what I'm showing in my diagram as a chassis ground from the negative bus bar should really be a connection to the negative battery terminal of the vehicle's battery. This would be the complete circuit originating from the CCP (Customer Connection Point) via the Sterling B2B.

 

This would explain the absence of the battery itself in the diagram.

Yep, all electrons want to flow from the negative to the positive terminal through the load(s) that do the fun stuff for us. So, yeah, you just need to add that cable at the appropriate gauge from the buss bar back to the battery.

The choke point would then be the 60 Amp CCP side of things where your power is coming from. You may want to consider adding a House battery which will isolate your RV loads from the vehicle battery and keep you from inadvertently stranding yourself by leaving something turned on.

With all the thought you have put into this, a little redundancy might be a good bet to place.

 

I think 8' of AWG4 for connecting negative buss to ground is fine. That would be .002 ohms. The highest current of 40A (charging from alternator, limited by your 40A fuse) would produce less than .1 V drop. During bulk charge cycle that small voltage drop is not too critical. If it were me I would use a shorter ground wire to the nearest chassis ground instead of running long wire to the "Factory approved ground point". Make sure to scrape off the paint on the chassis and use star washer.

The more critical path you may want to consider upping cable thickness is the connections to the 1000W inverter. You already have fairly short cables there so you maybe fine.

Make sure to use good terminal connectors and good crimping practice.

 

If you are referring to the ground wire to the BEMM point 25 terminal near the E-brake then the cable should be sized for the ampacity of the Sterling DC-to-DC charger you are using and the total (+ and -) length of that run. You have it connected to the CCP with 4 and then continue with 6 gauge after the breaker. Not sure why you are using the 4 gauge when the rest of the run is 6. The whole run should be the same size.

I would use Sterling's recommendation of going directly to the chassis battery. Their units sense battery voltages so that would provide the most accurate value. (least voltage drop)

If you plan to upgrade the DC-to-DC charger to take better advantage of the the full 60A capacity of the CCP then you may want to consider that in your cable sizing. We always bump up a gauge to minimize voltage drop. If the cable is small and gets warm from use then resistance increases and so to the voltage drop. It can become a vicious circle that we want to avoid. Honestly, I don't understand why you would not want to take more advantage of the available 60A. That will make your batteries charger faster with less driving. This is why we use the the Kisae DMT-1250 which delivers 50A. It is well matched to the 60A available.

All the best,
Hein
DIYvan
541 490 5098

 

I own a Sterling BBW1260, Sterling provided an already installed Negative Ground wire with a inline fuse holder, The Negative Ground wire is 10 gauge with a 20 amp fuse installed from the factory. (The ground is Fused)

I realize you have a different model Sterling, But my Sterling is a 60 amp model and it only requires a 10 gauge ground wire, I would say you should be fine with a 6 gauge Negative Ground wire on yours.

Here is a link that provides more info on how to install the same model Sterling as you have:


https://marinehowto.com/understanding-the-sterling-power-pro-batt-ultra-battery-to-battery-charger/